Prevalence of thyroid antibodies among healthy middle-aged women. Findings from the thyroid study in healthy women.

Autoimmune thyroiditis is the most common cause of subclinical hypothyroidism in North America, is more common in women than men, and is a risk factor for the development of coronary heart disease (CHD). We measured thyroid-stimulating hormone (TSH) and two thyroid antibodies, thyroid peroxidase and thyroglobulin, in stored sera of the participants (aged 44 to 54 years) of the Healthy Women Study. We selected 254 samples from the premenopausal baseline examination in 1983 to 1985 and from a follow-up examination that occurred an average of 5.7 years later (range, 3 to 7.7 years). At follow-up, 95 women remained premenopausal, 98 had ceased menstruating for at least 12 months, and 61 were taking postmenopausal hormone therapy. Overall, the prevalence of the thyroid antibodies in this healthy population was high at both time points (21 to 26%). Women with antibodies had higher TSH concentrations than did those with no antibodies (2.68 +/- 1.3 versus 1.51 +/- .73 mU/L, P < 0.001); this relationship was statistically significant even after excluding those with subclinical hypothyroidism (TSH > 6.0 mU/L). TSH and antibody levels did not differ by menopausal status or hormone therapy use at follow-up. Given the high prevalence of thyroid antibodies among healthy middle-aged women, long-term follow-up is warranted to ascertain whether the presence of antibodies is associated with subsequent excess risk of disease, in particular, CHD.