The study, published in Neurology, included Australians living from latitudes 27°S to 43°S. These latitudes receive about the same amount of annual sunlight as a region extending from Tampa, Florida, to Concord, New Hampshire, and from Baja California, Mexico, to Eugene, Oregon.
Study participants were 216 people who had recently been found to have the type of nerve damage seen in multiple sclerosis, known as demyelination. They were compared with 395 otherwise similar people without demyelination. All participants answered questions about their past, recent, and total leisure-time sun exposure. They also had their skin examined and rated for sun damage, and blood levels of vitamin D (25-hydroxy) measured.
Similar to previous studies, this one found that more people with the demyelination type of nerve damage lived in the far southern latitudes than the middle latitudes. Moreover:
"Our findings suggest that sun exposure and vitamin D status are independently important factors in the development of multiple sclerosis," said study lead author Associate Professor Robyn Lucas of the Australian National University. "If this is true, vitamin D supplementation alone may be less effective as a preventive strategy than previously thought."
While many people may be out enjoying the summer sun while they have it, it’s worth a discussion with your doctor on the relative risks of premature aging and skin cancer compared with multiple sclerosis risks. In any case, if you live in a place where summers are short, you might want to take extra steps in the hope of preventing nerve damage: