Impact of thyroid gland on health
The thyroid gland produces hormones responsible for the body metabolism. Thyroid function is precisely regulated by higher brain structures, in order to avoid hyperactivity (hyperthyroidism) or underactivity (hypothyroidism). Thyroid function can be slightly disturbed without any symptom or sign, also known as subclinical thyroid dysfunction. This dysfunction affects 8-18% of adults over 65 years, especially women. Overt hyperthyroidism (with symptoms) is known to have long-term complications such as cardiac arrhythmia or osteoporosis, but long-term risks of subclinical hyperthyroidism were unclear.

A study of 52,674 adults on 4 continents
With the support of the Swiss National Science Foundation, a team of researchers led by Prof. Dr. med. Nicolas Rodondi from Inselspital, Bern, analyzed data of 52,674 participants from 10 prospective cohorts in the United States, Europe, Brazil and Australia to assess long-term risks of subclinical hyperthyroidism. After a follow-up of over 8 years, subclinical hyperthyroidism was associated with a 25% increase of mortality from coronary heart disease or any other cause, and with 65% increase of atrial fibrillation.

Should we screen and treat subclinical hyperthyroidism?
These findings are consistent with recent international treatment guidelines stating that treatment of subclinical hyperthyroidism should be considered for adults over 65 years and in patients with cardiac disease. However, further clinical studies are needed to prove treatment efficacy and whether subclinical thyroid dysfunction should be screened in the general population. These studies are currently ongoing in France and in a European trial among 3000 older adults, with the participation of Inselspital, Bern, possibly with other Swiss hospitals in the near future.

Subclinical hyperthyroidism and the risk of coronary heart disease and mortality

Author audio interview with Dr. Nicolas Rodondi and Kenneth D Burman