Thyroid and Your Risk for Heart Disease

Researchers from Norway examined the effect of TSH on heart disease risk

Heart illustration

Research has shown that overt hypothyroidism ––  low thyroid levels –– and hyperthyroidism –– high thyroid levels –– are linked to an increased risk of coronary heart disease (CHD).  CHD occurs when plaque builds up inside of the coronary arteries, thereby depriving your heart of oxygen-rich blood. A study conducted in Norway took this research one step further and looked at the effect normal thyroid levels have on the risk of fatal heart disease.

Examining TSH and CHD Risk

More than 25,000 people were included in the study. The study participants were grouped into five different categories according to their thyroid stimulating hormone (TSH) level:

  • TSH: less than 0.50
  • TSH: 0.50 to 1.4
  • TSH: 1.5 to 2.4
  • TSH 2.5 to 3.5
  • TSH: 3.6 and higher

For the purposes of the study, the TSH reference range was defined as 0.50 to 3.5 mIU/L. (Note: The reference range for laboratories in the United States is typically much wider and runs from approximately 0.50 to 5.5mIU/L. Since 2002, some endocrinologists have recommended that the level be narrowed to a range of 0.30 to 3.0.) Typically, TSH below .50 indicates hyperthyroidism. Anything above 5.5 (for standard guidelines) is indicative or hypothyroidism. 

During the more than eight-year follow-up of the study, 228 women (1.3 percent) and 182 men (2.3 percent) died of coronary heart disease. Of these, 192 women and 164 men had TSH levels within the reference range the researchers used for this study.

The 0.50 to 1.4 TSH range was used as the baseline control group, and as TSH levels rose into the ranges higher than 1.4, the "hazard ratio," which in this case estimated the relative risk of fatal coronary heart disease, also rose in women. (While there was some rise for men, it was not enough to be considered statistically significant.)

The analysis was repeated in another follow-up two years later, and the findings were again consistent with the initial research.

Ultimately, the researchers concluded that there is a clear connection between low –– but clinically normal –– thyroid function in women and fatal coronary heart disease.

The researchers reported that, to their knowledge, there have not been any clinical trials to determine if thyroid hormone replacement might help protect against coronary heart disease. They did note, however, that other research has shown that thyroid hormone replacement treatment may improve cholesterol levels, improve endothelial function (a measure of vascular disease) and reduce other signs of atherosclerosis.

What Does This Mean for the Public?

Certainly, these findings make it especially important that further gender-specific studies be conducted, with a goal of determining if thyroid hormone replacement for people with TSH levels above 1.4 will reduce the risk of fatal coronary heart disease.

Further studies would be of great importance as women are more likely to develop thyroid disease and heart disease is the leading cause of death for women. 

Given that we already know that thyroid hormone replacement can improve various markers for heart disease, there is increasing evidence that the endocrinology and laboratory community need to​ ​finally come to some agreement over adopting the recommended narrower reference range. Lowering the reference range can help people access thyroid medication sooner rather than later. 

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Article Sources
  • Åsvold, Bjørn MD; et. al. "Thyrotropin Levels and Risk of Fatal Coronary Heart Disease: The HUNT Study," Arch Intern Med. 2008;168(8):855-860.