Here are some studies about the effects of vitamin D for acne treatment:
Conclusion: This study involving 35 acne patients found that a month of taking 2,500 – 5,000 IU of supplemental vitamin D daily produced improvement in 100% of the subjects and almost completely cured it in 90%. Within ten days of stopping the treatment, 10% of subjects reported a return of their acne. Also see Vitamin D in the Treatment of Acne (1940)
Conclusion: In 204 controlled cases, Dermatologist Merlin Maynard found daily supplementation of 5,000 – 14,000 IU of vitamin D2 to be more effective for the treatment of acne than x-ray treatment, the previously most successful treatment for acne at the time. In addition to being the most effective acne treatment, Maynard also discovered that vitamin D had the positive side effects in patients of increasing healthy weight, reducing fatigue, improving overall feelings of well-being, and healing other skin diseases such as psoriasis. In comparison to the other acne treatments at the time, vitamin D is also much more affordable. Medical doctors George V. Kulchar and Henry J. Templeton also write of similar success using vitamin D supplementation and sun/UV light exposure for treating acne patients.
Conclusion: The vitamin D levels of 43 acne patients and 46 healthy control subjects were measured. The acne group had “significantly lower” vitamin D levels than the control group.