Seasonal Affective Disorder (SAD) is characterised by lowered mood and atypical
depressive symptoms such as hypersomnia, weight gain and fatigue. These
symptoms seem associated with hypothyroidism, but the results of evaluations of
the thyroid function in SAD patients have been conflicting, most likely due to
the very small number of observations.
In total, 83 patients
fulfilling the DSM-III-R criteria for SAD were treated with bright light for 1
week in an open trial. Thyroid function was evaluated by TSH
(thyroid-stimulating hormone), T(4) (thyroxine) and T(3) (triiodthyronine)
levels at baseline and after 1 week of bright light treatment.
The response rate in
terms of a 50% reduction of pre-treatment scores on the Hamilton Depressions
Rating Scale (HAM-D(17)) was 61%. The TSH levels in all 83 patients decreased significantly
from 1.57 at baseline to 1.30 at endpoint. In the group of responders (n=52)
the TSH levels decreased significantly from 1.71 to 1.37, while in the group of
non-responders (n=31) the decrease in TSH levels was not statistically
During 1 week of bright
light therapy the TSH levels in SAD patients were reduced, with the highest
reduction in the group of patients responding to light therapy.