Vitamin D supplementation has recently become all the rage. Many popular podcasts advertise a promo for Athletic Greens that provides a free year’s supply of Vitamin D. Their supplement contains 1000 IU of Vitamin D, while the recommended daily allowance for Vitamin D is 600 IU for adults aged 19 - 70.

Do you actually need a year’s supply of 1000 IU of Vitamin D? Let’s see what the literature says!

what is vitamin D?

Vitamin D is a rare vitamin that our bodies can actually make! When our skin is exposed to UVB radiation from the sun, a form of cholesterol in the skin gets converted to previtamin D3, which eventually gets converted into the active form of vitamin D3 that our bodies use through processes in the kidney and liver (NIH 2023).

However, there is substantial variation in just how much vitamin D gets produced from any given bout of sun exposure. Time of day, season, cloud cover, smog, skin color, and sunscreen use all affect the amount of UVB radiation that actually hits and penetrates the skin. And then on top of that, humans vary tremendously in their abilities to produce vitamin D. People who are older tend to produce less vitamin D, and studies show that even among non-elderly adults, there is substantial variation in the blood levels of vitamin D resulting from the same level of sun exposure (Giustina et al. 2020). It is unclear why this variation occurs, but there is some evidence that it is the result of genetic variation.

Vitamin D is perhaps most commonly associated with bone health. It plays a major role in increasing the levels of calcium in the blood to be used in bone and teeth. People taking calcium supplements are often encouraged to supplement with vitamin D as well because vitamin D increases the absorption of calcium from the intestines.

Vitamin D also rose in popularity during the COVID-19 pandemic when some studies showed that vitamin D supplementation could reduce the severity of COVID infections (Shah et al. 2022). And indeed, vitamin D plays a role in stimulating immune system responses, and frequent colds can be a sign of vitamin D deficiency.

Other studies have linked increased levels of vitamin D with improved metabolic, cardiovascular, and reproductive health, which is how the supplement became a popular one for polycystic ovary syndrome (PCOS).

sunshine and vitamin d

In the right conditions, about 10 to 15 minutes of sunshine on your arms and legs a few times a week could generate enough vitamin D to meet your needs. However, if you live at even moderately high latitudes (north of 37 degrees N or south of 37 degrees S), only summer time will provide rays strong enough to stimulate much production of vitamin D. Not to mention that in these regions, people often don’t walk around with their arms and legs exposed all year long!

Food sources of vitamin D

While we often associate vitamin D with sunshine, some foods also provide vitamin D, and these foods may be especially important for people living farther from the equator.

The list below contains the best food sources, with vitamin D content listed in IU (international units). As a reminder, the RDA is 600 IU per day for adults. All data from USDA (2019).

1. Cod liver oil, 1 tbsp, 1360 IU

2. Rainbow trout, 1 oz., 215 IU

3. Salmon, 1 oz., 128 - 190 IU

4. Canned light tuna, 1 oz., 77 IU

5. Herring, 1 oz., 61 IU

6. Milk, 1/2 cup, 59 IU

7. Yogurt, 4 oz., 58 IU

8. Mushrooms, 1/2 cup, 57 - 555 (mushrooms exposed to sunlight synthesize vitamin D!)

9. Canned sardines, 1 oz., 55 IU

10. Eggs, 1 egg, 50 IU

11. Fortified orange juice, 1/2 cup, 50 IU

12. Tilapia, 1 oz., 42 IU

13. Flounder, 1 oz., 39

To help my members get adequate vitamin D, I include salmon and eggs regularly in my meal plans and often include canned tuna. If you struggle to incorporate these foods in your diet, consider signing up for my meal plans. Your first month is free!

Vitamin D and polycystic ovary syndrome: Is there a relationship between Vitamin D levels and PCOS?

Early research on the subject of vitamin D and PCOS looked for correlations between blood levels of vitamin D and the likelihood that someone had PCOS. The literature finds that, on average, females with PCOS tend to have lower levels of serum vitamin D, although not every study finds this difference to be statistically significant, likely due to substantial variation across individuals (Davis et al. 2019, Krul-Poel et al. 2018, Li et al. 2011).

One study splits its sample into lean vs. overweight females. Among lean females, there is no difference in average vitamin D levels in females with or without PCOS, while among overweight women, those with PCOS had vitamin D levels that were about 33% lower than those without PCOS (Joham et al. 2016). This difference may explain some of the variation in findings that do not separate participants by body weight category.

While correlations suggest that there may be a relationship between vitamin D levels and PCOS, they cannot tell us conclusively if low vitamin D levels contribute to PCOS or if PCOS leads to low vitamin D levels. Nor does it tell us conclusively that vitamin D supplementation is necessarily helpful for PCOS.

So let’s discuss that literature next!

does supplementation with vitamin D help with pcos?

There are a lot of studies that have used randomized control trials (our gold standard for researching interventions) to determine whether vitamin D supplementation improves various markers of health for females with PCOS.

