Multiple sclerosis is up to 10 times more likely to strike people who live far from the equator, prompting scientists to theorize that a dearth of sun and/or vitamin D may trigger the disease. And for those with MS, flare-ups are far less common in summer than at the end of winter, suggesting that sunshine may help reduce the severity of the disease.
These striking geographical and seasonal patterns have inspired the world’s first clinical trial, launched in October, aimed at providing scientific proof of the theory. The randomized, placebo-controlled study is investigating whether daily doses of vitamin D—the sunshine vitamin—can prevent MS attacks or slow progression of the disease, which affects more than 2 million people worldwide.
In a scary trend, MS rates are rising, particularly in women, adding new urgency to the quest for better ways to prevent or treat the incurable disease. Here’s a look at the sunshine factor, the role of vitamin D, and new clues to the mystery of MS.
Rare in tropical countries, MS becomes more common as distance from the equator increases in either hemisphere. Northern Scotland and Canada have the world’s highest rates of MS, which is five times more likely to target Americans who live in northern states than those in southern states.
Other areas with high rates include northern Europe, from Iceland to Russia, New Zealand, and southern Australia, where rates of MS are ten times higher than in northern regions. However, there are some exceptions, such as the low rate of MS in Japan. Overall, MS attacks more frequently above 40 degrees latitude, with higher rates among Caucasians, particularly those of European ancestry.
This geographical pattern has led to the “latitude hypothesis,” the concept that where someone lives is a major risk factor for MS, due to differences in the amount of sunlight at various latitudes, especially during winter.
Higher latitudes experience what’s called “vitamin D winter,” in which the body is unable to produce any vitamin D, even on extremely sunny days. When the sun’s rays enter the atmosphere at a steep angle, the atmosphere blocks UVB rays. In latitudes above 40 degrees north, vitamin D winter lasts from November through early March, according to the Vitamin D Council.
A recent study published in Neurology found that people who get the most sun (as measured by skin damage from sun exposure) and those with the highest vitamin D levels were up to 60 percent less likely to develop MS. The researchers found that the effects of vitamin D levels and sun exposure acted independently from each other on disease risk, suggesting that both sunshine and getting ample vitamin D from dietary sources or a supplement are both protective.
However, there are some puzzling variables. For example, people born in a region with high rates of MS who move to a low-risk country before age 15 develop the disease at the reduced rates associated with their new location. Yet those who emigrate later in life don’t show any change in risk. However, their kids have reduced rates of the disease.
Another surprise from the research front: A recent analysis of studies involving more than 42,000 people in Canada, the UK, Denmark and Sweden reported that babies born in May are 13 percent more likely to develop MS later in life, while a November birthday reduced risk by 19 percent. The researchers theorize that the correlation between birth month and MS may be due to the mother’s sun exposure and vitamin D levels during pregnancy.
These findings suggest that childhood environment plays a key role in triggering the disease, but the reason is unknown. However, researchers have long suspected that viral infections may be a contributing factor. A 2011 study linked MS risk to a combination of living in an area with little sunlight and past infection with mononucleosis, which is caused by the Epstein-Barr virus.
The researchers examined records from all hospital admissions in England between spring, 1998 to spring, 2005, and concluded that these two factors explained 72 percent of regional variations in MS rates in that country. In earlier studies, the researchers found that varying amounts of sun can influence risk even within small geographical regions. In Scotland, for example, MS rates are higher in Glasgow than in the sunnier city of Dundee.
‘“Vitamin D is potentially a cheap and safe therapy,” said Helmut Butzkueven, the chief investigator of the world-first clinical trial of the sunshine vitamin as a new weapon against MS. Earlier research suggests that in northern latitudes, MS rates are lower in countries where people eat a lot of oily fish, which is high in vitamin D. Other natural sources include cheese, egg yolks, and certain mushrooms, along with vitamin D-fortified orange juice.
“There is lots of circumstantial evidence that links low Vitamin D levels to [MS] disease causation and disease activity. