Vitamin D

Vitamin D may not be the first supplement to be called a "wonder vitamin", but it is one of the few to have lived up to the name. The biggest review of the role of vitamin D in health found that people who took supplements of the vitamin for six years reduced their risk of dying from all causes.
Earlier studies had suggested that vitamin D played a key role in protecting against cancer, heart disease and diabetes. The new study shows that it does.
Vitamin D is important because we are often short of it. Most healthy individuals get all their nutrients from eating a balanced diet, but vitamin D is the exception. Vitamin D is made by the action of sunlight on the skin.
In the winter, the sun in Britain is barely strong enough to make vitamin D, and by spring, say scientists, 60 per cent of the population is deficient.
Giving vitamin D to a group of volunteers reduced colds and flu by 70 per cent over three years. All the participants were Afro-Caribbean women who make less vitamin D.
Differences in sunlight may help explain the higher rates of heart disease in Britain compared with southern Europe.
A study of almost 10,000 women over 65 found that those who took vitamin D had a 31 per cent lower risk of dying of heart disease; less vitamin D was found in patients with chronic heart failure.
Vitamin D lowers insulin resistance, which is one of the major factors in heart disease. Vitamin D is also used by the thyroid, which secretes a hormone that regulates the body's levels of calcium, which in turns helps regulate blood pressure.
A 40-year review of research found that daily vitamin D could halve the risk of breast and bowel cancer. Scientists reviewed 63 scientific papers and concluded that there was a need to boost vitamin D levels. They said that a daily dose of 1,000 iu was needed; the recommended level in the US is currently only 400 units.
The research showed that African Americans with darker skins and people living in the north-eastern US, where it is less sunny, were more likely to be deficient in vitamin D, and had higher cancer rates.
Rickets is caused by vitamin D deficiency. Cod liver oil, which contains vitamin D, virtually eliminated the condition. Now, rickets is reappearing. Doctors in Dundee reported five cases recently in ethnically Asian children; dark skin produces vitamin D more slowly than lighter skin.
Vitamin D is crucial for the absorption of calcium, which is the building material for new bones. As well as leading to rickets, deficiencies can contribute to poor tooth formation, stunted growth and general ill health.
NICE is consulting on a proposal to recommend supplements for certain pregnant women at risk: vegans and women who cover their skin for religious reasons. Vitamin D supplements are already recommended for infants at risk.
Vitamin D supplements given to Finnish babies reduced their risk of Type 1 diabetes by 80 per cent. Researchers followed 12,000 children and found that those with rickets, indicating vitamin D deficiency, were three times more likely to become diabetic. Vitamin D is believed to act as an immunosuppressive agent, which may prevent an auto-immune response from destroying insulin-producing cells in the pancreas.
Sir Donald Acheson, former UK Chief Medical Officer, published a study in 2004 suggesting that people who spent more time in the sun had a lower risk of multiple sclerosis than those who stayed out of it. It concluded that a certain level of exposure to the sun might be necessary throughout the year.
John Cannell, a psychiatrist and vitamin D advocate, thinks that medical advice to avoid the sun and cover up since the 1980s has paralleled the rise in autism. Flagging levels of vitamin D could be the decisive factor. Vitamin D can be obtained by getting enough unfiltered sunlight (which means getting outside wearing as little as possible consistent with decency) but possibly a more reliable means is to take cod liver oil or vitamin D supplements.