Vitamin D is a very exciting subject because it’s highly controversial and  with many papers being published, things are moving quickly in this area. Highly renowned medical experts and scientists can’t disagree more when talking about vitamin D.

How to get it

Sunlight exposure is the primary source of vitamin D for most people. Humans produce 90 % of vitamin D naturally as a result of sunlight exposure on our skin — specifically from ultraviolet B (UVB) exposure on the skin. UVB naturally initiates the conversion of cholesterol in the skin to vitamin D3 7-dehydrocholesterol  in the epidermis. And more precisely, it’s the precursor of vitamin D with UVB, which provides the energy to convert the 7-DHC to D.

Vitamin D (whether from the skin or food in the gut) is carried by a vitamin D-binding protein in the blood, first processed in the liver to calcidiol (25-hydroxyvitamin D) and subsequently processed mainly in the kidney to calcitriol (1,25-dihydroxyvitamin D), the active form of vitamin D.

Apart from the sun, the two main ways of getting vitamin D are via diet and oral supplementation. There is also an at-home device available but this delivery method is extremely niche. Although we can find many foods in the supermarket — especially in the US — that have been fortified with a synthetic form of Vitamin D, there are only a select number of foods containing vitamin D naturally, these include oily fish, mushrooms (if UV-exposed), and egg yolks. Most adults are unlikely to obtain more than 10 % of their daily vitamin D intake from food. Oral supplementation appears to be the safest and most efficient way to meet our daily vitamin D requirement.

The oral supplementation of vitamin D is a must in many cases. It is well known that in countries such as the UK, there is a high rate of hypovitaminosis D in the general population in winter and spring as there is insufficient UVB radiation in the winter months. Furthermore, it may be getting worse.

Ann Webb, Professor and Associate Dean for Graduate Education at the University of Manchester, says the UK population is not storing enough vitamin D in the summer months (from April to September), and by starting the winter season already depleted from vitamin D, the winter lows are becoming a significant public health issue.

Sunlight also fails for darker skin types. The darker your skin is, the more UV radiation you will need. Vitamin D synthesis is reduced in those who have dark skin owing to the presence of melanin, which absorbs UV radiation. For people with moderately fair skin, adequate vitamin D levels are likely to be maintained in summer by a walk outside with arms (or equivalent area) exposed for 6–7 minutes mid-morning or mid-afternoon, on most days. In winter the task is more difficult, and in many parts of the country there is only sufficient UVB radiation to produce vitamin D around noon. People with dark skin are likely to need 3–6 times longer sun exposure.

A serious health threat

The need to focus on vitamin D and the role it plays in good health is becoming a very hot topic. It has long been established that a healthy dose of vitamin D will protect us from fractures and help our bone health.

Dr Rebecca S. Mason, a medical endocrine physiologist and Director of the Bosch Institute Faculty of Medicine of Sydney University, says there are enough randomised clinical trials to safely conclude that vitamin D with calcium reduces fractures, falls, improves muscle strength, and reduces the chance of dying over the next 5 years, particularly in people who are deficient.

Dr Richard Weller from the Department of Dermatology, University of Edinburgh, found a correlation in his research between healthy sun exposure and reduced chances of cardiovascular disease and high blood pressure, and found that sunlight could play a role in protecting our heart.

A PubMed database search yielded 63 observational studies of low vitamin D status in relation to cancer risk, including 30 of colon, 13 of breast, 26 of prostate, and seven of ovarian cancer, and a number of studies that assessed the association between the vitamin D receptor genotype with cancer risk.