257. Thyroid function tests in patients with seasonal affective disorder and control subjects

Abstract

Seasonal affective disorder (SAD) is a condition of recurring winter depressions alternating with non-depressed periods in spring and summer. Because some symptoms of SAD, such as decreased energy and weight gain, also occur in hypothyroidism, it is possible that individuals with SAD have a subtle decrease in thyroid function. Multiple lines of evidence suggest that changes in function of the hypothalamo-pituitary-thyroid axis could be responsible for seasonal changes in behavior and physiology. Studies of thyroid function might help to clarify the biological mechanisms involved in the pathogenesis of SAD and seasonality. We studied blood levels of free thyroxine (T4) and thyroid-stimulating hormone (TSH) in 75 SAD patients and 74 matched controls in the winter. Subjects with overt hypothyroidism were excluded from the study population. We found that levels of free T4 were significantly lower in patients than in normal volunteers, but that there was no difference in TSH levels between SAD patients and healthy volunteers. Future research will be needed to clarify the role of the hypothalamo-pituitary-thyroid axis in the pathogenesis of winter depression. Specifically, it will be important to determine whether the difference in thyroid function between SAD patients and controls, if replicated, is an epiphenomenon or is related to the biological mechanisms that cause some of the symptoms of SAD.