The new research suggests strongly that blood levels of vitamin D are a good barometer of overall health. But it does not resolve the question of whether low levels are a cause of disease or simply an indicator of behaviours that contribute to poor health, like a sedentary lifestyle, smoking and a diet heavy in processed and unhealthful foods.
Vitamin D helps the body absorb calcium and is an important part of the immune system. Receptors for the vitamin and related enzymes are found throughout cells and tissues of the body, suggesting it may be vital to many physiological functions, said
Dr Oscar H Franco, a professor of preventive medicine at Erasmus Medical Center in the Netherlands and an author of one of the new studies, which appeared in the journal BMJ.
It has effects at the genetic level, and it affects cardiovascular health and bone health, he said. There are different hypotheses for the factors that vitamin D regulates, from genes to inflammation. Thats the reason vitamin D seems so promising.
The two studies were meta-analyses that included data on more than a million people. They included observational findings on the relationship between disease and blood levels of vitamin D. The researchers also reviewed evidence from randomised controlled trials the gold standard in scientific research that assessed whether taking vitamin D daily was beneficial.
Dr Franco and his co-authors a team of scientists at Harvard, Oxford and other universities found persuasive evidence that vitamin D protects against major diseases. Adults with lower levels of the vitamin in their systems had a 35 per cent increased risk of death from heart disease, 14 per cent greater likelihood of death from cancer, and a greater mortality risk overall.
When researchers looked at supplement use, they found no benefit to taking vitamin D2. But middle-aged and older adults who took another form, vitamin D3 found in fish and dairy products and produced in response to sunlight had an 11 per cent reduction in mortality from all causes, compared to adults who did not.
In the United States and Europe, it is estimated that more than two-thirds of the population is deficient in vitamin D. In their paper, Dr Franco and his colleagues calculated that roughly
13 per cent of all deaths in the United States, and 9 per cent in Europe, could be attributed to low vitamin D levels.
We are talking about a large part of the population being affected by this, he said.
Vitamin D could be a good route to prevent mortality from cardiovascular disease and other causes of mortality.
In the second study, also published in BMJ, a team of researchers at Stanford and several universities in Europe presented a more nuanced view of vitamin D.
They concluded there was suggestive evidence that high vitamin D levels protect against diabetes, stroke, hypertension and a host of other illnesses. But they also said there was no highly convincing evidence that vitamin D pills affected any of the outcomes they examined.
- ANAHAD O'CONNOR