This was an interesting couple of weeks for vitamin D. First we had a negative headline suggesting that the third of men and just under half of women who take vitamin D supplements in Britain are wasting their time. Then, in the same newspaper, headlines claimed that ‘Britons are not getting enough vitamin D from sunlight, putting us at risk of deadly ailments’.
So what is the truth? Do you need a supplement or not? The answer is, of course, an unequivocal ‘Yes’. And it’s not just me saying that, it’s the Scientific Advisory Committee on Nutrition (SACN) and Public Health England. Although you can make some vitamin D in your skin on exposure to sunlight, this only occurs when the UV index is at least 3 – something which at UK latitudes only occurs during Spring and Summer, and then only on sunny days.
Vitamin D and sunshine
Usual advice is to obtain 10 to 15 minutes sun exposure to your face, arms, hands or back, two or three times a week, without sunscreen. Longer exposures do not provide additional benefit, as vitamin D is rapidly degraded by excess UV radiation (and your risk of skin cancer increases).
Even when the sun is shining, however, not everyone produces vitamin D efficiently. Among fit, healthy surfers in Hawaii, for example, more than half were found to have low vitamin D levels despite achieving 29 hours of sunshine exposure per week. This is partly due to genetic factors and partly due to the fact that, after 15 to 20 minutes UV exposure, the vitamin D you make is rapidly degraded by excess UV radiation. The efficiency with which you synthesise vitamin D also reduces with age so that, by the time you are in your 60s, you make 4 times less vitamin D in your skin that you did in your 20s.
Once you slap on sunscreen, a properly used SPF8 reduces vitamin D production in your skin by 95%, while SPF15 reduces vitamin D production by 99%. Most people do not apply enough sunscreen, however, and the development of a tan suggests that enough UVB radiation strikes the skin to stimulate production of both melanin (a natural sunscreen produced in response to UV damage) and some vitamin D regardless of sunscreen use.
How much vitamin D do you need?
The current, recommended intakes for vitamin D were set when its only recognised role was in promoting calcium and phosphate absorption and maintaining healthy bones and teeth. Now, vitamin D is recognised as important for preventing a number of diseases through its effects on cell signalling and communication.
Vitamin D deficiency is well-known to affect bones, leading to rickets in children and osteomalacia in adults, but growing evidence suggests lack of vitamin D also increases the risk of osteoporotic fractures, heart failure, multiple sclerosis, dementia, infections and even cancer.
Pooled results from 18 clinical trials, involving over 57,000 people, for example, have shown that taking vitamin D supplements (300 IU to 2000 IU daily, average 528IU) was associated with a 7% reduced risk of dying from any medical cause over the average follow-up period of 5.7 years.
It’s therefore timely that supplement recommendations are getting updated. According to Public Health England, as many as one in five adults and one in six children have low vitamin D levels in the UK – representing 10 million people in England alone.
Vitamin D from food and supplements
Dietary sources of vitamin D3 (the animal-based form) include liver, cod liver oil, oily fish such as salmon, sardines and mackerel, red meat, egg yolks, fortified margarines and breakfast cereals. Vegetarian sources provide a form known as vitamin D2 which has less than a third of the potency of vitamin D3 and is less efficient at maintaining blood levels.
The EU recommended daily amount (RDA) for vitamin D is just 5mcg (200 IU) per day, while the US DV is 10mcg. Public Health England recommend that everyone takes a supplement supplying 5mcg vitamin D per day, but that is very much a minimum to prevent deficiency diseases. Genetic factors mean that many people, and those who are older and make vitamin D less efficiently, require 25mcg (1000 units) or more per day to maintain a healthy blood level – especially during winter months.
Although vitamin D is fat-soluble, and can be stored in the body it is a relatively safe supplement to take with the European Food Safety Authority suggesting a tolerable upper intake level of an Upper Tolerable Level of 100 mcg vitamin D per day (4000 IU). Toxic effects can occur at intakes exceeding 500 mcg per day, including headache, loss of appetite, nausea, vomiting, diarrhoea or constipation, palpitations and fatigue.
Choose a vitamin D3 supplement labelled as produced according to a pharmaceutical standard known as GMP (Good Manufacturing Practice) to ensure they are checked throughout manufacture for purity and consistent dosing.
Image credits: julie_falk/flickr