JAMA / Archives – Women with increasing levels of TSH (thyrotropin) within the normal range appear to have a higher risk of fatal coronary heart disease, according to a report in the April 28, 2008 issue of the Archives of Internal Medicine.

Thyrotropin, or TSH, a hormone produced by the pituitary gland, is released into the blood and acts on the thyroid gland to stimulate its growth and function, according to background information in the article. “Emerging evidence indicates that levels of thyrotropin within the reference [normal] range are positively and linearly associated with systolic [top number] and diastolic [bottom number] blood pressure, body mass index and serum lipid concentrations with adverse effects on cardiovascular health.”

Bjørn O. Åsvold, M.D., of the Norwegian University of Science and Technology, Trondheim, Norway, and colleagues studied the association between thyrotropin levels and fatal heart disease in 17,311 women and 8,002 men without known thyroid disease, cardiovascular disease or diabetes at the beginning of the study.

During follow-up, 228 women (1.3 percent) and 182 men (2.3 percent) had died of coronary heart disease. “Of these, 192 women and 164 men had thyrotropin levels within the clinical reference range of 0.5 milli-international units per liter to 3.5 milli-international units per liter,” the authors write. “Overall, thyrotropin levels within the reference range were positively associated with coronary heart disease mortality; the trend was statistically significant in women but not in men.”

“This study shows that coronary heart disease mortality increases in women with increasing levels of thyrotropin within the reference range,” the authors conclude. “These results indicate that relatively low but clinically normal thyroid function may increase the risk of fatal coronary heart disease” (Arch Intern Med. 2008;168[8]:855-860).

Editorial note – Talking about TSH levels can be confusing for patients initially. Simply speaking, TSH is not a thyroid hormone, but a pituitary hormone that tells the thyroid gland to make more thyroid hormone because the body’s level of thyroid hormone (T4, T3) is being perceived by the body as not yet optimal for that particular person. Many endocrinologists have suspected that a “high normal” TSH (closer to 3.5 than 1.0) may often mean a suboptimal thyroid hormone level for a particular person, and this study supports that notion, at least for women.

Remember that a so-called “normal” lab value is usually any value that falls within 2 standard deviations from the mean in a group study. But an individual patient is not a group, and it seems that in the case of TSH what is normal for the group – the reference range – may not be normal or optimal for a particular person. If you are a woman having ongoing problems with obesity, serum lipids, or metabolic syndrome along with a “high normal” TSH, you may want to consider asking your primary care provider for a referral to an endocrinologist to carefully review your thyroid and metabolic status – Dr. Z.