Continuing the comments started in Grazing is for cattle, here's an interesting study from the Oxford Center for Diabetes, Endocrinology and Metabolism.

Volunteers were fed a test meal breakfast of Rice Krispies, a banana, and a chocolate milkshake (76.4 grams carbohydrates, 51.9 grams fat, 12.2 grams protein). Lunch was served 5 hours later and consisted of a cheese sandwich and a second chocolate milkshake 43.4 grams carbohydrates, 49.6 grams fat, 24.0 grams protein). Frequent blood samples were then assessed over the day. (Don't try this at home: These are obviously very dangerous foods!)

Here's the pattern of triglycerides that was observed (1st dotted vertical line = breakfast, 2nd dotted vertical line = lunch):

Note that triglycerides only begin to decline 3-4 hours after breakfast, only to peak higher after lunch.

Here's the pattern observed for chylomicrons, the "granddaddy" of lipoproteins that derives from intestinal absorption of fatty acids:

Both graphs from Heath RB et al Am J Phyiol Endocrinol Metab 2006.

With chylomicrons, note a similar pattern to triglycerides: Chylomicrons begin to decline at 3-4 hours, only to peak higher after lunch.

This is the first study to examine the effect of sequential meals on such postprandial (after-eating) patterns. But it makes the graphic point that, if insufficient time is permitted between meals, both triglycerides and chylomicrons will "stack" themselves higher and higher. (Chylomicrons are subjected to processing by the enzyme, lipoprotein lipase, to form highly atherogenic, or plaque-causing, chylomicron remnants.)

While not examined in this study, my bet is that "grazing," i.e., eating small meals or snacks frequently, is an extreme instance of triglyceride, chylomicron, and chylomicron remnant stacking. That can only lead to one thing: accelerated heart and vascular plaque.

When measuring blood levels of vitamin D (as 25-hydroxy vitamin D), what constitutes a desirable level?

There's no study that directly examines this question, no study that enrolled thousands of people and assigned a placebo group and groups receiving escalating doses of vitamin D and/or achieved higher levels of vitamin D, then observed for development of cancer, diabetes, depression, heart disease, multiple sclerosis, osteoporosis, osteoarthritis, etc. Such a study would requires many thousands of participants (particularly to observe cancer and multiple sclerosis incidence), many years of observation, and many tens of millions of dollars. Nope, only a drug company could afford such costs.

So we have to piece together various observations and extrapolate what we believe to be the ideal level of vitamin D. Epidemiologic observations in several cancers (breast, colon, prostate, and bladder) suggest that a 25-hydroxy vitamin D level of 30 ng/ml or higher is desirable (with less cancer incidence above this level). Other data suggest a level of 52 ng/ml or greater is desirable. Unfortunately, much cancer research looked at intake of vitamin D from food and supplement sources, rather than actual blood levels. We also have to factor in the great individual variation in vitamin D metabolism, with a single dose yielding variable blood levels (as much as a 10-fold difference). There's also the variation introduced by vitamin D-receptor variation (genetic polymorphisms).

A new study using vitamin D administration helps chart the desirable levels of vitamin D.

Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient - a randomised, placebo-controlled trial.

In this New Zealand study, 42 women (23 to 68 years old) were given 4000 units vitamin D, 39 women given placebo. Median 25-hydroxy vitamin D levels increased from 21 nmol/L (8.4 ng/ml) to 75 nmol/L (30 ng/ml). Both HOMA (a measure of insulin sensitivity) and fasting insulin levels improved, with greatest improvement seen at 25-hydroxy vitamin D levels of 80-119 nmol/L (32-47.6 ng/ml) or greater.

We also know that a vacation on a Caribbean beach in a bathing suit will increase vitamin D blood levels to the 80-110 ng/ml range without ill-effect (at least in young people who maintain the capacity to activate vitamin D in the skin, a phenomenon that declines as we age).

So do we really know the truly ideal level of vitamin D to achieve? I believe that, given the above observations, it is reasonable to extrapolate that the ideal vitamin D blood level likely lies somewhere above 50 ng/ml. We also know that vitamin D toxicity (i.e., hypercalcemia) is virtually unheard of until vitamin D blood levels approach 150 ng/ml, and even then is inconsistent. The health benefits of vitamin D supplementation are so tremendous, that I am not willing to wait for the prospective data to explore this question fully. For now, I aim for a blood level of vitamin D of 60-70 ng/ml (150-175 nmol/L).

Many dietitians and nutritionists advise many people today to "graze," i.e., to eat small snacks every couple of hours. They argue that it blocks the drop in insulin and blood sugar that can trigger greater appetite and claim it can facilitate weight loss.

This is an absurd notion. Humans are not meant to graze. Humans are meant to find a wild boar or other animal, kill it, gorge on the meat, organs, and fat, then revert to berries, roots, leaves, and other foraged foods until the next kill. A human living in the wild does not have a cupboard or refrigerator full of ready-to-eat snacks to graze on.

