Why vitamin D is vital for immunity and fertility

We’ve had SO many questions from readers wanting to know more about which supplements they should be thinking of taking right now, whilst trying to conceive or to support their fertility treatments. We all want to know how we can best prepare our bodies for immunity and fertility, so we thought it was only right to speak to our Partner Nutritionist, Kirsten Oddy about the subject.

Why is vitamin D important?

Vitamin D is well-known for its function in immune health, but there is now increasing evidence of its role with reproductive processes in both men and women too. With approximately 1 in 5 people having low levels of Vitamin D (1), there is no more important time than now to be considering this vital nutrient – for both immune health and reproductive health.

Biological actions of Vitamin D are mediated through Vitamin D receptors that are distributed across various tissues in the body – many are present in various immune cells, but also in various reproductive systems too (2). In females – Vitamin D receptors are expressed in the ovaries, placenta, and endometrium; in males – Vitamin D receptors can be found in smooth muscles of the genital tract, testicular tissue, and sperm (3). The presence of these Vitamin D receptors in reproductive tissues in both males and females suggests Vitamin D plays an important role in the regulation of reproductive processes.

How vitamin D can impact certain aspects of fertility

Ovarian reserve

Vitamin D could have a beneficial effect on anti-mullerian hormone (AMH), a hormone which is produced by cells within the ovary and a useful marker to assess ovarian reserve – and therefore your fertility (5).

Embryo implantation

Reports of high concentration of Vitamin D present in the endometrium in the first trimester of pregnancy suggest it may contribute to embryo implantation (6). Furthermore, a specific gene important for embryo implantation is upregulated by Vitamin D receptors, signifying a possible link to favourable pregnancy outcomes and a reduced risk of preeclampsia and gestational diabetes (7).

Polycystic Ovarian Syndrome (PCOS)

In women with PCOS, Vitamin D deficiency has been associated with obesity, insulin resistance and metabolic and hormonal disturbances (8). Supplementation could improve menstrual frequency and enhance ovulation, in turn resulting in increased fertility outcomes (9). More specifically, recent trials found increased endometrial thickness in women with PCOS receiving Vitamin D during intrauterine insemination cycles (10).

Reproductive immunology

As we already know, Vitamin D is well known for its immune modulating benefits and has been shown to modify the function of natural killer (NK) cells – components of the immune system – to reduce their toxicity. Vitamin D could also help to reduce circulating antiphospholipid antibodies associated with poor reproductive outcomes (11).

IVF outcomes

For women undergoing in-vitro fertilisation (IVF), sufficient vitamin D levels should be maintained. Optimal vitamin D levels have an association with success in achieving a clinical pregnancy in IVF (12). This has mainly been attributed to vitamin D’s effects on the endometrium, but genetics could also play a role in this relationship.

Sperm health

Decreased Vitamin D levels have been associated with poor semen quality and abnormal motility and morphology (13). Moreover, Vitamin D deficiency is also associated with reduced testosterone levels which can directly affect fertility by causing decreased sperm production and indirectly by reducing sex drive and causing erectile dysfunction (14).

How to increase vitamin D levels

Vitamin D is found naturally in small amounts in a few foods that help fertility:

• Oily fish – such as salmon, sardines, herring and mackerel
• Red meat
• Liver
• Eggs
• Fortified foods – such as some dairy free milks and cereals

Vitamin D is also known as the ‘Sunshine Vitamin’ as we get the majority of our Vitamin D from sunlight – our skin absorbs the UVB light and it converts to Vitamin D in the body. Most people should be able to get the majority of their Vitamin D they need from sunlight during Spring and Summer months, however when sunlight exposure is low – especially during Autumn and Winter months and now when many people are self isolating – we should be increasing our dietary intake of Vitamin D and considering supplementation too.

Supplementing with Vitamin D could represent a beneficial and inexpensive therapeutic approach to female infertility in combination with other therapies and treatments, however it is important to be aware that long term supplementation of this vitamin can have negative consequences (15). It is therefore always recommended to test your Vitamin D levels regularly and work closely with a nutritionist to ensure you are not putting your health at risk.

See Kirsten’s previous article on ‘How to strengthen your immune system’ or ‘Could poor gut health be contributing to infertility?’