There's no doubt that low thyroid function results in fatigue, weight gain, hair loss, along with rises in LDL cholesterol and other fractions of lipids. It can also result in increasing Lp(a), diabetes, and accelerated heart disease, even heart failure.
But how do we distinguish "normal" thryoid function from "low" thyroid function? This has proven a surprisingly knotty question that has generated a great deal of controversy.
Thyroid stimulating hormone, or TSH, is now the most commonly used index of the adequacy of thyroid gland function, having replaced a number of older measures. TSH is a pituitary gland hormone that goes up when the pituitary senses insufficient thyroid hormone, and a compensatory increase of thyroid hormone is triggered; if the pituitary senses adequate or excessive thyroid hormone, it is triggered to decrease release of TSH. Thus, TSH participates in a so-called "negative feedback loop:" If the thyroid is active, pituitary TSH is suppressed; if thyroid activity is low, pituitary TSH increases.
An active source of debate over the past 10 years has been what a normal TSH level is. In clinical practice, a TSH in the range of 0.4-5.0 mIU/L is considered normal. (Lower TSH is hyperthyroidism, or overactive thyroid; high TSH is hypothyroidism, or underactive thyroid.)
The data from a very fascinating and substantial observation called the HUNT Study, however, is likely to change these commonly-held thyroid "rules."
In this study, over 30,000 Norwegians without known thyroid disease were enrolled. TSH levels and lipid (cholesterol) levels were measured.
In this large and extraordinary observation, increasing TSH levels were associated with increasing levels of LDL cholesterol and triglycerides, and decreasing HDL. At what level of TSH did this relationship start? At TSH levels as low as 1.0!
In other words, there were perturbations in standard lipid measures even with TSH levels ordinarily regarded as "normal," even "perfect."
A subsequent observation from the HUNT Study was even more recently published:
Background Recent studies suggest that relatively low thyroid function within the clinical reference range is positively associated with risk factors for coronary heart disease (CHD), but the association with CHD mortality is not resolved.
Methods In a Norwegian population-based cohort study, we prospectively studied the association between thyrotropin levels and fatal CHD in 17 311 women and 8002 men without known thyroid or cardiovascular disease or diabetes mellitus at baseline.
Results During median follow-up of 8.3 years, 228 women and 182 men died of CHD. Of these, 192 women and 164 men had thyrotropin levels within the clinical reference range of 0.50 to 3.5 mIU/L. Overall, thyrotropin levels within the reference range were positively associated with CHD mortality (P for trend = .01); the trend was statistically significant in women (P for trend = .005) but not in men. Compared with women in the lower part of the reference range (thyrotropin level, 0.50-1.4 mIU/L), the hazard ratios for coronary death were 1.41 (95% confidence interval [CI], 1.02-1.96) and 1.69 (95% CI, 1.14-2.52) for women in the intermediate (thyrotropin level, 1.5-2.4 mIU/L) and higher (thyrotropin level, 2.5-3.5 mIU/L) categories, respectively.
Conclusions Thyrotropin levels within the reference range were positively and linearly associated with CHD mortality in women. The results indicate that relatively low but clinically normal thyroid function may increase the risk of fatal CHD.
In other words, the findings of this substantial observation suggest that the ranges of TSH usually regarded as normal contribute to coronary events, cardiac death, as well as lipid patterns. While several other studies have likewise shown a relationship of higher TSH/lower thyroid function with lipid abnormalities and overt heart disease, no previous study has plumbed the depth of TSH to this low level and to such a large scale.
I believe that these findings are enough cause to begin thinking seriously about monitoring thyroid function more seriously to uncover "borderline" TSH increases in the "normal" range. While higher TSH levels predict cardiovascular events, does thyroid replacement at these levels reduce it? Critics will say it's a big leap, but I think that it is worth at least considering.
Stay tuned for a lengthy Special Report followed by a full booklet on these issues on the www.cureality.com website.
Tne Philadelphia NBC affiliate's website carried this commentary from a colleague of mine:
Mark from the Lehigh Valley is curious about scans that can detect heart disease.
He asked, "I am in my early 50s. My father had a heart attack in his 40s. I am healthy with no symptoms of heart disease, should I consider a heart scan?"
"Well, Mark, occasionally family history needs to be considered more closely. If your father had coronary disease at a relatively young age at the absence of any known risk factor for heart disease for example diabetes, smoking, obesity, high blood pressure, than your level of risk should be considered more closely," Dr. Kevin Shinal, a cardiologist, said.
"There are a number of studies available to access [sic] your level of risk. One such study is a calcium score. A calcium score is a form of a CAT scan that access [sic] the calcium burden or presence of calcium in your coronary arteries. It assigns you a score and score is translated into a level of cardiovascular risk," Shinal said.
But the doctor warned because Mark doesn't have active symptoms, the scan probably wouldn't be covered by insurance.
Was there an understandable answer in there? I certainly couldn't find it.
Why pick on some yokel responding inarticulately to the local media's quest for content? Because this is, all too often, what the public hears: Ill-informed blather from someone who has little or no understanding of the issues. Maybe this doctor wanted his practice group to get some free publicity. "Doctor, could you just answer a few questions from viewers?"
Unfortunately, it's not just local media who are guilty of consulting with know-nothings with only passing knowledge of an issue. National media are guilty of it, too. The need to fill airtime with content is better filled with talking heads who present a compelling story, whether or not it is accurate or insightful, rather than an expert with deep insight into a topic who might not present as pretty a story. I've seen this countless times. A good portion of my day, in fact, is occupied responding to patient questions based on the misinformation presented in some media report.
My message of this brief rant: Be very careful of the messages delivered by the media, even if provided by some supposed "expert." In fact, I regard "experts" in health about as believable as politicians. Sure, sometimes they provide accurate information. But they often do not, or provide information with limited understanding. Or, worse, information intended to serve some hidden agenda.
Were the media to ask me to respond to the question, however, I would say:
"Yes, you should absolutely have a heart scan--yesterday! With your family history, there is no other way to accurately, easily, and inexpensively quantify the amount of coronary atherosclerosis in your heart's arteries. A stress test only uncovers advanced disease. A heart catheterization is overkill and absolutely not indicated in an asymptomatic man. Judging the presence of heart disease from cholesterol values is folly.
"What's left? A CT heart scan. So, yes, you need a CT heart scan ASAP with no doubt whatsoever."