The several hours after a meal is the most dangerous for creating coronary atherosclerotic plaque, i.e., the post-prandial period. In other words, eat dinner and, for the next 6-12 hours, your intestinal tract degrades the food; food byproducts are absorbed into the blood or lymph system. The blood is literally flooded with the byproducts of your meal.

Postprandial abnormalities are emerging to be a potent, and much underappreciated, means of causing heart disease and atherosclerosis in other vascular territories (especially carotid arteries and thoracic aorta).

Not eating--i.e., the fasting state--for extended periods is good for you. Encouraging people to graze amplifies atherosclerotic risk, since it creates an abnormal prolonged postprandial state.

Rob was never that committed to following the program in the first place.

I met Rob because of a modest heart scan score and consultation for a cholesterol abnormality. Rob had been cycled through all the statin agents by his primary care physician, all of which resulted in terrible muscle aches that he found intolerable.

I started out, as usual, characterizing his cholesterol abnormality with lipoprotein testing (NMR):

LDL particle number 1489 nmol/L
LDL cholesterol (Friedewald calculation) 143 mg/dl
Small LDL 52% of total LDL
HDL 50 mg/dl
Triglycerides 82 mg/dl

(LDL particle number is the emerging gold standard for LDL quantification, superior to calculated or Friedewald LDL cholesterol for prediction of cardiovascular events.)

Rob is a busy guy. After only a couple of brief visits, life and work got in the way and Rob let his attentions drift away from heart health. Since the information I provided made little impact on his thinking, he reverted to the low-fat diet his primary care doctor had originally prescribed and that he read about in magazines and food packages. He also ran out of the basic supplements I had advised, including fish oil and vitamin D, and just never restarted them.

A couple of years passed and Rob decided that just poking around on his own might not cut it. So he came back to the office. We repeated his NMR lipoprotein analysis:

LDL particle number 2699 nmol/L
LDL cholesterol (Friedewald calculation) 229 mg/dl
Small LDL 81% of total LDL
HDL 53 mg/dl
Triglycerides 78 mg/dl

Two years of a low-fat diet had caused Rob's LDL particle number to skyrocket by 81%, nearly all due to an explosion of small LDL. Recall that small LDL is more susceptible to oxidation, more inflammation-provoking, more adhesive--the form of LDL particles most likely to cause heart disease.

Also, note that, despite the enormous increase in small LDL, HDL and triglycerides remained favorable. This counters the popular rule-of-thumb offered by some that small LDL is not present when HDL is "normal."

Low-fat diets as commonly practiced are enormously destructive. In Rob's case, a low-fat diet caused both calculated Friedewald LDL as well as LDL particle number to increase dramatically. In many other people, low-fat diets increase calculated Friedewald LDL modestly or not at all, but cause the more accurate LDL particle number to increase significantly, all due to small LDL.

I'm happy to say that, once Rob witnessed how far wrong he could go on the wrong program, he's back on Track. (Sorry, pun intended.) He has resumed his supplements and eliminated the food triggers of small LDL--wheat, cornstarch, and sugars.

In response to the Heart Scan Blog post, Fish oil makes you happy: Psychological distress and omega-3 index, Dr. David Grimes offered the following argument.

Dr. Grimes is a physician in northwest England at the Blackburn Royal Infirmary, Lancashire. He is author of the wonderfully cheeky 2006 Lancet editorial, Are statins analogues of vitamin D?, questioning whether the benefits of statin drugs simply work by way of increased vitamin D blood levels.

There is a fashionable interest in Omega-3 fatty acids, and these become equated with fish oil.

But fish oil is much more. Plankton synthesise the related squalene (shark oil) which, in turn, is converted into 7-dehydrocholesterol (7-DHC). The sun now comes into play and it converts 7-DHC into vitamin D (a physico-chemical process).

Small fish eat plankton, large fish eat small fish, and we eat large fish. So vitamin D passes through the food chain.

This has been a vital source of vitamin D for the the Inuits and also for the Scots and other dwellers of northwest Europe. (Edinburgh is on the same latitude as Hudson Bay and Alaska, further north than anywhere in China). In these locations there is not adequate sunlight energy to guarantee synthesis of adequate amounts of vitamin D, again by the action of sunlight on 7-DHC in the skin.

When the Scots moved from coastal fishing villages to industrial cities such as Glasgow, they became seriously deficient in vitamin D, and so the emergence of rickets. This was followed by a variety of other diseases resulting from vitamin D deficiency: tuberculosis, dental decay, coronary heart disease, and even multiple sclerosis and depression (the Glasgow syndrome).

And so it was with the Inuits. When their diet changed from fish for breakfast, fish for lunch, fish for dinner, they became deficient of vitamin D and they developed diseases characteristic of industrial cities, where there is indoor work for long hours, indoor activities, and atmospheric pollution.

It is the vitamin D component of fish and fish oils that is important.

I recently saw an elderly lady from Bangladesh living in northwest England. I would have expected her to have a very low blood level of vitamin D, as her exposure to the sun was minimal. However the blood level was 47ng/ml, not 4 as expected. She eats oily fish from Bangladesh every day, showing its value as a source of vitamin D with subsequent good health. I expect her blood levels of omega-3 fatty acids would also be high.

