Here are some studies about vitamin D, bright light, and seasonal affective disorder:

Effect of Sunlight and Season on Serotonin Turnover in the Brain (2002)

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.


Vitamin D Enhances Mood in Healthy Subjects During Winter (1998)

Conclusion: This random double-blind placebo-controlled trial found vitamin D3 supplementation to be significantly effective for alleviating depression from seasonal affective disorder.


Bright Light Treatment of Winter Depression: A Placebo-Controlled Trial (1998)

Conclusion: In a randomized control trial experiment involving 96 seasonal affective disorder patients, three weeks of bright light therapy proved to have an antidepressant effect on winter depression sufferers. (You know… like SUNLIGHT)


Vitamin D vs Broad Spectrum Phototherapy in the Treatment of Seasonal Affective Disorder (1999)

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?


Morning vs Evening Light Treatment of Patients with Winter Depression (1998)

Conclusion: Morning bright light therapy is more effective as an antidepressant compared to evening bright light therapy. (Yep, the sun rises in the morning.)


Natural Light Treatment of Seasonal Affective Disorder (1996)

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.


Prevalence of Seasonal Affective Disorder at Four Latitudes (1990)

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.




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