By Amy Medling, founder of PCOS Diva
Updated: December 2021
Vitamin D plays a critical role in our body’s everyday functions. It promotes bone growth, calcium absorption, reproduction, and general immunity against common illnesses among other things. While the best way to get vitamin D is by sunlight exposure, most of us require additional supplementation, especially in winter months or if always protected by sunscreen.
Studies show that three out of four women with PCOS have a vitamin D deficiency  and that, “…vitamin D deficiency is associated with multiple risk factors in PCOS women.” There are proven correlations between vitamin D deficiency and insulin resistance and inflammation as well as many other serious illnesses. Vitamin D (particularly when paired with vitamin K1 and K2) is effective in reducing many symptoms of PCOS, supporting a healthy immune system, promoting bone and artery health, and supporting reproductive health by promoting healthy estrogen levels.
Possibly most interesting to women with PCOS, a recent study has investigated the effects of vitamin D supplementation on infertility in women with PCOS and insulin resistance. The study concluded that vitamin D supplementation is correlated with improved embryo quality and a higher pregnancy rate.
Vitamin D and why your body needs it
Vitamin D is best known as the sunshine vitamin because exposing your skin to sunlight is the best way to get it.
Other healthy sources include fatty fish such as salmon, mackerel, and sardines, and eggs as well as some plant sources like mushrooms. For those who are deficient or unable to adequately absorb vitamin D from natural sources, supplementation is an option. Everyone should know their level of this critical nutrient.
Studies have shown supplemental vitamin D is linked to a wide range of benefits including increased brain power, stronger immune system, bone health, and overall well-being.
Supplementation has also been linked to reduced risks of heart disease, cancers, multiple sclerosis, and even diabetes. [1, 2] For men, a higher vitamin D level is linked to increased sperm production which can help with infertility. 
Vitamin D, PCOS, and in-vitro fertilization
For some, maintaining adequate levels of vitamin D may be the key to improving fertility. This has been proven in a study done on in-vitro fertilization PCOS patients with insulin resistance.
The study published in January of 2019 included 305 infertile PCOS patients undergoing in-vitro fertilization. The results were conclusive: women who had optimal levels of vitamin D at the time of in-vitro fertilization had a higher chance of clinical pregnancy than those who had lower vitamin D levels. 
The researchers explained vitamin D supplementation helped improve embryo quality which automatically lead to a significantly higher pregnancy rate.
While this is the most recent study done on vitamin D and pregnancy, this isn’t the first. As far back as 2010, scientists have linked vitamin D supplementation to higher chances of pregnancy following in-vitro fertilization. 
In addition to vitamin D, inositol was found to have promising effects on reproductive health. A study in October 2018 tested the effect of myo-inositol supplementation. The study was driven by the fact that women with PCOS and insulin resistance are often deficient in inositol, a substance that supports hormone regulation including insulin, thyroid-stimulating hormone (TSH), and follicle-stimulating hormone (FSH).  Women with PCOS and insulin resistance often have problems metabolizing inositol which leads to low levels of the above-mentioned. The study found that myo-inositol supplementation was able to help the body maintain critical hormone levels and improve oocyte and embryo quality.
Vitamin D and insulin resistance
Studies have shown that most women with PCOS have insufficient vitamin D levels, and vitamin D replacement therapy may have a beneficial effect on insulin resistance in obese women with PCOS.  People with higher levels of this vitamin are 40% less likely to develop diabetes. The vitamin helps the pancreas secrete insulin. It also reduces systemic inflammation, which influences insulin resistance. 
Who should supplement with vitamin D?
Supplementation is meant to support vitamin and mineral stores and not as your primary source of nutrients. However, if you’re prone to a deficiency or your blood test shows low vitamin D levels, supplementation may help.
When searching for the right vitamin D supplement, be sure to look for one that is third-party certified to ensure you’re getting what you pay for. Also, look for one that includes vitamin k for optimal absorption.
Amy Medling, best-selling author of Healing PCOS and certified health coach, specializes in working with women with Polycystic Ovary Syndrome (PCOS), who are frustrated and have lost all hope when the only solution their doctors offer is to lose weight, take a pill, and live with their symptoms. In response, Amy founded PCOS Diva and developed a proven protocol of supplements, diet, and lifestyle programs that offer women tools to help gain control of their PCOS and regain their fertility, femininity, health, and happiness.
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- Zhao J, Liu S, Wang Y, et al. Vitamin D improves the outcome of in vitro fertilization (IVF) in infertile women with polycystic ovary syndrome and insulin resistance. Minerva Med. 2019;
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- Laganà AS, Vitagliano A, Noventa M, Ambrosini G, D’anna R. Myo-inositol supplementation reduces the amount of gonadotropins and length of ovarian stimulation in women undergoing IVF: a systematic review and meta-analysis of randomized controlled trials. Arch Gynecol Obstet. 2018;298(4):675-684.
- J Endocrinol Invest. 2010 Apr;33(4):234-8. Epub 2009 Oct 9.The effect of vitamin D replacement therapy on insulin resistance and androgen levels in women with polycystic ovary syndrome.
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