But it is unfashionable vitamin D that is important, not fashionable omega-3.

David Grimes
www.vitamindandcholesterol.com

Excellent point. The health effects of omega-3 and vitamin D are intimately intertwined when examining populations that consume fish.

In this study of Inuits, it is indeed impossible to dissect out how much psychological distress was due to reduced vitamin D, how much due to reduced omega-3s. My bet is that it's both. Thankfully, we also have data examining the use of pure omega-3 fatty acids in capsule (not intact fish) form, including studies like GISSI Prevenzione.

Nonetheless, Dr. Grimes reminds us that both vitamin D and omega-3 fatty acids from fish oil play crucial roles in mental health and other aspects of health, and that it's the combination that may account for the extravagant health effects previously ascribed only to omega-3s.

Beyond its ability to slash risk for cardiovascular events, omega-3 fatty acids from fish oil also reduce triglycerides.

There's no remaining question that omega-3s do this quite effectively. After all, the FDA approved prescription fish oil, Lovaza, to treat a condition called familial hypertriglyceridemia, an inherited condition in which very high triglycerides in the 100s or 1000s of milligrams typically develop.

The omega-3 fraction of fatty acids are unique for their triglyceride-reducing property. No other fraction of fatty acids, such as omega-6 or saturated, can match the triglyceride-reducing effect of omega-3s.

But why does fish oil reduce triglycerides?

First of all, what are triglycerides? As their name suggests, triglycerides consist of three ("tri-") fatty acids lined up along a glycerol (sugar) "backbone." Triglycerides are the form in which most fatty acids occur in the bloodstream, liver, and other organs. (Fatty acids, like omega-3, omega-6, mono- or polyunsaturated, or saturated, rarely occur as free fatty acids unbound to glycerol.) In various lipoproteins in the blood, like LDL, VLDL, and HDL, fatty acids occur as triglycerides.

Of all lipoproteins, chylomicrons (the large particle formed through intestinal absorption of fatty acids and transported to the liver via the lymph system) and VLDL (very low-density lipoprotein, very low-density because they are mostly fat and little protein) particles are richest in triglycerides. Thus, we would expect that omega-3s exert their triglyceride-reducing effect via reductions in either chylomicrons or VLDL.

Indeed, that seems to be the case. The emerging evidence suggests that omega-3 fatty acids from fish oil reduce triglycerides through:

--Reduced VLDL production by the liver (Harris 1989)
--Accelerating chylomicron and VLDL elimination from the blood
--Activation of peroxisome proliferator-activated receptor gamma (PPAR-gamma)--Omega-3s ramp up the cellular equipment used to convert fatty acids to energy (oxidation) (Gani 2008)

Combine omega-3 fatty acids from fish oil with wheat elimination and you have an extremely potent means of reducing triglycerides. Read a previous Heart Scan Blog post here to read how a patient reduced triglycerides 93.5% from 3100 mg/dl to 210 mg/dl in just a few weeks using fish oil and wheat elimination.

For another perspective on omega-3 blood levels, here's an interesting study in northern Quebec Inuits.

Traditionally, Inuits consumed large quantities of omega-3-rich seal, fish, caribou, and whale, even eating the fat. However, like the rest of the world, modern Inuits have increased consumption of store-bought foods, largely processed carbohydrates. Along with this trend has emerged more heart disease, diabetes, and depression.

A group from Laval University and University of Guelph, both in Canada, examined the relationship of plasma EPA + DHA levels and measures of psychological distress. This group had previously shown that Inuits older than 50 years had twice the plasma omega-3 levels (11.5%) compared to those younger than 50 years (6.5%), reflecting the shift away from the traditional diet.

Psychological distress was measured with The Psychological Distress Index Santé-Québec Survey (PDISQS-14): the higher the score, the greater the psychological distress. (In the graphs, tertile 1 is least distressed; tertile 5 is most distressed. Sorry about the small chart graphic--click on the graphic to make it bigger.)

From Lucas M et al 2009 (http://www.nutrasource.ca/NDI/Assets/Articles/Plasma%20omega-3%20and%20psychological%20distress%20among%20Nunavik%20Inuit.pdf)

"Our main finding was that women in the second and third tertiles of EPA+DHA concentrations in plasma PLs [phospholipids] had a 3 times lower risk of having a high-level PD [psychological distress] score than women in the lowest tertile."

While the relationship is stronger for women, you can see that, the higher the EPA + DHA plasma level, the lower the likelihood of psychological distress. Interestingly, the tertile with the greatest distress and lowest EPA + DHA levels had a plasma level of 7.0-7.5%--far higher than average Americans.

(Plasma levels of EPA + DHA were used in this study, which tend to reflect more recent omega-3 intake than the more stable and slower-to-change RBC Omega-3 Index that we use. Plasma levels also tend to run about 10-20% lower than RBC levels.)

Of course, there's more to psychological distress than omega-3 blood levels. After all, eating fish or taking fish oil capsules won't make money worries go away or heal an unhappy marriage. But it is one variable that can be easily and safely remedied.

