A study conducted by Gloth, Alam, and Hollis (1999) was designed to test the hypothesis that vitamin D deficiency might play a role in seasonal affective disorder. This prospective, randomized controlled trolled trial was conducted in a group of 15 participants with seasonal affective disorder. Eight participant received high-dose vitamin D (100,000 UI) and 7 receiving light therapy. All participants receiving vitamin D improved in all outcome measure. The light therapy group showed on significant change in depression measure. Vitamin D status improved in both group (74% vitamin D group: 36% light therapy) Improve in vitamin D levels was significantly associated with Improvement in depression score