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The PCOS Newsletter is a weekly publication answering one PCOS question at the time so we can be empowered by knowledge.

An issue will land in your inbox each Sunday

PCOS and Vitamin D

This week’s question

Should I take Vitamin D for my PCOS?

In today’s newsletter, we cover the following:

  • Should I supplement with Vitamin D?

  • What is the link between Vitamin D and PCOS?

  • Why is Vitamin D so important to our health?

  • Why are so many people deficient in Vitamin D?

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I would like to start today’s newsletter with a simple question: When did you last test your Vitamin D levels?

Vitamin D has receptors that modulate the expression of 229 genes in more than 30 different tissues, such as the skeleton, brain, breast, pancreas, parathyroid glands, immune cells, and ovaries. Well, now imagine being deficient in it. How is your body going to react?

When it comes to PCOS, there is so much discussion about the symptoms; insulin resistance, weight gain, acne etc., but we forget that our body runs on critical nutrients such as Vitamin D. The above symptoms of PCOS result from certain processes not working well. Understanding these processes and how nutrients interact with them is the key to unlocking the management of PCOS.

What is the link to PCOS?

The research on this is pretty solid. We know that women with PCOS who are deficient in Vitamin D have higher androgens and insulin levels.

Numerous studies show that Vitamin D deficiency is linked to insulin resistance as well as impaired glucose and lipid metabolism (if you are curious on how insulin resistance leads to excess androgens, have a read here). It is thought that Vitamin D also has a direct role in egg development, although the exact mechanism is not fully understood yet. Vitamin D also plays a role in lowering inflammation. All of the above are directly linked to some of the hallmark symptoms of PCOS.

Why is Vitamin D so key to our health?

Vitamin D is produced in our skin as a response to sunlight or ingested from our food. It then gets metabolised by the liver and kidneys to the form that is needed by our organs. Vitamin D activates its receptor (VDR) as it circulates through the blood.

Its role varies, but these are some of the most critical functions:

  1. Our reproductive system expresses VDR in the ovaries, the placenta and the fallopian tube. Vitamin D has been found to have an impact on fertility, but also the quality of pregnancy.

  2. Calcium and Phosphorus absorption - Vitamin D is able to increase the absorption of Calcium when ingested, stimulating bone mineralisation and the uptake of Calcium by our kidneys when needed. This mechanism is the reason why a deficiency can increase the risk of bone-related disease. This is also relevant for us with PCOS, as calcium and Vitamin D are involved in insulin secretion. In addition, Calcium is a critical nutrient in our muscle health.

  3. Immune system - Vitamin D’s effect on the immune system has vast research, including on auto-immune diseases. Vitamin D is thought to be able to modulate inflammation. This is relevant for us, as it’s known that women with PCOS have higher inflammation levels. Additionally, microbes slow down the reaction of our immune system by dysregulating the VDR to increase their chance of survival. If you are already deficient, it makes their job easier.

  4. Gene transcription - Activated VDR attaches itself to DNA and thus influences proteins from our genetic code. This is the primary mechanism by which scientists believe that deficiency in Vitamin D can be associated with autoimmune diseases, certain cancers, and dementia.

Should I be supplementing?

You should be supplementing with Vitamin D only if you are deficient. You can do a super simple at-home test and send your blood sample in if you are not able to get it through your GP. It’s pretty cheap and very efficient.

The ranges are as follows:

  • <25 nmol/L – Deficient

  • 25-50 nmol/L – Insufficient

  • 50-75 nmol/L – Adequate

  • >75 nmol/L – Optimum

Supplementation can help boost levels to healthy levels. The NHS in the United Kingdom recommends that everyone should consider taking a daily supplement containing 10 micrograms (400 UI) of vitamin D during the autumn and winter.

Besides that, the science gets a bit unclear regarding the direct effect of supplementation on different disease markers. Deficiency in this key vitamin has been associated with many diseases. However, when supplementing with it, results are not always consistent. Some studies show improvements in markers, whilst some don’t. This can suggest that vitamin D may be more an associative than a causal factor in acute and chronic disease. Despite this, it is also thought that poor study design can be linked to these results. Supplementing when you are not deficient in the first place might also influence some of the non-favourable results.

With that in mind, Vitamin D supplementation has not always been found to move some markers for women with PCOS. However, in another meta-analysis done in 2018, they found that the dosage, frequency and co-supplementation matter. A daily dose of less than 4000UI combined with a Calcium supplement showed improvements in insulin and androgen markers. It is known that insulin secretion is a calcium-dependent process; thus, vitamin D, involved in the absorption of calcium, may influence this process.


lease speak to a healthcare professional before starting any supplementation regime. Even though I am trained to recommend supplementation dosages, it’s essential you go through a consultation before taking anything. Supplements, like medication, need to be checked for interactions and reviewed as part of your overall health.

Why are so many people deficient?

Vitamin D deficiency became a public health problem with the movement of the population from farms to the cities during the Industrial Revolution. Various foods, such as cod liver oil, were found to prevent or cure the deficiency, eventually leading to the discovery of vitamin D.

Recent large observational data have suggested that ~40% of Europeans are vitamin D deficient, and 13% are severely deficient.

Some reasons why so many may be deficient in vitamin D are:

  • We don't get enough vitamin D in our diet

  • We don't absorb enough vitamin D from food (a malabsorption problem)

  • We don't get enough exposure to sunlight

  • The liver or kidneys cannot convert vitamin D to its active form in the body

  • We take medication that interferes with our body's ability to convert or absorb vitamin D

  • Genetic modifications of VDR

Should I take Vitamin D for my PCOS?

If you are deficient in Vitamin D, it might worsen your PCOS symptoms. I have a list of blood tests I repeat every 3-6 months to keep tabs on how my body is doing. Vitamin D always forms part of that list. I recommend closely monitoring your levels and supplementing accordingly when needed. Even though Vitamin D has a reasonably high threshold for toxicity, I wouldn’t recommend supplementing just for the sake of it.

I hope you enjoyed this newsletter issue. As always, if it has sparked more questions or there is something on your mind you’d like to get clarity on, don't hesitate to submit it here, reply to this email or leave a comment.

See you next Sunday,


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