Subclinical hypothyroidism is associated with an increased risk of congestive heart failure among older adults, but not with other cardiovascular events and death.
The study is published in the Archives of Internal Medicine.
Subclinical hypothyroidism refers to patients who have an elevated level of the hormone thyrotropin, also known as thyroid stimulating hormone ( TSH ), and a normal level of the hormone thyroxine ( T4 ).
The prevalence of subclinical hypothyroidism increases with age, and is about ten percent in women over the age of 70, and somewhat lower in men.
Subclinical hypothyroidism has been associated with higher levels of some cardiovascular risk factors, but data on cardiovascular outcomes and death are limited.
Nicolas Rodondi, of the University of California, San Francisco, and colleagues studied 2,730 men and women, aged 70 to 79, to determine whether subclinical hypothyroidism was associated with congestive heart failure ( CHF ), coronary heart disease ( CHD ), stroke, peripheral arterial disease ( PAD ), death, and cardiovascular-related death.
Subclinical hypothyroidism was defined as TSH levels of 4.5-6.9 mIU/L ( mild ), 7.0-9.9 mIU/L ( moderate ), and 10 mIU/L or greater ( severe ).
The authors found that the incidence of CHF during a four-year follow-up period was significantly increased in patients with moderate and severe subclinical hypothyroidism, but not in patients with mild subclinical hypothyroidism, who comprised the highest percentage ( 68 percent ) of all patients with subclinical hypothyroidism in the study.
" In this population-based study of older adults, subclinical hypothyroidism was associated with a higher rate of incident and recurrent CHF among participants with a TSH level of 7.0 mIU/L or greater compared with euthyroid participants," they write. " This association persisted after adjustment for cardiovascular risk factors."
" We found no consistent evidence that subclinical hypothyroidism was associated with CHD events, stroke, PAD, cardiovascular-related mortality, or total mortality," they continue.
" Because no other prospective study has assessed the risk of CHF events in subjects with subclinical hypothyroidism, to our knowledge, our results should be confirmed in other large prospective studies, including those in younger populations," the authors conclude. " Further investigation is also warranted to assess whether subclinical hypothyroidism causes or worsens pre-existing heart failure."
Source: American Medical Association, 2005