SCIENTISTS have challenged the belief that vitamin D deficiency from lack of sunshine can cause increased heart disease and deaths in winter.
Research led by Emeritus Professor Hugh Tunstall-Pedoe from Dundee University suggests that vitamin D is unimportant in cardiovascular disease and winter deaths, whatever its role in other diseases.
Vitamin D was first linked with excess winter disease in 1981, the same year the Cardiovascular Epidemiology Unit in Ninewells Hospital in Dundee was launched to study causes of the excess heart disease in Scotland. Thousands of healthy men and women agreed to have risk factors measured, blood taken for testing, and their medical records followed, in the Scottish Heart Health Study.
Recently, their saved blood has been tested for vitamin D in Germany in a Medical Research Council and European Commission-funded international project.
Results were related to intervening illness and death. They show that while overall incidence of cardiovascular events did not vary seasonally, deaths from heart disease and from other causes did.
Vitamin D levels also varied, with highest levels seen in August and lowest in March – a two-to-one difference – but crucially this was several weeks after peak winter death rates, so changes in vitamin D were too late to be the cause.
People with lower vitamin D levels did have higher rates of cardiovascular disease, but low vitamin D levels were also associated with lifestyle and other risk factors.
When these were corrected for, vitamin D levels had a trivial or no additional effect.
People with low vitamin D levels did not have a greater increase in winter disease rates compared to others.
Prof Tunstall-Pedoe, who initiated and still leads the Scottish Heart Health Study, said: “This is a major study, in a population with two-to-one seasonal changes in vitamin D, and low levels overall.
“If vitamin D deficiency were a major cause of heart disease and death, we would have expected it to show up. But it did not. So our results seriously challenge its alleged role.
“We want others to explore seasonal change as we have done – a huge natural experiment which comes for free.
“All of this was made possible by the co-operation of healthy Scottish volunteers, by continuing access to their records, and by Scottish, United Kingdom, and European Commission funding at different times over many years.”
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, said: “We’ve known for many years that a low level of vitamin D is associated with an increased risk of cardiovascular disease, but it was not clear whether lack of vitamin D directly causes the increased risk or is a consequence of other factors.
“The long-term Scottish Heart Health Study, which the BHF helped to fund, has provided a series of valuable insights over the years and they have now shown that low vitamin D is result of other risk factors, rather than a cause of increased risk.
“The research team were able to use the large seasonal variation in vitamin D levels in the Scottish population in their study, which strongly supports the conclusions from other independent genetic studies.”
The findings have been published in the International Journal of Epidemiology.