Circadian profiles of cortisol, prolactin, and thyrotropin in seasonal affective disorder

To determine whether circadian profiles of various plasma hormones are abnormal in patients with winter seasonal affective disorder (SAD), we obtained 24-hour profiles of plasma cortisol, prolactin, and thyrotropin in subsets of a sample of 22 depressed patients with SAD on and off light therapy and in subsets of a sample of 24 normal controls. Cortisol levels did not differ between patients and controls, and levels in patients were not affected by light therapy. Prolactin levels were lower in patients than in controls throughout the day (p < 0.03) but were unaffected by light therapy. Independent of patient vs. control status, prolactin levels were higher in women than in men throughout the day (p < 0.003). Thyrotropin levels were no different in patients and controls, but levels in patients were lower following light therapy (p < 0.05).