We all think of getting our vitamin D when we are out in the sun, but what is its importance to health, and who is at risk of deficiency?
Vitamin D is not strictly a vitamin, but actually a pro-hormone that regulates serum calcium concentration by aiding the absorption of ingested dietary calcium in the bowel. If serum calcium levels are low, the body has to maintain adequate levels by mobilising stores from our bones. Therefore, Vitamin D’s primary role is actually involved in bone health, whilst also helping to maintain a healthy immune system, glowing skin, and muscle integrity. Deficiency can result in increased bone turnover leading to reduced bone mineral density, more porous bones, and consequently an increased risk of fractures. However, suboptimal levels of vitamin D are relatively common in the NZ population with an estimated 25% of us having serum levels below the optimal amount. Serious clinical deficiencies in adults can lead to a condition called osteomalacia (softening of the bones), also known as rickets in children.
Vitamin D is the only vitamin whereby we cannot meet our requirements from dietary intake alone. In fact there is very little in food sources. Small amounts can be found in oily fish (e.g. wild salmon, mackerel), products fortified with vitamin D, and mushrooms. The main source is direct sunlight!
As we are now in the middle of winter in NZ, it is important between the months of May to August to try and get sun exposure each day. Around midday is best, with exposure to the face, hands and arms if temperatures allow! Sitting inside in the sun is counterproductive as the UVB required for the metabolic process of generating vitamin D cannot occur. If you are at higher altitudes, such as skiing, ensure you wear sunscreen, and if you have a history of skin cancer, always wear sunscreen. As important as sun exposure is, being sun smart is crucial. So like most aspects of health, balance is key. Skin cancer is the most common cancer in NZ and too much exposure without adequate protection, particularly in the summer months, can be very damaging to the skin (and also leads to wrinkles!).
People at risk of vitamin D deficiency include:
- People who are predominantly indoors, e.g. work, long-stay hospitalisation, institutions.
- Heavy clothing e.g. religious reasons, colder temperatures.
- Locations further from the equator like NZ, particularly in the winter months. This is due to the solar zenith angle with the sun being further away due to the tilt of the earth and this affects how much UV light reaches the earth’s surface. Compared to Europe on equivalent latitudes, NZ has higher UV levels due to the lack of ozone layer. This is good news for vitamin D exposure in winter, but bad news for our skin cancer rates.
People who avoid the sun e.g. history of skin cancer, photosensitising medications, fair skin.
- People with malabsorption syndromes.
- People consuming a low fat diet as vitamins A, D, E, and K are the ‘fat-soluble’ vitamins which can only be absorbed alongside dietary fat.
- Babies who are partially/exclusively breast fed by a mum who is deficient in vitamin D.
If you are worried about deficiency, talk to your doctor. They may suggest a supplement under medical guidance if deemed appropriate. There is a lot of conflicting evidence surrounding vitamin D and its other potential involvement in metabolic disturbances, infections, inflammation, and sports performance as well as discrepancy surrounding a universally defined level for deficiency. Vitamin D definitely needs further research, but there is plenty of exciting work being undertaken, so watch this space!