I answered a page from a hospital nurse recently one evening while having dinner with the family.

RN: "This is Lonnie. I'm a nurse at _____ Hospital. I've got one of your patients here, Mrs. Carole Simpson. She's here for a knee replacement with Dr. Johnson. She says she's taking 12,000 units of vitamin D every day. That can't be right! So I'm calling to verify."

WD: "That's right. We gauge patients' vitamin D needs by blood levels of vitamin D. Carole has had perfect levels of vitamin D on that dose."

RN: "The pharmacist says he can replace it with a 50,000 unit tablet."

WD: "Well, go ahead while Carole's in the hospital. I'll just put her back on the real stuff when she leaves."

RN: "But the pharmacist says this is better and she won't have to take so many capsules. She takes six 2,000 unit capsules a day."

WD: "The 50,000 units you and the pharmacist are talking about is vitamin D2, or ergocalciferol, a non-human form. Carole is taking vitamin D3, or cholecalciferol, the human form. The last time I checked, Carole was human."

RN: (Long pause.) Can we just give her the 50,000 unit tablet?

WD: "Yes, you can. But you actually don't need to. In fact, it probably won't hurt anything to just hold the vitamin D altogether for the 3 days she's in the hospital, since the half-life of vitamin D is about 8 weeks. Her blood level will barely change by just holding it for 3 days, then resuming when she's discharged."

RN: (Another long pause.) Uh, okay. Can we just give her the 50,000 units?"

WD: "Yes, you can. No harm will be done. It's simply a less effective form. To be honest, once Carole leaves the hospital, I will just put her back on the vitamin D that she was taking."

RN: "Dr. Johnson was worried that it might make her bleed during surgery. Shouldn't we just stop it?"

WD: "No. Vitamin D has no effect on blood coagulation. So there's no concern about perioperative bleeding."

RN: "The pharmacist said the 50,000 unit tablet was better, also, because it's the prescription form, not an over-the-counter form."

WD: "I can only tell you that Carole has had perfect blood levels on the over-the-counter preparation she was taking. It works just fine."

RN: "Okay. I guess we''ll just give her the 50,000 unit tablet."

From the alarm it raises trying to administer nutritional supplements in a hospital, you'd think that Osama Bin Laden had been spotted on the premises.

I laugh about this every time it happens: A patient gets hospitalized for whatever reason and the hospital staff see the supplement list with vitamin D, fish oil at high doses, iodine, etc. and they panic. They tell the patient about bleeding, cancer, and death, issue stern warnings about how unreliable and dangerous nutritional supplements can be.

My view is the exact opposite: Nutritional supplements are a wonderful, incredibly varied, and effective array of substances that, when used properly, can provide all manner of benefits. While there are selected instances in which nutritional supplements do, indeed, have interactions with treatments provided in hospitals (e.g., Valerian root and general anesthesia), the vast majority of supplements have none.

Omega-3 fatty acids from fish oil have the capacity to "thin the blood." In reality, omega-3s exert a mild platelet-blocking effect (platelet activation and "clumping" are part of clot formation), while also inhibiting arachidonic acid formation and thromboxane.

But can fish oil cause excessive bleeding?

This question comes up frequently in the office, particularly when my colleagues see the doses of fish oil we use for cardiovascular protection. "Why so much fish oil? That's too much blood thinning!"

The most recent addition to the conversation comes from a Philadelphia experience reported in the American Journal of Cardiology:

Comparison of bleeding complications with omega-3 fatty acids + aspirin + clopidogrel--versus--aspirin + clopidogrel in patients with cardiovascular disease.(Watson et al; Am J Cardiol 2009 Oct 15;104(8):1052-4).

All 364 subjects in the study took aspirin and Plavix (a platelet-inhibiting drug), mostly for coronary disease. Mean dose aspirin = 161 mg/day; mean dose Plavix = 75 mg/day. 182 of the subjects were also taking fish oil, mean dose 3000 mg with unspecified omega-3 content.

During nearly 3 years of observation, there was no excess of bleeding events in the group taking fish oil. (In fact, the group not taking fish oil had more bleeding events, though the difference fell short of achieving statistical significance.) Thus, 3000 mg per day of fish oil appeared to exert no observable increase in risk for bleeding. This is consistent with several other studies, including that including Coumadin (warfarin), with no increased bleeding risk when fish oil is added.

Rather than causing blood thinning, I prefer to think that omega-3 fatty acids from fish oil restore protection from abnormal clotting. Taking omega-3 fatty acids from fish oil simply restores a normal level of omega-3 fatty acids in the blood sufficient to strike a healthy balance between blood "thinning" and healthy blood clotting.

Here are the results from the latest Heart Scan Blog poll:

What is your dose of omega-3 fatty acids, EPA + DHA, from fish oil? (Add up the total content of EPA + DHA per capsules; multiply times number of capsules.)

