Vitamin D & Fertility

Vitamin D has gained a reputation as ‘the sunshine vitamin’, but behind the glamorous nickname, what has vitamin D got to do with your fertility? 

What's the sun got to do with it?
Vitamin D has  earned its  title as the  sunshine vitamin because the  sun  does play an important role  in ensuring our body gets  enough of it. Vitamin D is found in its ‘dormant’ form, a molecule called 7-dehydrocholesterol, in the outermost layer  of the skin: the epidermis. The dormant molecule needs UV light, which it gets from sun exposure, to convert the ‘dormant’ form into a usable form of the  vitamin. We call this Vitamin D3. In the UK, it has been calculated that the average person does not get enough daily sunlight to synthesise adequate D3 through  the winter months. Furthermore, if you dress modestly due to religion you are unlikely to get enough  sunlight. People who have increased melanin (darker skin tone), greater body fat mass or older skin are also at risk of not getting enough sunlight, as they need proportionately more to synthesise that same amount of vitamin D. 

Of course, if you could get all of your required vitamin D from the sun, I probably wouldn't be writing about it. So here's the catch: we get about 80% of our required Vitamin D from the skin, but have to make up the difference with our diet. It is highly recommended that Vitamin D supplements are taken by all adults, especially women trying to conceive, pregnant or breastfeeding. Generally 10mcg per day is enough, though if you are at a ‘high risk’ of deficiency, such as having darker skin, BMI >30 or limited sun exposure, you may benefit from a higher dose. Current studies are finding benefits of 25mcg per day, but this is yet to be made an official recommendation. 

Food vs Supplement:
Vitamin D is found naturally in some foods, such as salmon and oily fish, egg yolks, meat and mushrooms. However, Vitamin D is quite ‘unstable’ which means it deteriorates when exposed to heat or moisture. So even foods that naturally contain a lot of vitamin D  may not be providing quite enough. That is why supplements are recommended too. Supplements may come in the form of D2 or D3; both are good, usually D2 is the vegan source (often made from mushrooms or algae) and D3 can be synthesised from animal sources, such as sheeps wool. You may also find ‘Vitamin D + Calcium’ supplements, these are great too as vitamin D and calcium work together to get absorbed better. 

All this makes sense… but why?
It often helps to understand the importance of a supplement when you're taking it. Here's a brief overview of the role of vitamin D in the body:

• Promotes osteoblast differentiation to help form new bone tissue, keeping bones healthy and reducing risk of weak bones

• Stimulates calcium absorption in the intestines

• Inhibits production of cytokines (protein) which cause inflammation

• Modulates immune responses to infection 

• Some new research points to Vitamin D reducing risk of autoimmune conditions, but much more evidence is needed here

About fertility:
It is widely accepted that vitamin D plays a role in hormone synthesis in women, particularly of sex hormones like oestrogens. One study found that as blood vitamin D levels improve towards desirable range, levels of testosterone and LH decreased - these are hormones which are often found to be too high in women with PCOS.  However, there is some controversy regarding what an ideal dose of Vitamin D is, so more studies are needed. Despite this, it has been well understood that low levels of vitamin D are linked to poor maternal and foetal outcomes such as pre-eclampsia, gestational diabetes and low birth weight. In men, some studies have found a link between low Vitamin D status and low sperm count; though this is an association not a causal link, so more research is needed. 

All in all, it is likely to be worth having a vitamin D supplement if you are trying to conceive, in order to avoid potential complications and maintain a good nutritional status. If you have concerns about your vitamin D intake or have any questions about your nutrition, you can contact us via social media or our website. 

References:
DOI: 10.1001/archderm.1987.01660360108022
DOI: 10.3390/nu10101498
DOI: 10.231/JIM.0b013e31821b8755
DOI: 10.1136/bmj-2021-066452
DOI: 10.1007/s11154-017-9407-2