Here are some studies about vitamin D, bright light, and seasonal affective disorder:
Conclusion: A study of 101 healthy men found that their serotonin levels were lowest during winter, when there’s less sunlight, but “rose rapidly” as the amount of bright sunlight increased.
Conclusion: This study found that subjects who underwent a UVA irradiation session twice a week for three weeks tested as having higher serotonin levels and lower melatonin levels compared to a control group. The UVA-irradiated group also reported feeling “significantly more balanced, less nervous, more strengthened, and more satisfied with their appearance.” So although you can’t get vitamin D from UVA, this study demonstrates that there are still health benefits of UVA exposure and bright light and that it’s not a bad idea to enjoy a balance of full-spectrum sunlight.
Canadian Consensus Guidelines for the Treatment of Seasonal Affective Disorder: A Summary of the Report of the Canadian Consensus Group on SAD (1999)
Note: 162-page ridiculously detailed and comprehensive guide on seasonal affective disorder.
Conclusion: This random double-blind placebo-controlled trial found vitamin D3 supplementation to be significantly effective for alleviating depression from seasonal affective disorder.
Conclusion: Bright light therapy (you know… like sunlight) was found to be an effective antidepressant compared to placebo light in this randomized control trial of 96 seasonal affective disorder patients. However, this effect was not achieved until after three weeks of treatment.
Conclusion: In this particular randomized control trial, high-dose vitamin D therapy proved to be an effective treatment for alleviating depressive symptoms of seasonal affective disorder. Could winter vitamin D-deficiency resulting from reduced UVB solar radiation be playing a role in seasonal affective disorder?
Conclusion: Morning bright light therapy is more effective as an antidepressant compared to evening bright light therapy. (Yep, the sun rises in the morning.)
Conclusion: This double-blind study compared the effects after 1 week of a daily 1-hour morning walk outdoors versus a daily half-hour placebo light treatment (only 2800 lux) in seasonal affective disorder patients. The morning walk proved to be effective for regulating melatonin secretion and reducing cortisol, whereas the placebo light treatment did neither.
Conclusion: A “Seasonal Pattern Assessment Questionnaire” involving questions about experience with winter seasonal affective disorder was mailed to people at four different areas of latitude in the U.S.: New Hampshire, New York, Maryland, and Florida. Rates of winter depression were “significantly higher” in the more northern latitudes and this correlation “applied predominantly to the age groups over 35.” The more northern latitudes would be the areas that receive less sunlight.
Seasonal Affective-Disorder – A Description of the Syndrome and Preliminary Findings with Light Therapy (1984)
Conclusion: This is a study from world-renowned seasonal affective disorder expert Norman Rosenthal. Bright light therapy vs placebo lighting was tested on a group of seasonal affective disorder patients. The bright light therapy was found to be effective for reducing symptoms of seasonal affective disorder. Other findings are that those suffering from SAD typically report to crave bright light, sunbathing, and trips to beach locations. Many also report a complete disappearance of their symptoms within days of arriving in Florida or the Caribbean. Symptoms also typically disappear with the coming of Spring and Summer. Is seasonal affective disorder actually just sunshine deficiency?