The 479 respondents answered:

Less than 1000 mg per day
65 (13%)

1000-1999 mg per day
145 (30%)

2000-2999 mg per day
98 (20%)

3000-3999 mg per day
79 (16%)

4000-4999 mg per day
33 (6%)

5000-5999 mg per day
14 (2%)

6000 mg per day or more
45 (9%)

The poll did not discriminate between who has heart disease, who does not; who is taking omega-3 fatty acids for high triglycerides or for reduction of lipoprotein(a) (which requires high doses), or other indications. So variation is to be expected.

We can say that nearly all respondents are likely receiving sufficient omega-3s to impact cardiovascular risk, since the benefits begin just by consuming fish twice per month. I am especially impressed at the proportion of respondents (53%) who take at least 2000 mg per day of EPA + DHA. It's clear that people are really embracing the notion that omega-3 fatty acids pack a real wallop of health benefits.

Because different people in different situations and lipid/lipoprotein patterns have different omega-3 needs, there is really no "right" or "wrong" dose of omega-3 fatty acids.

However, there are several factors that enter into knowing your ideal omega-3 intake:

--Higher triglycerides require higher doses
--Lipoprotein(a) can respond to higher doses
--Having coronary or carotid plaque means you desire a "therapeutic" dose of omega-3s, not just a "preventive" dose

Time is a factor, also: The longer you take omega-3s, the higher your blood levels go. You can accelerate the replacement of non-omega-3s with higher doses of omega-3s.

But too much is not good either. Some participants in Track Your Plaque, for instance, have experimented with very high doses of EPA + DHA in the 9000-10,000 per day range and witnessed dramatic increases in LDL.

Much of the uncertainty about dosing will also be cleared up as we get more experience with the Omega-3 RBC Index, i.e, the proportion of fatty acids in red blood cells that are omega-3s. We are currently aiming for an Omega-3 Index of 10%, given the heart attack reductions observed at this level.

Another in a series of data extrapolations that attempt to predict long-term cancer risk from medical radiation exposure was published in the July 13, 2009 Archives of Internal Medicine, viewable here.

Over the years, I've fussed about the radiation dose used by some centers for CT heart scans. (Note: I'm talking about CT heart scans, not CT coronary angiograms, an entirely different test with different radiation exposure.) In the "old" days, when electron-beam devices (EBT) were the best on the block, the old single-slice CT scanners (the predecessor of the current 64-slice MDCT scanners) exposed patients to ungodly quantities of radiation, while the EBT devices required very small quantities (0.5 mSv or about the equivalent of 4 standard chest x-rays or one mammogram).

But CT technology has advanced considerably. While EBT has been phased out (although it was an exceptional technology, GE acquired the small California manufacturer, then promptly scrapped the operation; you can guess why), multi-detector CT (MDCT) technology has improved in speed, image quality, and radiation exposure.

While it has improved, radiation exposure still remains an issue. The authors of the study applied the scanning protocols used at three hospitals and those in several CT heart scan studies, then calculated radiation exposure. They found a more than ten-fold range of exposure, from 0.8 mSv to 10.5 mSv. (All scanners were MDCT, none EBT.)

That's precisely what I've been worrying about: In the rapid rush to develop new devices, radiation exposure has often been a neglected issue. While some scan centers do an excellent job and take steps to minimize exposure, others barely lift a finger and consequently expose their patients to unnecessary radiation.

However, it's not as bad as it sounds. For one, the study included 16-slice MDCT scanners, a scanner type that I warned people to not use because of radiation. On the current most popular 64-slice devices, much lower radiation exposure is possible, on the order of 0.8-1.2 mSv routinely--if the center takes the effort.

This study, while eye-opening, will achieve some good: CT heart scans are here to stay. But the day-to-day practice of heart scanning should be:

1) standardized
2) conducted with radiation exposure as low as possible, preferably <0.8 mSv

To read more about this issue, below I've reprinted a 2007 full Track Your Plaque Special Report, CT Heart Scans and Radiation: The Real Story.

CT heart scans and radiation: The real story

“My personal opinion is that many patients today who are receiving multiple CT scans may well be getting at least comparable doses to subjects that have now developed malignancies from x-ray radiation received in the 1930s and '40s. And, similar to those days when the doses were unknown, the dose that patients receive today over a course of years of multiple CT scans is also completely unknown . . .

“I recommend that all healthcare providers become familiar with the concept that 1 in 1000 CT studies of the chest, abdomen, or pelvis may result in cancer.”

Richard C. Semelka, MD

Professor and Vice Chairman, Department of Radiology

University of North Carolina–Chapel Hill

Is this just hype to generate headlines? Or is the truth buried in the enormous marketing clout of the medical device industry, among which the imaging device manufacturers reign supreme?

It’s been over 110 years since radiation was first used for medical imaging. Over those years, it has had its share of misadventures.

In the 1930s and 1940s, before the dangers of radiation were recognized, shoe shoppers had shoes fitted using an x-ray device of the foot to assess fit. High doses of radiation were used to shrink enlarged tonsils and extinguish overactive thyroid glands. Attitudes towards radiation were so lax that doctors commonly permitted themselves to be exposed without protection day after day, year after year, until an unexpected rise in blood cancers like leukemia was observed. As recently as the 1970s and 1980s, cancers like Hodgkins’ disease were treated with high doses of radiation, also leading to radiation-induced diseases decades later.

Not all radiation is bad. Radiation can also be used as a therapeutic tool and even today remains a useful and reasonably effective method to reduce the size, sometimes eliminate, certain types of cancer. Forty percent of people with cancer now receive some form of radiation as part of their treatment (Ron E 2003).

Just how much does medical radiation add to our exposure?

Estimates vary, but most experts estimate that medical imaging provides approximately 15% of total lifetime exposure. In other words, radiation exposure from medical imaging is simply a small portion of total exposure that develops over the years of life. Exposure can be much higher, however, in a specific individual who undergoes repeated radiation imaging or treatment of one sort or another.

For all of us, exposure to medical radiation is part of lifetime exposure from multiple sources, added to the radiation we receive from the world around us. Just by living on earth, we are exposed to radiation from space and naturally-occurring radioactive compounds, and receive somewhere around 3.0 mSv per year (U.S. Nuclear Regulatory Commission). (Doses for radiation exposure are commonly expressed in milliSieverts, mSv, a measure that reflects whole-body radiation exposure.) People living in high-altitude locales like Colorado get exposed to an additional 30–50% ambient radiation (1.0–1.5 mSv more per year).

Much of the information on radiation exposure comes from studies like the Life Span Study that, since 1961, has tracked 120,000 Japanese exposed to radiation from the atomic bombs dropped in 1945 (Preston DL et al 2003). Although regarded as a high-dose exposure study for obvious reasons, there are actually thousands of people in this study who were exposed to lesser quantities of radiation (because of distance from the bomb sites) who still display a “dose-response” increased risk for cancer many years later in life. Radiation exposures of as little as 5–20 mSv showed a slight increase in lifetime risk.

Occupational and excessive medical exposure to radiation also provides a “laboratory” to examine radiation risk. Miners exposed to radon gas; patients exposed to the imaging agent, Thorotrast, containing radioactive isotope thorium dioxide and used as an x-ray contrast agent in the 1930s and 1940s and possesses the curious property of lingering in the body for over 30 years after administration; radium injections administered between 1945 and 1955 to treat diseases like ankylosing spondylitis and tuberculosis, all provide researchers an opportunity to study the long-term effects of various types of radiation exposure over many years (Harrison JD et al 2003).

The excess exposure of workers and several hundred thousand nearby residents to the Mayak nuclear plant in Russia has also revealed a “dose-response” relationship, with increasing exposure leading to more cancers, including leukemia and solid cancers of the bone, liver, and lung (Shilnikova NS et al 2003). Nuclear waste released into the Techa river between 1948 and 1956 contaminated drinking water used by over 100,000 Russians. A plant explosion in 1957 also released an excess of radiation into the atmosphere, yielding exposure via inhalation. Some sources estimate that at least 272,000 people have been affected by radiation from the Mayak plant. This unfortunate situation has, however, yielded plenty of data on radiation exposure and its long-term effects.

It’s also been known for several decades that people who receive therapeutic radiation for treatment of cancer, even with the reduced doses now employed, are subject to increased risk of a second cancer consequent to the radiation treatment.

From experiences like this, radiation experts estimate that an exposure of 10 mSv increases a population’s risk for cancer by 1 in 1000 (Semelka RC et al 2007).

This question was recently thrust into the spotlight with publication of a study from Columbia University in New York suggesting that a 20-year old woman would be exposed to a lifetime risk of cancer as high as 1 in 143 consequent to the radiation received during a CT coronary angiogram. (Important note: This was estimated risk from a CT coronary angiogram, not a simple heart scan that we advocate for the Track Your Plaque program.) The risk at the low end of the spectrum would be in an 80-year old man (because of the shorter period of time to develop cancer), with a risk of 1 in 5017. If “gating” to the EKG is added (which many scan centers do indeed perform nowadays), risk for a 60-year old woman is estimated at 1 in 715; risk for a 60-year old male, 1 in 1911 (Einstein AJ et al 2007). This study generated some criticism, since it did not directly involve human subjects, but used “phantoms” or x-ray dummies to simulate x-ray exposure. Nonetheless, the point was made: CT coronary angiograms in current practice do indeed expose the patient to substantial quantities of radiation, sufficient to pose a lifetime risk of cancer.

The media frenzy

The NY Times ran an article called With Rise in Radiation Exposure, Experts Urge Caution on Tests in which they stated:

"According to a new study, the per-capita dose of ionizing radiation from clinical imaging exams in the United States increased almost 600 percent from 1980 to 2006. In the past, natural background radiation was the leading source of human exposure; that has been displaced by diagnostic imaging procedures, the authors said."

“This is an absolutely sentinel event, a wake-up call,” said Dr. Fred A. Mettler Jr., principal investigator for the study, by the National Council on Radiation Protection. “Medical exposure now dwarfs that of all other sources.”