I have chosen to highlight four studies below based on the following criteria: 1) the study was published in a reputable journal (there are a lot of open access journals out there where you basically pay to get it published without it going through a legitimate peer-review process), 2) the paper was accessible to me without a paywall (most were, thankfully!), 3) the study considers markers prominent markers of health (a few studied fairly obscure markers that don’t tell us much about the key concerns for females with PCOS).

Vitamin D and Menstrual Cycle Regularity

I am going to start with two studies that included menstrual cycle length in addition to other markers because I think this is an especially important marker of health for females with PCOS. It’s our 6th vital sign!

The first of these studies (Irani et al. 2015) recruited 68 females with PCOS who were also deficient in vitamin D.

Of these participants, 45 were randomly assigned to supplement with vitamin D and consumed:

• One capsule of 50,000 IU of vitamin D each week.

23 were randomly assigned to the control group, and they consumed:

• One capsule filled with lactose monohydrate powder, which looked similar to the vitamin D capsule.

Both groups consumed their respective capsules weekly for 8 weeks.

The table below summarizes the results after 8 weeks of supplementation. As expected, the group consuming the placebo experienced no changes in any marker of health.

The group supplementing with vitamin D experienced an almost 34% reduction in menstrual cycle length, which is pretty significant. However, it should be noted that the average cycle length after treatment was 60 days, which is still considered to be longer than “normal” (23 - 35 days).

They also experienced a 21% decrease in Ferriman-Gallway score, which is a marker of hirsutism (masculine patterns of facial and/or body hair). Interestingly, despite these changes in cycle length and overt symptoms of excess androgen hormones, no changes in any reproductive hormones occurred.

While most markers of cardiovascular health remained unchanged with supplementation, the treatment group did experience an 18% decrease in triglyceride levels, which indicates a lower risk for cardiovascular disease.

While the intervention in the paper above only included vitamin D supplementation, Jafari-Sfidvajani et al. (2018), considered vitamin D supplementation among females with PCOS who were also following a calorie-restricted diet.

This study recruited 60 females with PCOS who had BMIs of 25 or higher (overweight or obese) and who had deficient serum vitamin D levels.

Thirty of the participants were randomly assigned to the treatment group, and they consumed:

• One capsule of 50,000 IU of vitamin D each week.

Thirty of the participants were randomly assigned to the control group, and they consumed:

• One capsule filled with paraffin oil, which looked similar to the vitamin D capsule.

Both groups followed a diet consisting of:

• 500 calorie deficit relative to their estimated caloric needs

• 55% of their calories from carbohydrates

• 15% of calories from protein

• 30% of calories from fat

The intervention lasted for 12 weeks. The table below contains the percent change for various markers of health after the 12-week intervention.

Both groups experienced similar decreases in body weight, BMI, waist circumference, waist-to-hip ratio, and fat mass. Neither group experienced any improvements in reproductive hormone levels, and the control group even experienced an increase in DHEA, an androgen hormone which can be elevated in females with PCOS.

As expected, the group supplementing with vitamin D saw an increase in their serum vitamin D levels, while those taking the placebo did not.

Like the previous study, this one recorded effects on menstrual cycle regularity. It is unclear exactly how they defined “regularity.” Menstrual cycles between 23 and 35 days are generally considered “regular” or “normal” and I am assuming that was their definition. Similarly, their definition of oligomenorrhea is unclear. It usually means fewer than 6 to 8 cycles per year. Given that their intervention lasted only 12 weeks, they must have used a different metric, but they do not state what. Amenorrhea is the absence of any period, which is fairly straightforward.

Given the lack of clarity on regularity, I think these results should be interpreted with caution.

While both groups experienced increases in likelihood of having a regular period and decreases in likelihood of having either oligomenorrhea or amenorrhea, a larger portion of participants in the group supplementing with vitamin D experienced improvements in cycle regularity.

Vitamin D & Cardiovascular and Metabolic Health

The next two studies ignored menstrual cycle regularity and instead chose to focus on only metabolic and cardiovascular health.

The earlier of these studies was done by Ardabili et al. (2012 and 2013). This study recruited 60 females with PCOS who were deficient in vitamin D.

Half of the participants were randomly assigned to the treatment group, and consumed:

• One capsule containing 50,000 IU of vitamin D every 20 days.

The other half was assigned to the control group, and consumed:

• One capsule containing paraffin oil every 20 days.

The study lasted for two months. The table below shows the changes in various health markers after the two-month intervention. As expected, the placebo group experienced no changes during the intervention period.

Similarly, as we’d expect, the treatment group experienced an increase in serum vitamin D levels. They also experienced a decrease in parathyroid hormone, a hormone that gets released when your body detects low calcium levels. Increasing vitamin D increases absorption and retention of calcium, so less parathyroid hormone gets released. This is a positive shift because elevated parathyroid hormone means your body is pulling calcium from your bones to keep blood calcium levels in the optimal range.

