The Role of Vitamin D in PCOS

This episode explores the evidence on vitamin D and its role in the pathophysiology and clinical management of polycystic ovary syndrome (PCOS), with a focus on metabolic and reproductive outcomes. We break down proposed biological mechanisms, key findings from recent trials and reviews, and practical considerations for screening and supplementation in clinical practice. Designed for dietitians and women’s health professionals, this episode supports evidence-informed decision making when caring for individuals with PCOS.

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References:

1. Vitamin D and Polycystic Ovary Syndrome (PCOS): A Narrative Review (2025): [Akhter, D.S., Hannan, D.K., Chowdury, D.S., & Nasrin, D.S. (2025). Vitamin D and Polycystic Ovary Syndrome (PCOS): A Narrative Review. Scholars Journal of Applied Medical Sciences.]
2. Effects of vitamin D supplementation on metabolic parameters in women with polycystic ovary syndrome: a randomized controlled trial (2024): [Wen, X., Wang, L., Li, F., & Yu, X. (2024). Effects of vitamin D supplementation on metabolic parameters in women with polycystic ovary syndrome: A randomized controlled trial. Journal of Ovarian Research, 17(1). https://doi.org/10.1186/s13048-024-01473-6
3. Effects of vitamin D supplementation on metabolic parameters in women with polycystic ovary syndrome: a randomized controlled trial (2024)(2025): [Tóth, B. E., Takács, I., Valkusz, Z., Jakab, A., Fülöp, Z., Kádár, K., Putz, Z., Kósa, J. P., & Lakatos, P. (2025). Effects of vitamin D3 treatment on polycystic ovary symptoms: A prospective double-blind two-phase randomized controlled clinical trial. Nutrients, 17(7), 1246. https://doi.org/10.3390/nu17071246]
4. The impact of vitamin D supplementation on glycemic control and lipid metabolism in polycystic ovary syndrome: a systematic review of randomized control trials: [Yu, M., Chen, S., Liu, X., Dong, H., & Wang, D.-C. (2025). The impact of vitamin D supplementation on glycemic control and lipid metabolism in polycystic ovary syndrome: A systematic review of randomized controlled trials. BMC Endocrine Disorders, 25(1). https://doi.org/10.1186/s12902-025-01920-5]
5. Effect of vitamin D supplementation on lipid profile, and hormonal function in polycystic ovary syndrome: An umbrella systematic review and meta-analysis (2024): Tony Yin et.al.,: [Yin, T., Lin, W., Ming, K., Lv, H., Wang, Y., Yuanchao, L., Zhen, H., Yuan, J., & Asadi, H. (2024). Effect of vitamin D supplementation on lipid profile, and hormonal functions in polycystic ovary syndrome: An umbrella systematic review and meta-analysis. Prostaglandins & Other Lipid Mediators, 175, 106913. https://doi.org/10.1016/j.prostaglandins.2024.106913]