Radiation is a widely used imaging tool in medicine. Although CT scans of the brain, bones, chest, abdomen, and pelvis account for only 5% of all medical radiation procedures, they are responsible for nearly 50% of medical radiation used. It’s been known for years that increasing radiation exposure increases cancer risk over many years, but the boom of newer, faster devices that provide more detailed images has opened the floodgates to expanded use of CT scanners.

But before we join in the hysteria, let's first take a look at exposure measured for different sorts of tests:

Typical effective radiation dose values for common tests

Computed Tomography

Head CT 1 – 2 mSv
Pelvis CT 3 – 4 mSv
Chest CT 5 – 7 mSv
Abdomen CT 5 – 7 mSv
Abdomen/pelvis CT 8 – 11 mSv
Coronary CT angiography 5 – 12 mSv

Non-CT

Hand radiograph Less than 0.1 mSv
Chest radiograph Less than 0.1 mSv
Mammogram 0.3 – 0.6 mSv
Barium enema exam 3 – 6 mSv
Coronary angiogram 5 – 10 mSv
Sestamibi myocardial perfusion (per injection) 6 – 9 mSv
Thallium myocardial perfusion (per injection) 26 – 35 mSv

Source: Cynthia H. McCullough, Ph.D., Mayo Clinic, Rochester, MN

A plain, everyday chest x-ray, providing less than 0.1 mSv exposure, provides about the same quantity of radiation exposure as flying in an airplane for four hours, or the same amount of radiation from exposure to our surroundings for 11–12 days. Similar exposure arises from dental x-rays.

If you have a heart scan on an EBT device, then your exposure is 0.5-0.6 mSv, roughly the same as a mammogram or several standard chest x-rays.

With a heart scan on a 16- or 64-slice multidetector device, exposure is ideally around 1.0-2.0 mSv, about the same as 2-3 mammograms, though dose can vary with this technology depending on how it is performed (gated to the EKG, device settings, etc.)

CT coronary angiography presents a different story. This is where radiation really escalates and puts the radiation exposure issue in the spotlight. As Dr. Cynthia McCullough's chart shows above, the radiation exposure with CT coronary angiograms is 5-12 mSv, the equivalent of 100 or more chest x-rays or 20 mammograms. Now, that's a problem.

The exposure is about the same for a pelvic or abdominal CT. The problem is that some centers are using CT coronary angiograms as screening procedures and even advocating their use annually. This is where the alarm needs to be sounded. These tests, as wonderful as the information and image quality can be, are not screening tests. Just like a pelvic CT, they are diagnostic tests done for legitimate medical questions. They are not screening tests to be applied broadly and used year after year.

It’s also worth giving second thought to any full body scan you might be considering. These screening studies include scans of the chest, abdomen, and pelvis. These scans, performed for screening, expose the recipient to approximately 10 mSv of radiation (Radiological Society of North American, 2007). Debate continues on whether the radiation exposure is justified, given the generally asymptomatic people who generally undergo these tests.

Always be mindful of your radiation exposure, as the NY Times article rightly advises. However, don't be so frightened that you are kept from obtaining truly useful information from, for instance, a CT heart scan (not angiography) at a modest radiation cost.

Heart scans, CT coronary angiograms and the future

Unfortunately, practicing physicians and those involved in providing CT scans are generally unconcerned with radiation exposure. The majority, in fact, are entirely unaware of the dose of radiation required for most CT scan studies and unaware of the cancer risk involved. It is therefore up to the individual to insist on a discussion of the type of scanner being used, the radiation dose delivered (at least in general terms), the necessity of the test, alternative methods to obtain the same diagnostic information, all in the context of lifetime radiation exposure.

Our concerns about radiation exposure all boil down to concern over lifetime risk for cancer, a disease that strikes approximately 20% of all Americans. Many factors contribute to cancer risk, including obesity, excessive saturated fat intake, low fiber intake, lack of vitamin D, repeated sunburns, excessive alcohol use, smoking, exposure to pesticides and other organochemicals, asbestos and other industrial exposures, electromagnetic wave exposure, and genetics. Radiation is just one source of risk, though to some degree a controllable one.

Some people, on hearing this somewhat disturbing discussion, refuse to ever have another medical test requiring radiation. That’s the wrong attitude. It makes no more sense than wearing lead shielding on your body 24 hours a day to reduce exposure from the atmosphere. Taken in the larger context of life, radiation exposure is just one item on a list of potentially harmful factors.

It is, however, worth some effort to minimize radiation exposure over your lifetime, particularly before age 60, and by submitting to high-dose testing only when truly necessary, or when the potential benefits outweigh the risks. Thus, with heart scans and CT coronary angiography, some thought to the potential benefits of knowing your score or the information gained from the CT angiogram need to be considered before undergoing the test. Often the practical difficulty, of course, is that your risk for heart disease simply cannot be known until after the test.