The treatment group also experienced reductions in total cholesterol and triglycerides. This study is one of the few studies that not only tests for HDL and LDL cholesterol (commonly thought of as good and bad cholesterol, respectively), but also VLDL cholesterol. VLDL cholesterol is a subset of LDL cholesterol, and there is increasing evidence that we actually care about VLDL levels in terms of artery health and heart attack risk. Importantly, this study found a 20% reduction in VLDL levels among those who supplemented with vitamin D.

While they tested for a variety of measures of metabolic health, the treatment group only experienced a significant improvement in one of those measures, suggesting a weak effect on metabolic health. Had the study continued for longer, perhaps we would see changes in other measures of metabolic health, but we can’t say for sure.

The last study I will discuss here was conducted by Trummer et al. (2019). They recruited 180 females with PCOS who were also deficient in vitamin D.

Two-thirds of their participants were randomly assigned to the treatment group, and they consumed:

• 50 oily drops that contained a total of 20,000 IU weekly

One-third of their participants were assigned to the control group, and they consumed:

• 50 oily drops of placebo weekly

Both groups consumed their respective drops for 24 weeks. The table below shows the effects of the 24-week intervention. As we saw with previous studies, no changes were observed for the group taking the placebo.

The group supplementing with vitamin D saw increases in two forms of serum vitamin D levels. The first is the form of vitamin D tests usually capture. This form is one step away from the active form that our bodies actually use. This form tends to persist in the body for a longer period of time and tells us more about long term vitamin D status. The active form does not persist very long and can be influenced by recent consumption of vitamin D or sun exposure.

As expected, parathyroid hormone also decreased among the vitamin D group. As discussed above, parathyroid hormone is released when blood calcium levels get too low, and it stimulates the release of calcium from bones.

This study used 7 measures of insulin resistance, and only one indicated an improvement in insulin resistance. This test, a 60-minute oral glucose tolerance test, measures blood sugar levels 60-minutes after consumption of 75 g of glucose. A lower score indicates better insulin sensitivity and better blood sugar management. However, the fact that none of the other metrics improved suggests that affects on insulin resistance are marginal at best.

Lastly, it’s important to note that this study did not find any effects on measures of cardiovascular health, unlike previous studies. This could be a result of the lower dose used in this study, but without further investigation, we cannot know for sure.

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

Ardabilia HR, Gargarib BP, and Farzadic L. 2012b. Vitamin D supplementation has no effect on insulin resistance assessment in women with polycystic ovary syndrome and vitamin D deficiency. Nutrition Research, 32:195–201. doi:10.1016/j.nutres.2012.02.001

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.

Giustina A, Bouillon R, Binkley N, Sempos C, Adler RA, Bollerslev J, Dawson-Hughes B, Ebeling PR, Feldman D, Heijboer A, Jones G, Kovacs CS, Lazaretti-Castro M, Lips P, Marcocci C, Minisola S, Napoli N, Rizzoli R, Scragg R, White JH, Formenti AM, Bilezikian JP. 2020. Controversies in Vitamin D: A Statement From the Third International Conference. JBMR Plus. 4(12):e10417. doi: 10.1002/jbm4.10417.

Irani M, Seifer DB, Grazi RV, Julka N, Bhatt D, Kalgi B, Irani S, Tal O, Lambert-Messerlian G, and Tal R. 2015. Vitamin D Supplementation Decreases TGF-􏰆1 Bioavailability in PCOS: A Randomized Placebo- Controlled Trial. The Journal of Clinical Endocrinology & Metabolism, 100(11):4307– 4314. doi: 10.1210/jc.2015-2580.

Jafari‐Sfidvajani S, Ahangari R, Hozoori M, Mozaffari‐Khosravi H, Fallahzadeh H, and Nadjarzadeh A. The effect of vitamin D supplementation in combination with low‐calorie diet on anthropometric indices and androgen hormones in women with polycystic ovary syndrome: A double‐blind, randomized, placebo‐controlled trial. Journal of Endocrinological Investigation, 41:597–607 https://doi.org/10.1007/s40618-017-0785-9

Joham AE, Teede HJ, Cassar S, Stepto NK, Strauss BJ, Harrison CL, Boyle J and de Courten B. 2019. Vitamin D in polycystic ovary syndrome: Relationship to obesity and insulin resistance. Molecular Nutrition & Food Research. 60:110–118. https://doi.org/10.1002/mnfr.201500259

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

Li HWR, Breretona RE, Anderson RA, Wallace A, and Ho CKM. 2011. Vitamin D deficiency is common and associated with metabolic risk factors in patients with polycystic ovary syndrome. Metabolism Clinical and Experimental 60:1475-1481.

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.

Shah K, Varna VP, Sharma U, Mavalankar D. 2022. Does vitamin D supplementation reduce COVID-19 severity? A systematic review. QJM. 115(10):665-672. doi: 10.1093/qjmed/hcac040.

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.

U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. fdc.nal.usda.gov.

Disclaimer: This post is not intended to diagnose or treat any medical issues. It is intended for informational purposes only. I am not a medical practitioner. Always consult a trusted healthcare provider with any questions you may have about a medical condition or treatment and before starting any new health care regimen.