An abundance of vitamin D seems to help prevent multiple sclerosis, according to a study in more than seven million people that offers some of the strongest evidence yet of the power of the “sunshine vitamin” against MS.
The research found that white members of the US military with the highest blood levels of vitamin D were 62% less likely to develop multiple sclerosis than people with low levels.
There was no such connection in black or Hispanic people, possibly because there were so few in the group studied. Also, the body makes vitamin D from sunlight, and the pigmented skin of blacks and other dark-skinned ethnic groups does not absorb sunlight as easily as pale skin.
The new research echoes findings in smaller studies that examined why the nerve-damaging disease historically has been more common in people who live in regions further from the Equator where there is less intense year-round sunlight.
“This is the first large prospective study where blood levels are measured in young adults and compared to their future risk. It’s definitely different and much stronger evidence,” said Dr Alberto Ascherio, the senior author and an associate professor of nutrition at Harvard’s School of Public Health.
The study appears in today’s Journal of the American Medical Association.
“If confirmed, this finding suggests that many cases of MS could be prevented by increasing vitamin D levels,” Dr Ascherio said.
However, he said the findings do not prove that a lack of vitamin D can cause MS, so it is too preliminary to recommend that people take vitamin D pills to avoid the disease.
Vitamin D also is found in fortified milk and oily fish, but it is hard to get enough just from diet. Sunlight is the biggest source of vitamin D, which is needed for strong bones. Other studies have linked high levels of vitamin D in the blood to lower risks of a variety of cancers.
The MS researchers worked with the Army and Navy in analysing blood samples of military personnel stored by the US Department of Defence.
Military databases showed that 257 service men and women were diagnosed with MS between 1992 and 2004. The increased MS risk was especially strong in people who were younger than 20 when they entered the study. The researchers said that finding suggested that vitamin D exposure before adulthood could be particularly important.
Using blood samples to measure vitamin D levels “tends to nail it down in a much more reliable way” than studies that have relied on people’s memories of vitamin D exposure, said Dr Nicholas LaRocca of the National Multiple Sclerosis Society.
MS is among the most common nerve disorders affecting young adults, mostly women. About 350,000 people in the US and two million worldwide have MS, a chronic auto-immune disease in which the body attacks the fatty insulation that surrounds nerve fibres.
Dr Ascherio said there was some evidence that its incidence was increasing in sunny regions, possibly because people are avoiding the sun or using sunscreen to protect against skin cancer.
Some doctors think those practices have also contributed to vitamin D deficiencies in adolescents and young adults.
“There’s no question that vitamin D deficiency is an epidemic in the US,” said Dr William Finn, a vitamin D expert at the University of North Carolina at Chapel Hill. The MS study “is just one more reason to pay attention to it”.
MS symptoms vary but can be disabling and can include tingling pain in the arms and legs, fatigue and vision problems.
Doctors believe it is genetic and perhaps triggered in susceptible people by environmental causes, including possibly some viruses. Vitamin D deficiency could be another trigger.
It is unclear how lack of vitamin D might contribute. In mouse experiments, the vitamin stimulated production of chemicals that fight an MS-like disease.