In our view, in the vast majority of instances a simple CT heart scan can serve the simple but crucial role of quantifying risk for heart attack and atherosclerotic plaque. CT heart scans yield this information with less than a tenth of the radiation exposure of a CT coronary angiogram. In people without symptoms and a normal stress test, there is rarely a need for CT coronary angiography with present day levels of radiation exposure. Perhaps as technology advances and the radiation required to generate images is reduced, then we should reconsider.

Early experiences are suggesting that the newest 256-slice scanners, now being developed but not yet available, will cut the dose exposure of 64-slice CT angiograms in half (from 27.8 mSv to 14.1 mSv in a recent Japanese study). The 256-slice scanners will allow scanning that is faster over a larger area in a given period of time.

Thankfully, the scanner manufacturers are increasingly sensitive to the radiation issue and have been working on methods to reduce radiation exposure. However, it still remains substantial.

References:
Einstein AJ, Henzlova MJ, Rajagopalan S. Estimating risk of cancer associated with radiation exposure from 64-slice computed tomography coronary angiography. JAMA 2007 Jul 18;298(3):317–323.

Harrison JD, Muirhead CR. Quantitative comparisons of cancer induction in humans by internally deposited radionuclides and external radiation. Int J Radiat Biol 2003 Jan;79(1):1–13.

Hausleiter J, Meyer T, Hadamitzyky M et al. Radiation Dose Estimates From Cardiac Multislice Computed Tomography in Daily Practice: Impact of Different Scanning Protocols on Effective Dose Estimates. Circulation 2006;113:1305–1310.

Kalra MK, Maher MM, Toth TL, Hamberg LM, Blake MA, Shepard J, Saini S. Strategies for CT radiation dose optimization. Radiology 2004;230:619–628.

Mayo JR, Aldrich J, Müller NL. Radiation exposure at chest CT: A statement of the Fleischner Society. Radiology 2003; 228:15–21.

Mori S, Nishizawa K, Kondo C, Ohno M, Akahane K, Endo M. Effective doses in subjects undergoing computed tomography cardiac imaging with the 256-multislice CT scanner. Eur J Radiol 2007 Jul 10; [Epub ahead of print].

Preston DL, Pierce DA, Shimizu Y, Ron E, Mabuchi K. Dose response and temporal patterns of radiation-associated solid cancer risks. Health Phys 2003 Jul;85(1):43–46.

Ron E. Cancer risks from medical radiation. Health Phys 2003 Jul;85(1):47–59.

Shilnikova NS, Preston DL, Ron E et al. Cancer mortality risk among workers at the Mayak nuclear complex. Radiation Res 2003 Jun;159(6):787–798.

Semelka RC, Armao DM, Elias J Jr, Huda W. Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI. J Magn Reson Imaging 2007 May;25(5):900–9090.

Copyright 2007, Track Your Plaque.

Anne
7/16/2009 11:38:08 AM |

I remember those x-ray devices at the shoe store. It was fun looking at the bones in my feet. I also got to play with mercury when I visited an amateur chemist in the neighborhood. He would pour a little mercury in our hands and we would roll it around.

I wonder what my radiation dose was in the years I was having coronary blockage. I went through 6 coronary caths - 4 were stents. Then I had bypass. Yearly mammograms and dental xrays. Bone density testing every 3 yrs. There are websites where one can add up all their radiation exposure including and estimate of environmental exposure too.

Brate
7/17/2009 5:46:33 AM |

Sometimes for a patient, it is more a comfort than the technology which we generally try to run for. And does it really matter for a heart patient having an artery blockage or having their valves dismantled that what amount of radiation they are incurring. The question is, is there any feasible reason to question the ability of such tests. These tests have been a boon for both doctors to help them diagnose the problems, and for the patients to help them have a better life. But yes, advancements in the technology should be a possible solution. But itâ€™s not always the best solution to the problem. Advancements in the technology have greatly diversified the perception of people towards healthcare. People used to be frightened when they were prescribed for any test, or were forwarded to hospital. But now, because of the amount of advancements in technology and also the amount of soft-care has changed the age-old perception of healthcare. Now, people feel free to have a medical checkup. The amount of comfort they feel though surrounded by some most complex machineries in the world is the achievement that technology has got. The concepts like concierge medicine and Boutique medical practice has revolutionized the basic fundamentals of healthcare. Many hospitals and medical service providers: Cleveland clinic, Mayo Clinic, Elite health, to name a few, have completely revolutionized the concept of older concierge medicine. The amount of care added with treatment makes a trip to hospital a better journey. All the requirements starting from transportation, stay in the hotel, appointments, etc are one phone away with these concierge plans. Increasingly people are opting for concierge facilities. The overall information regarding concierge plan is described here:
https://www.clevelandclinic.org/thoracic/Concierge/Concierge.htm
http://www.mayoclinic.org/travel-rst/concierge-services.html
http://www.elitehealth.com/concierge_healthcare.php

buy jeans
11/3/2010 4:57:15 PM |

However, it's not as bad as it sounds. For one, the study included 16-slice MDCT scanners, a scanner type that I warned people to not use because of radiation. On the current most popular 64-slice devices, much lower radiation exposure is possible, on the order of 0.8-1.2 mSv routinely--if the center takes the effort.

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