Thyroid Function and Heart Health: A Look at The Research

Monday, January 24, 2011

By Laura Firetag, ND Student, Bastyr University

Learning human physiology over the many years of my academic career has taught me that when one process changes in the body, it always affects many other processes. Adept clinicians know this is especially true of the thyroid gland.

Apparently, a slight change in thyroid function might have a profound effect on our vascular system. While research has documented a clear correlation between subclinical hypothyroidism, hypercholesterolemia and atherosclerosis, research has yet to find a clear connection between subclinical hypothyroidism and coronary heart disease. Both hypercholesterolemia and atherosclerosis are risk factors for coronary heart disease so it makes sense that if a patient has subclinical hypothyroidism they should also be more likely to have coronary disease (CHD) since they are more likely to have the risk factors associated with CHD.

In order to explore the potential correlation, several doctors formed the Thyroid Studies Collaboration and recently published a study-level meta-analysis of prospective cohort studies that measured TSH and T4 levels in participants as well as total mortality and CHD outcomes. The definition of subclinical hypothyroidism itself is somewhat controversial and the collaborators decided to use the definition from the Cardiovascular Health Study. They defined subclinical hypothyroidism as a serum TSH level of 4.5mIU/L to 19.9mIU/L with a normal thyroxine (T4) concentration. The outcomes that were measured included CHD events, CHD mortality and total mortality. After statistical analysis, the Thyroid Studies Collaboration determined that subclinical hypothyroidism was associated with an increased risk of CHD events and CHD mortality but not of total mortality in those patients with higher TSH levels. There was an especially significant increase in CHD risk in patients with TSH levels of 10mlIU/L or more. The correlation remained significant even after the data was adjusted for traditional cardiovascular risk factors.

Based on the results of this meta-analysis, it is easy to conclude that everyone who has a TSH level of 10mlIU/L or more should be treated as though they have hypothyroidism. Unfortunately, the only way to be certain that treating subclinical hypothyroidism is beneficial is to conduct an appropriately powered, well designed double-blind placebo-controlled randomized clinical trial and measure outcome. Subclinical hypothyroidism is quite common; as a doctoral student of naturopathic medicine I hope such a study design is currently underway to assist future clinicians in arriving at a more definitive answer for their patients.

The authors do mention a couple of studies that hint that subclinical hypothyroidism should be taken more seriously. Apparently, ‘one randomized controlled trial has shown benefits with thyroxine treatment of subclinical hypothyroidism on intima-media thickness and another has shown benefits with thyroxine treatment of subclinical hypothyroidism on brachial artery endothelial dysfunction.’

Even if research has yet to definitively show that subclinical hypothyroidism should be treated, it is important that you and your patients get the whole food nutrition necessary for optimal thyroid function. There are also several botanicals that are known to gently support the thyroid gland without creating any physiological imbalances. By supporting your thyroid, you just might also be supporting your heart!!

JAMA. 2010;304(12):1365-1374.

posted by Innate Response at

7:15 AM

Thyroid Function and Heart Health: A Look at The Research

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