Transcript

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Hi, and welcome to the Femme Health Nutrition Podcast. I'm Nilu Demi, a registered dietician and founder of the Women's Health Nutrition Learning Hub, a platform where dieticians and nutrition professionals can learn about all things related to female health and nutrition. If you haven't already, you can check out the website at w hn learning hub.com. On the website, you can find many blog posts on women's health related topics, as well as some free resources you can download. You can also join my newsletter where I send biweekly research updates on a range of topics, as well as share new courses and learning opportunities as they become available. I do have a very interesting webinar coming up on November 20th with an incredible nutrition scientist, The topic is the role of micronutrients in premenstrual disorders, we'll be diving deep into the research of how things like Vitamin D and calcium and other micronutrients can impact Premenstrual disorders such as Premenstrual dysphoric disorder or PMDD. It's going to be super interesting If you would like to register, the link will be in the show notes. You can also find it on my website, and even if you're not able to attend live, we will be giving you access to the recording after the session. and if you're listening to this after November 20th. And you still want to watch the webinar, you can access it on the webinar library on w hn learning hub.com. So all of these links will be in the show notes. Now, if you're new to the podcast, I wanted to welcome you and just say that I'm so glad you're here and joining us on this journey of learning. If you've been here for a while and you've been listening, thank you so much for your continued support and commitment to the podcast and to learning about women's health, And whether you're a new listener or have been tuning in for a while, I would really appreciate it if you could either subscribe, leave a rating, or just share it with others. With podcasts, we don't get that direct feedback from listeners, so any sort of signal from you that tells me that this work is resonating will encourage me to keep going and to keep recording these episodes. Now before we dive into the content for today's episode, just a reminder that this podcast is intended as an educational podcast for dieticians, healthcare professionals, and really anyone interested in women's health and nutrition. The content is not intended as medical advice, and if you have any questions or concerns about your health, please consult with your healthcare team. So today we're going to be talking about the role of vitamin D in polycystic ovarian syndrome or PCOS, and I just wanted to thank my student, Tamara, for helping me put together the script for this podcast. She has done a fantastic job. So what we're going to do as usual, is we'll kind of examine some of the claims. We'll get into biological mechanisms, and then we'll look into the research to see what actual studies tend to show, and at the end we'll talk about how we can apply this learning to our practice. So as many of you may already know, PCOS is the most common endocrine disorder in women of reproductive age worldwide. So it's estimated that approximately six to 10% of women and individuals assigned female at birth of reproductive age worldwide have PCOS. PCOS is characterized by three central features, two of which are needed to make a diagnosis. So the first is ovulatory dysfunction, which often presents as irregular menstrual periods. Then we have hyperandrogenism. This can be seen either through lab work or it could be seen clinically through symptoms like acne, hair loss, and herm, which is excessive hair growth in areas of the body where typically females wouldn't see that. Pattern of hair growth, for example, on the chin, on the stomach, on the chest. And the third is polycystic ovarian morphology. And this is where you see little immature follicles on the ovary, on ultrasound. So two of the above three are needed to make a diagnosis for PCOS, and this is referred to as the Rotterdam criteria. Underlying these is a common thread, and that is insulin resistance, which is seen in at least 75% of women with PCOS, regardless of their body size. And there's also a state of chronic low grade inflammation that could also disrupt metabolic and hormone balance. Now when it comes to vitamin D, what's really interesting is how vitamin D deficiency appears to be disproportionately common among those who have PCOS. So there are studies that estimate around 67 to 85% of those who have PCOS have suboptimal vitamin D levels. Of course, we've known for a long time that Vitamin D is essential for calcium metabolism and bone health. Over the past decade or more, we are learning that vitamin D also plays a role in metabolic health, specifically in insulin secretion, lipid metabolism, inflammation, and even hormone production. All of these, which are important in PCOS pathophysiology. now when we look at the potential mechanisms, vitamin D can act as a hormone, and once it's converted to its active form, it can bind to vitamin D receptors, which are present in multiple tissues that are relevant to PCOS. So, for example, the pancreatic beta cells, and this is where it may help regulate insulin secretion in the liver and adipose tissue where it can influence lipid metabolism and inflammation. Vitamin D may also act on ovarian tissue, specifically on granulosa and theca cells in the ovaries where it can impact hormone synthesis. So putting this all together mechanistically, we can kind of group Vitamin D's effect into three broad areas. So the first is insulin regulation. So vitamin D may enhance insulin sensitivity by increasing insulin receptor expression and target tissues. When there are more receptors, that means an individual becomes more sensitive to insulin. It may also suppress pro-inflammatory cytokines, which can impair insulin action. Vitamin D may also act on the liver to reduce lipid synthesis. And also can enhance lipid clearance. as a result, some studies will show that when there is adequate vitamin D, This can help lower triglycerides total