take home points
Vitamin D supplementation improved menstrual cycle regularity. However, in one study, these effects were not large enough to result in normal-length cycles, and in the other study, in is unclear how cycle regularity categories were defined. This intervention alone likely does not solve all menstrual cycle problems associated with PCOS.
There is some evidence that supplementation leads to small improvements in insulin resistance and metabolic health.
Some, but not all, studies find positive effects of supplementation on triglyceride and cholesterol levels.
All studies excluded participants with adequate levels of vitamin D. Given the relatively small and inconsistent effects found for those who were deficient, I suspect those who are not deficient will not experience benefits.
Studies all used supplementation that was at most once a week, unlike most supplements that encourage daily consumption.
You can consume too much vitamin D! Blood testing is recommended prior to supplementation and should ideally be repeated to ensure your vitamin D levels do not get too high.
References
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Ardabili HR, Pourghassem Gargari B, and Farzadi L. 2013. Effects of vitamin D on cardiovascular disease risk factors in polycystic ovary syndrome women with vitamin D deficiency. Journal of Endocrinological Investigation, 36(1):28-32. doi: 10.3275/8303.
Davis EM, Peck JD, Hansen KR, Neas BR, and Craig LB. 2019. Associations between vitamin D levels and polycystic ovary syndrome (PCOS) phenotypes. Minerva Endocrinology, 44(2): 176–184. doi:10.23736/S0391-1977.18.02824-9.
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Krul-Poel YHM, Koenders PP, Steegers-Theunissen RP, ten Boekel E, ter Wee MM, Louwers Y, Lips P, Laven JSE, Simsek S. 2018. Vitamin D and metabolic disturbances in polycystic ovary syndrome (PCOS): A cross- sectional study. PLoS ONE, 12:e0204748. https://doi.org/10.1371/journal. pone.0204748
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National Institutes of Health. 2023. Vitamin D: Fact Sheet for Health Professionals. Available: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Accessed January 9, 2023.
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Trummer C, Schwetz V, Kollmann M, Wölfler M, Münzker J, Pieber TR, Pilz S, Heijboer AC, Obermayer‐Pietsch B, and Lerchbaum E. 2019. Effects of vitamin D supplementation on metabolic and endocrine parameters in PCOS: a randomized-controlled trial. European Journal of Nutrition 58:2019–2028. https://doi.org/10.1007/s00394-018-1760-8.
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