10 Signs of Low Vitamin D in PCOS (and What to Do About It)

If you’ve been diagnosed with PCOS, or suspect you might have it, you’ve likely heard about the importance of vitamin D. But what’s often missed is just how common low vitamin D levels are in women with PCOS, and the very real impact this can have on your symptoms, from stubborn weight gain to low mood and irregular cycles.

Vitamin D is technically a hormone, not just a vitamin, and plays a key role in how your body manages inflammation, blood sugar, mood, immunity and ovulation. Yet studies show that up to 85% of women with PCOS may have suboptimal levels.

Let’s explore the signs that could suggest your vitamin D levels are low, especially if you have PCOS, and how to support healthy levels safely and effectively.

Why Vitamin D Matters in PCOS

Before we look at the signs, it’s worth understanding why this nutrient matters so much when it comes to PCOS. Research suggests vitamin D can influence:

• Insulin sensitivity – low levels are linked to higher insulin resistance, a core driver of PCOS symptoms

• Androgen levels – vitamin D may help reduce testosterone and improve acne or hair loss

• Ovulation and fertility – sufficient levels are associated with more regular ovulation

• Mood and energy – vitamin D receptors are found in brain areas that regulate mood

• Immune and inflammatory pathways – both of which are often imbalanced in PCOS

10 Signs of Low Vitamin D in PCOS

Many of these symptoms overlap with PCOS itself, which is why vitamin D deficiency can go unnoticed. But if several of these apply to you, it’s worth testing your levels.

1. You feel constantly tired or sluggish

Fatigue is one of the most common, and under-recognised, signs of low vitamin D. If you feel drained no matter how much sleep you get, this could be a red flag.

2. Your mood feels low or flat

Low vitamin D is linked to increased risk of low mood, especially in winter. Women with PCOS may be more sensitive due to underlying inflammation and hormonal imbalances.

3. You catch colds or infections easily

Vitamin D plays a crucial role in immune regulation. Frequent colds, sinus issues or infections may suggest a deficiency.

4. You struggle with sugar cravings or blood sugar crashes

Vitamin D supports insulin sensitivity. Low levels may make it harder to manage cravings, energy dips or PCOS-related insulin resistance.

5. Your periods are irregular (or missing)

While PCOS often causes irregular cycles, low vitamin D can also disrupt ovulation and worsen cycle issues.

6. You’ve been diagnosed with insulin resistance or prediabetes

Multiple studies show a strong link between low vitamin D and poor glucose control, especially in PCOS. If you’ve been told your HbA1c is high or borderline, it’s worth checking your vitamin D too.

7. Your hair feels thinner or you’re experiencing more shedding

Vitamin D is involved in the hair growth cycle. Deficiency can contribute to hair thinning, another concern that’s already common in PCOS.

8. You’ve had fertility challenges

Research suggests that optimal vitamin D levels may improve IVF outcomes, egg quality and ovulation. If you’re trying to conceive with PCOS, it’s an important marker to check.

9. You live in the UK or rarely get sun exposure

In the UK, we can’t make vitamin D from the sun between October and April. If you work indoors, use SPF daily, or cover your skin, your risk of deficiency is even higher.

10. You’ve been told you have low bone density or get frequent aches

Vitamin D helps regulate calcium absorption and bone health. Persistent aches, especially in your lower back or joints, could be linked to deficiency.

How to Test Your Vitamin D Levels

The best way to check your status is with a 25(OH)D blood test. This can be done through your GP or privately as part of functional testing.

Optimal ranges:

• Many UK labs consider >50 nmol/L adequate

• However, functional ranges aim for 75–100 nmol/L for optimal health, especially in conditions like PCOS

Ways to Support Healthy Vitamin D Levels

1.

Supplement wisely

The NHS recommends 400 IU daily as a general maintenance dose. But if your levels are low, you may need a higher dose temporarily (e.g. 1000–2000 IU/day) — best done under guidance after testing. Look for D3 with K2 for better absorption and safety.

2.

Include food sources

Food alone may not be enough, but it helps. Include:

• Oily fish (salmon, mackerel, sardines)

• Free-range eggs

• Fortified foods (plant milks, cereals)

3.

Get safe sun exposure

From April to September, try to get 10–20 minutes of unprotected sun exposure on arms and legs a few times a week, ideally around midday. Balance this with skin safety.

Should You Supplement If You Have PCOS?

In clinic, I often see low vitamin D on blood test results in women with PCOS, even in summer. It’s not just about bones or sunshine. Low vitamin D can quietly sabotage your progress, especially if you’re working hard on food, movement, and hormone support.

That doesn’t mean everyone needs a high-dose supplement, but it’s something I regularly check and personalise based on your symptoms, blood results and lifestyle.

Final Thoughts

Low vitamin D is one of those silent factors that can make your PCOS symptoms feel worse than they need to be, especially fatigue, mood swings, cravings and irregular cycles. The good news is that it’s easy to test and relatively straightforward to improve once you know where your levels stand.

In my 12-week PCOS programme, we often include optional testing for vitamin D and other nutrients, helping you get clear on what your body actually needs and how to support it, without guesswork.

Looking for personalised support?

I am a BANT Registered nutritionist, based in Manchester, working online across the UK. Book a free 30-minute discovery call to explore how nutrition and testing can help you manage PCOS symptoms like fatigue, irregular cycles and cravings, starting with simple, evidence-based steps.

Updated in June 2025 to reflect new PCOS research and nutrition strategies. 

Disclaimer: This content is for educational purposes only and is not a substitute for personalised medical advice. Always check with your GP or healthcare provider before starting new supplements, especially if you’re taking medication or have a medical condition.