cholesterol, and LDL cholesterol. Now, vitamin D, as you mentioned, can have reproductive and hormonal effects as well. So in ovarian cells, vitamin D promotes aromatase activity, and aromatase is an enzyme that converts androgens to estrogens, and this helps improve follicular development. Vitamin D may also help increase something called the sex hormone binding globulin, or SHBG. And when there's more of this SHBG, it will bind to free testosterone. And when free testosterone is bound, it's less likely to act on tissues and lead to those symptoms of hyperandrogenism. when we look at all these potential mechanisms, the biology makes sense, but as we know, sometimes mechanism doesn't actually translate into clinical outcomes. So let's review what the research actually shows. there was a narrative review that synthesized findings from observational studies and interventional studies, and this was done in 2025, and this group of researchers found that Vitamin D deficiency is highly prevalent in PCOS. So it just confirmed previous findings, they also found that lower vitamin D levels correlate with more insulin resistance, higher fasting insulin, and lower sex hormone binding globulin. When they looked at the results of small intervention trials, they found that vitamin D either on its own or combined with metformin. Tended to improve insulin sensitivity, menstrual regularity, and even pregnancy rates. However, they found that the effects on androgens were inconsistent and BMI and Anthropometric remained largely unaffected. Now there are also a couple of randomized control trials that I will highlight. There was a randomized control trial of 60 women who had PCOS and Vitamin D deficiency, and they were randomized to receive either 2000 units per day of vitamin D or to just receive lifestyle counseling alone for 12 weeks without any supplementation by the end of the trial, the group that received the supplementation had significantly decreased fasting insulin and insulin resistance levels. Their lipid parameters had improved, so triglycerides, total cholesterol and LDL were all significantly lower. But HDL cholesterol didn't change. The authors noted that the improvements were actually most pronounced in those who had obesity or existing insulin resistance. Now there was another prospective, double-blinded, randomized control trial that focused on reproductive outcomes with vitamin D supplementation. So this was a study with 84 participants. Half of them were randomized to receive 30,000 units of vitamin D per week for 24 weeks, and half of them received a placebo. They found that in those who received the vitamin D, their cycle length decreased significantly by about 11 to 31 days. Their ovulation rates increased, so at baseline it was around 40%, and then after vitamin D supplementation, it increased 59 to 65%. In those who had hyperandrogenism, they found that testosterone dropped significantly and sex hormone binding globulin increased. and 20% of them saw improvements on their ultrasound after 12 weeks. So these are really clinically meaningful changes from a reproductive perspective, especially in those who are struggling with anovulation. Now, kind of zooming out from individual trials there were two systematic reviews and meta-analysis that were done, and these actually looked at metabolic outcomes versus reproductive. but these studies also confirm that vitamin D supplementation does have benefits. So they found with vitamin D supplementation and those who are deficient, there's improved fasting glucose. insulin triglyceride, total cholesterol and LDL levels, But no change in HDL levels. It would be good for us to see these systematic reviews done on reproductive outcomes as well. Overall, looking at the whole body of the research, the consensus across these studies is that vitamin D supplementation when there's deficiency, may improve lipid profiles and sometimes improve insulin sensitivity, and it may also improve ovulation and cycle regularity, but we need a little bit more research on that as well. Now, of course, the research isn't perfect, and of course there are several limitations here. So across studies, sample sizes are small and durations are short. So often around eight weeks to 12 weeks, sometimes up to 24 weeks. There is a lot of variability in the doses. So we see anywhere from 2000 per day to 50,000 per week. So we don't really know what the optimal dose of supplementation is. Many of the trials don't necessarily control for things like sunlight exposure, dietary intake, seasonal effects. So that needs to be considered. And they don't have a lot of research on the impacts of vitamin D on sex hormones specifically. Now if you're a healthcare professional and dietician and you're thinking, what can you take away from this? The first is if you're able to, to screen for deficiency. I know that's not possible in all cities or in all provinces, depending on where you are. If you are able to check for vitamin D levels, that would be fantastic'cause they can also guide the dose that's recommended to the patient. The goal is never mega doses, We really want to either correct or prevent a deficiency, so you can really use your clinical judgment and you may also want to collaborate with the individual's physician If you feel like higher doses may be warranted temporarily, and of course vitamin D is a part of the bigger picture, you still want to be focusing on things like macronutrient, intake, Omega-3 rich foods, regular movement alongside the supplementation. So just setting those realistic expectations that vitamin D on its own obviously is not going to solve everything. That brings us to the end of today's episode. Thank you so much for tuning in. If you've enjoyed this content, please consider following the podcast or leaving a rating. And if you have any feedback or suggestions for future episodes, feel free to email me at hello at w hn learning hub.com. I'll include that in the show notes as well. And you can also find the references, the link to register for the webinar as well as the link to the website in the show notes as well. So thank you again for tuning in and I hope you have a lovely day. Thank you.