Low levels of vitamin D have been linked to cancer, heart disease, diabetes, dementia and arthritis, as well as childhood illnesses. So is sunshine and oily fish enough – or should you take supplements?
Vitamin D, the so-called sunshine vitamin, is rarely out of the news. Take the past fortnight: a study published in the American Journal of Clinical Oncology found that people with low levels of vitamin D died or relapsed earlier from a type of non-Hodgkin lymphoma. The University of Florida showed that taking vitamin D supplements reduces pain and improves function in obese people with osteoarthritis. Conversely, Finnish scientists established that exercise reduces injury from falls in septuagenarian women significantly more than vitamin D supplements do.
Vitamin D deficiency has been inconclusively linked to numerous conditions, including breast, bowel, lung and prostate cancers, heart disease, type 2 diabetes, dementia and rheumatoid arthritis. In fact, research on the topic was recently described by a Harvard medical professor as “the wild, wild west”. Amid the fog of conflicting studies, the big news story that doctors in the UK were expecting last month has been postponed until after the election. The government’s Scientific Advisory Committee on Nutrition (SACN) was due to release its first report on vitamin D since 2007. The consensus is that the volume and ever-changing nature of the research to be waded through has rendered their job almost impossible, although some believe that this most recent delay (not the first) is political – perhaps an expensive mass supplementation programme is on the cards.
Vitamin D is essential for calcium absorption, and some people in the northern hemisphere aren’t getting enough sun exposure to produce what they need, or aren’t supplementing levels sufficiently through diet (oily fish is one of the best sources). But we still don’t know the true scale of the problem. Meanwhile, the affluent worried well are already merrily popping vitamin D capsules as a lifestyle choice. Even if you’re not deficient, the standard daily supplement dose (400iu for children, 1,000iu for adults) is unlikely to do you any harm – although it can be toxic in vast amounts. Whether or not you’re wasting time and money is harder to tell.
Without having an expensive blood test, it is impossible to know what your vitamin D levels are. All you can do is make a guess based on your age, sun exposure, skin colour and diet. Even if you do know what your vitamin D levels are, few experts can agree on what is deficient, optimum or too much. “We know that below a blood level of, say, 30nmol/litre, there is a high risk of rickets and its adult equivalent, osteomalacia,” says Kay-Tee Khaw, of the University of Cambridge’s department of public health and primary care. “Everyone agrees on that, and if you have low levels you should supplement.” The debate comes at middling levels, between 30 and 100nmol/litre.
One academic expert in this area, who prefers not to be named, says he chose not to supplement his children because he prefers to focus on a healthy diet and lifestyle. He likens the rise in vitamin D supplementation to the recently debunked “magic supplement” status of antioxidants.
Sport may be one area where unnecessary supplementation is rife. Vitamin D levels below 30nmol/litre cause muscle weakness. Khaw says: “30-50nmol/litre is probably a bit below optimum, which is where most of us are, and some people think that you should be above 50.” The question is, she says: “If you go from 50 to 100, is that better for your muscles? That is very controversial. There is not much good evidence that going above deficiency is better for your muscles.”
Government advice is that pregnant and breastfeeding women, the over-65s and children from six months to five years old should take vitamin D supplements. However, although prescriptions are free for these groups, vitamins often aren’t included because they’re not classed