The power of Vitamin D
Vitamin D is frequently referred to as the ‘Sunshine Vitamin’ as sunlight is necessary for the synthesis of this vitamin (which is produced underneath the skin following exposure to sunlight). Vitamin D occurs in two forms: vitamin D2, which is found in a small amount in some foods, and vitamin D3, which is formed in the skin when exposed to sunlight. Both D2 and D3 are converted into a form that the body can use in the liver and the kidneys. People need varying degrees of vitamin D depending on where they live and their diets.
Every cell in your body has a receptor for vitamin D, which makes it more like a hormone than a vitamin. It boosts your immune health and can help people with autoimmune diseases.
Vitamin D also allows the body to absorb calcium, and this is why women with low vitamin D levels could be at a higher risk of osteoporosis. Not to mention how our mood changes when there’s less sunshine.
As Vitamin D can only be found naturally in small amounts in only a few foods, in order to make vitamin D more available, it is added to dairy products, juices, and cereals that are then said to be ‘fortified with vitamin D’.
In the UK (and throughout the northern hemisphere) we often don’t get enough of the type of sunlight that causes our bodies to manufacture vitamin D under the skin. Only one kind of solar radiation does this: UVB sunlight. Vitamin D is synthesised only when we’re exposed to UVB rays – and unless UVB rays are present it doesn’t matter how warm it is, or in fact how brightly the sun is shining: your skin cannot synthesise vitamin D. And so, in the UK, where we are often only exposed to UVB from April to October, it is likely that many people will be deficient in vitamin D during the winter months.
It is the opinion of Harvard Medical School that ‘Except during the summer months, the skin makes very little if any, vitamin D from the sun at latitudes above 37 degrees north or below 37 degrees south of the equator. People who live in these areas are at relatively greater risk for vitamin D deficiency’.
Why is vitamin D important?
- for the normal absorption/utilisation of calcium and phosphorus
- it contributes to normal blood calcium levels
- for the maintenance of healthy bones and teeth
- for the maintenance of normal muscle function
- it contributes to the normal function of the immune system
- it plays a role in the process of cell division
- it is needed for normal growth and development of bone in children
In addition, Vitamin D is used in the treatment of conditions of the heart and blood vessels, including high blood pressure and high cholesterol. It is also used for diabetes, obesity, muscle weakness, multiple sclerosis, rheumatoid arthritis, chronic obstructive pulmonary disease (COPD), asthma, bronchitis, premenstrual syndrome (PMS), and tooth and gum disease. Some people use vitamin D for skin conditions including psoriasis, actinic keratosis, and lupus vulgaris. More recently the importance of vitamin D has been recognized as a significant factor in relation to fertility, although there is still a lot more research to be done.
Although the recommended daily dose of vitamin D is 400 international units (IU), new research suggests taking at least 10micrograms (10ug) of vitamin D daily to ensure you receive all the health benefits. And while sunshine is the best source of vitamin D, you can still top up on the vitamin by adding vitamin D-rich foods to your diet.
Vitamin D and fertility
In the world of fertility, the importance of vitamin D has been studied in experiments involving mice. These studies have shown us that mice that are vitamin D deficient or lack a vitamin D receptor have an underdeveloped uterus or an inability to form mature eggs. If a pregnancy did occur in these mice the foetus produced often showed impaired growth. With vitamin D supplementation reproduction is returned to normal in mice but not by giving calcium alone – suggesting that vitamin D’s role in female reproduction is not related to the ability to absorb calcium.
In humans, the vitamin D receptor is present in many female organs including the uterus, ovary and placenta.
The active form of vitamin D (D3) has various important roles in human reproduction. It is able to control the genes involved in making oestrogen. It also controls several genes involved in the implantation of the embryo. Once a woman is pregnant vitamin D3 is involved in the organisation of the immune cells in the uterus. During pregnancy, if a woman is deficient in vitamin D it has been linked to some complications such as diabetes and hypertension.
In men, vitamin D level has been associated with semen quality and sperm count, motility and morphology. There is evidence to suggest that if a male is not deficient in vitamin D then there is a positive effect to be seen on semen quality, testosterone concentrations and fertility outcomes. Further studies are required in this area.
IVF and vitamin D
Research surrounding assisted reproduction has contributed to the study of the role of vitamin D during preconception, and from egg development to implantation of the embryo. In a recent study it was discovered that women with higher vitamin D levels were significantly more likely to achieve a pregnancy with IVF compared to women with lower levels of vitamin D.
The study was repeated at a different IVF unit and it was found that there was a fourfold difference in pregnancy achievement between those with sufficient vitamin D levels in comparison those women who were deficient. Further research is needed into this emerging evidence that vitamin D levels may be linked to IVF success.
Which foods are good sources of vitamin D?
- Egg yolk
- Cod and halibut liver oils
Anagnostis P, Karras S, Goulis DG (2013). Vitamin D in human reproduction: a narrative review. Int J Clin Pract;6 7(3):225-35.
Ozkan S, Jindal S, Greenseid K, Shu J, Zeitlian G, Hickmon C, Pal L (2010) Replete vitamin D stores predict reproductive success following in vitro fertilization. Fertility and Sterility; 94(4):1314-9.
Rudick B, Ingles SA, Stanczyk F, Chung K, Paulson R, Bendikson K (2010) Characterizing the role of vitamin D levels on IVF outcomes: stimulation, embryo, or endometrium? O-245, Annual Meeting of the American Society for Reproductive Medicine.
Scientists recommend we need to triple our daily vitamin D intake. Science Advisory Committee on Nutrition (SACN): https://www.sheffield.ac.uk/news/nr/scientists-say-we-need-to-triple-our-vitamin-d-intake-1.592505 – 20 July 2016.