Vitamin D and fertility: can supplements help you conceive?

What the expert says:

We asked our expert GP Dr Philippa Kaye about vitamin D and conception. She said:

Vitamin D, by itself, won't help you conceive. But there is some evidence in both animal and human studies to suggest that vitamin D may affect fertility and IVF success rates
Dr Philippa Kaye

Dr Kaye says the science isn't strong enough to confirm a definite, causal link between having good levels of vitamin D and conception success. But she also points out that there is strong evidence that vitamin-D deficiency is associated with pregnancy complications (including gestational diabetes and pre-eclampsia⁴) – which is why pregnant women are advised to take vitamin-D supplements.

And, as vitamin-D insufficiency is really common in the UK, anyone planning to get pregnant may want to get a headstart.

Pregnant women are advised to take 10mcg vitamin D (400 UI) a day throughout the whole of pregnancy, so it may be worth starting while you are trying to conceive
Dr Philippa Kaye

Can vitamin D improve my IVF chances?

Several observational studies have suggested that women seem to have a better IVF outcome when their vitamin-D levels are 'sufficient'. In 2018, a review of 11 of these studies,⁵ on 2700 women, confirmed these findings, saying "the chances of achieving a live birth, a positive pregnancy test and clinical pregnancy [after IVF] are higher in women who are vitamin-D replete when compared to those who are vitamin-D deficient or insufficient".

The British scientists leading this review warned, however, that, though they'd found a link between good levels of vitamin D and successful IVF treatment, it was only an 'association' and clinical trials would have to be carried out before anyone could say that 'correcting' a woman's vitamin-D levels before starting IVF would increase her chances of having a baby.

Can vitamin D help reduce my fibroids?

Fibroids – or, more correctly, uterine fibroids – are non-cancerous growths in your womb. They are quite common (affecting 1 in 3 women at some point in their life⁶) but often cause no symptoms at all. However, if you have a large fibroid, it can make it difficult to get pregnant, as the fibroid may block 1 of your Fallopian tubes (through which your egg needs to travel to your womb) or prevent your fertilised egg attaching itself to the lining of your womb.

Dozens of small studies have suggested that vitamin D can inhibit the growth of fibroids. And in 2018 a review of 45 of these studies⁷concluded that "vitamin D and its analogues seem to be promising, effective, and low-cost compounds in the management of [fibroids] and their clinical symptoms".

But again, the review authors state that more research is required before "vitamin D preparations can become the new tools in the fight with fibroids".

Can vitamin D regulate my menstrual cycle?

If your periods are not regular, it can be more difficult to get pregnant⁷because you might not ovulate (release an egg) regularly.

There are some studies^8,9 that suggest a link between low levels of vitamin D and what researchers call 'menstrual disorders' but, again, further research has been called for.

Can vitamin D help with my PCOS?

Polycystic ovary syndrome – or PCOS – is a common condition that can affect ovulation and menstruation, and so make it difficult to get pregnant.

Among the studies into the role of vitamin D and menstrual cycles (see Can vitamin D regulate my menstrual cycle?, above), there are some observational studies that specifically focus on women with PCOS – with a range of results. A 2015 overview¹⁰, published in the Indian Journal of Medical Research, says, "So far, the role of vitamin D polymorphisms on metabolic disturbances in women with PCOS remains inconclusive. Further investigations... are necessary."

Although it's far from proved, then, that vitamin D supplements may help fertility issues caused by PCOS, we do have some anecdotal evidence from our MadeForMums community that they might.

Charlotte says: "I was diagnosed with PCOS at 17, didn’t have my 1st period until I was 24 and between then and now (4 years later), I've had a total of 10 periods. My partner and I have never used any contraception: we took the view that it would never happen naturally. A year ago, we started the process of getting fertility treatment but, for one reason or another, it kept getting put on hold. I started to do some research into natural supplements I could take and came across information about vitamin D and fertility. I thought, what harm could it do? I started taking them daily. Lo and behold, 3 months later, I fell pregnant naturally! This could be a complete coincidence but, with how irregular I was, I really feel it played a part."

