Shadow cast over expert advice on sunshine and vitamin D

Shadow cast over expert advice on sunshine and vitamin D

There is little chance of leading a truly simple life today because so much of it is done with the advice of experts. When it comes to safe driving, it is the likes of the Department of Transport or the AA; with food, we are bombarded with nutritional tips; and there is no shortage of instruction on how to bring up our children.

We tend to believe the advice of people with a good track record and evident qualifications. But sometimes they get it wrong, sometimes they disagree, and that is where the simple life ends. Take dermatologists, who, over the years, have advised and frightened people into avoiding the sun. There is a link between excessive sun exposure and melanoma, the form of skin cancer that carries a high risk of death.

But the link is not clear cut. Melanoma occurs in the mouth, the anus and on the soles of the feet, areas that get little or no sun, as well as on the face, which may get a lot. So the relationship with the sun is not obvious. And despite what dermatologists tell us, the evidence shows that in the UK people are less likely to get melanoma if they spend weekends mostly outdoors, where they inevitably get more sun exposure.

People who stay inside have low sun exposure, low vitamin D (made in the skin when it is exposed to sunshine) and are at greater risk of several kinds of cancer. So it is a good idea to take vitamin D supplements, at least 2,000 units a day, especially in winter.

However, The Lancet, the world’s best-known medical journal, recently suggested in an editorial that most of the benefits of vitamin D advanced by scientific studies are a “myth”. It says that people tend to have low vitamin D when they are ill because they do not go outdoors very much.

This was also the view presented in papers published in The Lancet by two teams, Philippe Autier of the International Prevention Research Institute, Lyon, and Mark Bolland of the Department of Medicine, University of Auckland. They argue that clinical trials of vitamin D have failed to show any clear benefit. However, most of the trials have used low doses of the vitamin. Professor Michael Holick, pioneer of vitamin D research at Boston University, says 4,000 units per day is required to give an optimum level of the vitamin in the blood, enough to prevent disease. A number of clinical trials relied on by The Lancet editorial and its authors used a daily dose of just 400 units.

The Lancet and its authors have also, in my view, used defective scientific reasoning based on what statisticians call a “type 2 error”. They have over-generalised a result that only has a narrow basis in fact. A negative result in a clinical trial of vitamin D supplementation in adults cannot be generalised because it cannot rule out damage caused by vitamin D deficiency many years earlier that is irreversible. Adult disease may be caused by deficiency of vitamin D occurring in childhood or teenage years and such disease may not be remedied by giving the vitamin later.

This is the case with rickets, a bone deformation in children caused by lack of both sunshine and vitamin D. Rickets may be corrected if vitamin D is given to a child. But once bones stop growing in adulthood deformities become fixed and cannot be changed by giving vitamin D. I have explained these errors in more detail in a peer-reviewed article in Public Health Nutrition (

There is good evidence to suggest that a shortage of vitamin D in the womb and early life may be a cause of three serious diseases: multiple sclerosis, type 1 (juvenile) diabetes, and autism. Heart disease and a number of cancers are also linked to insufficient vitamin D at various life stages. This, at least, is the view of a large number of experts who have published their findings.

It can be difficult to decide where the truth lies when experts disagree, but not when, as in The Lancet’s vitamin D articles, the argument depends upon a basic statistical error.

by Oliver Gillie,

The Telegaraph, Monday 24 November

View more