Thyroid function starting at age 50 tied to life expectancy

Last Updated: 2017-09-18

By Anne Harding

NEW YORK (Reuters Health) - Low-normal thyroid function is associated with longer life expectancy in middle-aged people, according to data from The Rotterdam Study.

"At age 50, people with low-normal thyroid function live up to 3.5 years longer than those with high-normal thyroid function. Also, people with low-normal thyroid function live a longer life without cardiovascular disease (CVD) than those with high-normal thyroid function," Dr. Arjola Bano of Erasmus Medical Center in Rotterdam, the Netherlands, told Reuters Health by email.

Current reference ranges for thyrotropin and free thyroxine (FT4) are based on the 2.5th and 97.5th percentiles in a healthy population, Dr. Bano and colleagues note in their September 18 online report in JAMA Internal Medicine. But they add that studies showing effects of subclinical thyroid dysfunction on cardiovascular disease, mortality, and other outcomes suggest this "arbitrary approach" needs to be re-evaluated.

The researchers looked at Rotterdam Study data on 7,785 men and women age 50 or older (mean age, 65). During a median follow-up of 8 years, 789 incident CVD events and 1,357 deaths occurred.

Men and women in the highest thyrotropin tertile lived 2 and 1.4 years longer, respectively, than those in the lowest tertile. They also lived 1.5 and 0.9 years longer, respectively, without CVD.

Men and women in the highest FT4 tertile, in contrast, lived 3.2 and 3.5 fewer years, respectively, than those in the bottom tertile, while their CVD-free life expectancies were 3.1 and 2.5 years shorter.

Thyroid overactivity is known to be harmful, Dr. Bano and colleagues note, and is associated with increased heart rate, myocardial contractility and hypercoagulability, all of which are related to CVD and mortality.

High thyroid hormones may also boost oxygen consumption and reactive oxygen species production, and "can affect cognition, nerve condition, and bone mineral density, thus contributing to an increased risk of dementia, polyneuropathy, osteoporosis and death," they write. In contrast, low-normal thyroid function may "represent a heritable phenotype of exceptional longevity."

The Rotterdam Study previously found that low-normal thyroid function was associated with an increased risk of diabetes or non-alcoholic fatty liver disease, while high-normal thyroid function was linked to an increased risk of atrial fibrillation or dementia, Dr. Bano noted. "The challenge for future research will be to integrate the associated risk of relevant adverse outcomes, in order to eventually define the clinically relevant normal ranges of thyroid function," she said.

"Our study included mainly white participants," Bano added. "Therefore, it would be informative to further investigate the association of thyroid function with life expectancy in other ethnic groups. Future studies are also needed to elucidate the exact mechanisms underlying the differences in life span within the reference range of thyroid function."

SOURCE: http://bit.ly/2w41ga2

JAMA Intern Med 2017.