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Does iodine deficiency contribute to plaque growth?
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Thyroid status is proving to be a crucial facet of the Track Your Plaque program.

In this Special Report we review iodine’s neglected role in thyroid health, and thereby heart health. This is supplemented by an interview with epidemiologist, trace mineral

and iodine expert, Dr. Stephen Hoption Cann.

Dr. Hoption Cann is author of the 2004 paper, Hypothesis: Dietary Iodine Intake in the Etiology of Cardiovascular Disease

In this important paper, Dr. Hoption Cann reviews the several decades of obscure - and much forgotten - clinical and scientific literature that makes a compelling argument for the critical connection between iodine and heart health.

Before we turn to Dr. Hoption Cann’s important observations, let’s discuss some background on iodine.

Iodine: Disinfectant, antioxidant, essential nutrient . . . coronary preventive agent?

Iodine: Yes, the same peculiar purple-brown liquid your mother applied to a scraped knee. Mom knew of iodine’s anti-infective properties. But perhaps she was unaware of its potent anti-oxidative properties, its ability to sterilize drinking water, its radio-opaque quality (making it suitable for use as a contrast agent for x-ray), its necessity for thyroid function.

Paleontologists believe that iodine was the first protective anti-oxidant employed by primitive organisms exposed to the developing oxygenated world. Iodine became concentrated in the oceans, providing iodine to coastal regions. Areas away from the coasts, or never covered with oceans, contain little or no iodine. There is even a fascinating theory that Neanderthals were an iodine-deficient inland form of primate that resemble modern iodine-deficient humans, or “cretins”; the survival disadvantage of iodine deficiency permitted iodine-replete (due to better access and a theorized genetic alteration that made iodine retention more efficient) coastal primates (now called “early modern humans,” formerly “Cro-Magnon”) to replace Neanderthals. The ability to gain access to and efficiently retain iodine may therefore have played a crucial role in human evolution.

Turn-of-the-last-century America was plagued with goiter, an unsightly enlargement of the thyroid gland visible on the front of the neck. As many as a third of the inhabitants of some parts of the country (e.g., the Great Lakes, AKA the “goiter belt,” and much of the Midwest) were affected. The connection between goiter and deficiency of iodine wasn’t made until a family doctor in Cleveland, Ohio, conducted a homespun experiment on schoolgirls in a nearby community in 1916. Despite objections from local residents, Dr. David Marine administered what we now recognize as a very large dose of iodine: 170-340 mg (170,000 – 340,000 micrograms, mcg) sodium iodide per day to 900 girls. Virtually none of the girls receiving iodine supplementation developed goiters, compared to 22% of the control group not receiving iodine (Zimmerman MB 2008).

Mothers from the same era, often deficient in iodine, gave birth to severely impaired babies afflicted with far below average intelligence, consigned to a brief, disabled life. These children were known by the harsh name of “cretins,” the disease known as “cretinism.”

The recognition of the importance of iodine launched it into the realm of public health, too large an issue to leave to individuals, families, or physicians to remedy on their own. Much debate ensued in the mid-twentieth century on how to best ensure that the U.S population receive a minimum quantity of iodine in their diets. Table salt (sodium chloride) became the agreed vehicle for iodine in 1924, though iodization was deemed voluntary, not mandatory.

During the 1960s and 70s, most Americans willingly complied by liberally shaking the salt shaker over anything and everything. Overt iodine deficiency largely became a thing of the past, goiters a rarity. FDA guidelines suggest iodine content in salt of 45 mg/kg; this means that slightly over one half teaspoon of salt per day, or 3000 mg (1,150 mg sodium), provides the Recommended Daily Allowance of iodine of 150 mcg per day.

Coincident with the widespread application of the salt shaker was the recognition of the dangers of hypertension. Clinical studies made it clear that liberal use of salt increased blood pressure, fluid retention, even osteoporosis.

The public health message reversed its focus and began to urge reducing use of table salt. Salt use was demonized as the cardiovascular dangers of hypertension gained public recognition. Somehow, the issue of iodine was forgotten. (This has created some peculiar public health collisions. While the American Heart Association advises reduction of salt use, and the American Medical Association has even urged the FDA to remove salt from the “generally recognized as safe” designation, others like UNICEF and the charitable International Council for the Control of Iodine Deficiency Disorders both advocate for increased salt use worldwide.)

Fast forward to the 21st century and many health-conscious people proudly declare their assiduous avoidance of salt, certainly iodized table salt. Others have turned to alternative preparations of sodium chloride, such as sea salt (very little iodine content), Kosher salt (no iodine), and potassium chloride-based salt substitutes (no iodine).

So what’s become of the iodine?

Maybe your iodized salt isn’t so iodized

Even people who use iodized salt are getting less iodine than expected.

Iodine deficiency is on the rise. The NHANES data of Americans’ health has revealed a quadrupling of iodine deficiency in the period between 1971 and 1992, with 11% of the population now clinically iodine deficient as judged by urinary levels of iodine (Hollowell JG et al 1998). Regional variation in incidence seems to have been smoothed over, with no specific areas of the country standing out more than others, unlike the past (likely due to the globalization of the food supply).

A recent study (Dasgupta PK et al 2008) suggests that, even among people who use the salt shaker for cooking and food, daily iodine intake is only around 45 mcg per day. Interestingly, a detailed analysis of several brands of commercially-available salt showed that, after opening, iodine is lost rapidly from the product, especially if stored in humid conditions (see figure); within 10-20 days after opening, iodine content is dramatically reduced, even nearly gone, under conditions of high humidity. Their analysis also showed that, even if the salt is labeled “iodized,” it usually contains substantially less than the FDA-suggested 45 mg/kg.

Loss of iodine over time with exposure to air with specified humidity levels, no light, 22 +/- 1 °C.

From Dasgupta PK et al 2008.

The majority of salt used in processed foods is not iodized. While dairy products and baked foods (bread and related products) were formerly substantial sources of iodine, iodine content of these foods has dropped 70% over the past 20 years due to changing practices by dairy producers and bakers (Dasgupta PK et al 2008). Add to this the currently popular notion of “buy local” and we might therefore expect to see regions with greater proportions of their population with goiter, much as in the early 20th century.

In short, even people who are using iodized table salt and eat common processed foods may not be getting the iodine content they need. In addition, the public health message to limit salt use is accelerating a gradual and insidious return of iodine deficiency.

Iodine deficiency is inevitably followed by underactive thyroid function, reductions in thyroid hormone levels and hypothyroidism. Ironically, we might predict that iodine deficiency is apt to primarily afflict the health conscious, the people most likely to avoid salt and follow the “buy local” practice.

So history repeats itself.

What quantity of iodine is necessary for ideal health?

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