Vitamin D deficiency – the probable cause of many diseases?
“Gold standard” trials quoted by the Lancet rely on mistaken reasoning.
The Lancet, the world’s best known medical journal, has published two articles which contain serious errors in scientific reasoning. The articles making these errors argue that the association between vitamin D deficiency and various diseases, which include certain cancers, is not caused bythe deficiency but isthe result of “reverse causation”. They suggest that people with these illnesses spend less time in the sun and so their vitamin D level is low, and their illness is caused by something else.
The reasoning is in error because a negative result in a clinical trial of vitamin D supplementation only shows that the vitamin cannot heal a particular group of people. Itcannot be generalised to people of all ages and types, argues scientist and writer, Oliver Gillie, in an articlepublished in the journal, Public Health Nutrition.
The Lancet authors point to clinical trials of vitamin D in a number of diseases,all with negative findings. They argue that negative clinical trials show that vitamin D cannot be the cause of any of these diseases. The Lancet and its authors insist that their trials are “gold standard” evidence and The Lancet backs up their authors with an editorial called“Vitamin D: chasing a myth?”
“They have made a mistake in scientific reasoning known to statisticians as type 2 error. I would like to call it the gold standard fallacy”. said Dr Gillie.
As Dr Gillie argues in his article, the Lancet and its authors overlook the fact that adult disease may be caused by deficiency of vitamin D occurring in childhood or teenage years, and that 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 sunshine and lack of vitamin D. Rickets may be corrected if vitamin D is given in childhood when growth is still occurring. But once bones stop growing, adulthood deformities become fixed and cannot then be changed by giving vitamin D.
A number of other diseases are known or believed to be caused by insufficient vitamin D in childhood. Dr Gillie also discusses the example of multiple sclerosis, which is known to be more common in northern countries with short summers and hence less exposure of people to the sun. For a long time experts researching multiple sclerosis resisted the suggestion that vitamin D might be a factor in the disease. But now much more evidence has accumulated and experts believe that deficiency of vitamin D is the major cause of MS.
However the Lancet authors point to clinical trials in which adults with MS have been given vitamin D without any clear improvement in their health and they argue from this that D deficiency cannot be the cause of the disease. This is mistaken
scientific reasoning, Dr Gillie asserts, a type 2 statistical error; because statistical tests specify very precise conditions and can never prove a lack of difference between two groups to be true for all conditions and all groups.
Read the full article here until 3rd December 2014.