Diurnal and seasonal variations in cortisol, prolactin, TSH and thyroid hormones in women with and without seasonal affective disorder

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Abstract
Women with and without seasonal affective disorder (SAD) were studied on two winter days separated by a week of light treatment (LT) at 2500 lux either in the morning (0800–1000h; 8 patients and 4 controls) or afternoon (1600–1800 h; 5 patients and 3 controls), and on a summer day (7 patients of the morning subgroup and 7 controls). Blood samples were drawn at 4‐h intervals beginning at 0800 h until either 0000 h (7 controls and 6 patients) or until 0400 h of the next day (7 patients of the morning group). Serum samples were assayed for cortisol (COR), prolactin (PRL), thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4) and thyroxine‐binding globulin (TBG). The circadian patterns of three hormones ‐ TSH, COR and PRL ‐ were normal and similar in all groups, and did not alter either by LT or change in season. After LT diurnal mean of TSH levels increased significantly in patients and non significantly in controls. In controls other hormones levels either increased significantly (T3) or showed the tendency towards increase (COR, PRL, T4), while in patients T3, T4 and TBG levels either decreased or remain lower than in controls. Therefore, following LT the levels of thyroid hormones in patients became significantly lower than in controls. No significant seasonal variations in diurnal means of the hormones were found either in patients or in controls. A thyroid malfunction seems to be a trait marker of winter SAD. We also suggest that circadian phase alteration is not of main importance in SAD pathogenesis and effect of LT.