Are there other reasons for taking vitamin D supplements if I'm trying to get pregnant?

It's not proven, as we've seen, that taking vitamin D supplements will make it any easier or quicker for you to conceive. But, particularly in the winter months, they can do you good, in terms of your general health and many doctors, including Dr Philippa, do recommend taking them from September to March anyway.

And it won't do you any harm (unless your GP advises that it's specifically not recommended in your medical circumstances).

Why particularly in the winter months? Current NHS advice is that every adult needs 10 mcg vitamin D a day.² In the spring and summer, our bodies should be able to 'make' that much vitamin D naturally, as long as we eat a balanced diet and we're outside long enough for our skin to absorb sufficient direct sunlight. But, between September and March, when the sun isn't so strong and we don't go outside as much, our bodies may struggle to make that much vitamin D.

That's why everyone in the UK is advised to consider taking a supplement of vitamin D between September and March²– and people who have black or pigmented skin, who aren't able to go outdoors or aren't able (for cultural, medical or religious reasons) to uncover their skin outdoors are often advised to take a vitamin D supplement all year round.

Additionally – because low or deficient vitamin D have been shown to increase the risk of some pregnancy complications⁴ – women who are pregnant or breastfeeding are also advised to take a vitamin D supplement every day, regardless of the time of year.

If I'm taking vitamin D supplements, is it safe to take more than the recommended daily dose?

The recommended daily dose of 10mcg should be all that you need – although, if blood tests show you are very vitamin-D deficient, your GP may provide you with a large dose for a short period of time.

It's important, though, not to take higher doses without medical supervision or for a long period of time. Taking too much vitamin D can cause too much calcium to build up in your body (a condition called hypercalcaemia)². This can weaken your bones and damage your kidneys and heart.

About our expert GP Philippa Kaye

Dr Philippa Kaye works as a GP in both NHS and private practice. She attended Downing College, Cambridge, then took medical studies at Guy's, King's and St Thomas's medical schools in London, training in paediatrics, gynaecology, care of the elderly, acute medicine, psychiatry and general practice. Dr Philippa has also written a number of books, including ones on child health, diabetes in childhood and adolescence. She is a mum of 3.

Pics: Getty

References

^{1 Vitamin D Insufficiency Among Free Living Healthy Young Adults. Tangpricha V et al. The American Journal of Medicine. Volume 112, Issue 8, Pages 659–662. DOI: https://doi.org/10.1016/S0002-9343(02)01091-4
2. Vitamin D: NHS online
3. Vitamins, supplements and nutrition in pregnancy: NHS online
4. Association between maternal serum 25-hydroxyvitamin D level and pregnancy and neonatal outcomes: systematic review and meta-analysis of observational studies. Aghajafari F et al. BMJ 2013 Mar 26;346:f1169. doi: 10.1136/bmj.f1169.
5. Vitamin D and assisted reproductive treatment outcome: a systematic review and meta-analysis. Chu, J. Human Reproduction, Volume 33, Issue 1, January 2018, Pages 65–80, https://doi.org/10.1093/humrep/dex326
6. Fibroids: overview. NHS online
7. Vitamin D and Uterine Fibroids — Review of the Literature and Novel Concepts Ciebiera M et al. International Journal of Molecular Sciences. DOI: 10.3390/ijms19072051
8. The Relationship between Vitamin D Status and the Menstrual Cycle in Young Women: A Preliminary Study Łagowska, K. Nutrients 2018. DOI: 10.3390/nu10111729
9. Lower plasma 25-hydroxyvitamin D is associated with irregular menstrual cycles in a cross-sectional study. Jukic, AM et al. Reproductive Biology and Endocrinology 2015; 13:20. doi: 10.1186/s12958-015-0012-5
10. The role of vitamin D in polycystic ovary syndrome. Lin MW et al. Indian Journal of Medical Research 2015 Sep; 142(3):238-240. doi: 10.4103/0971-5916.166527}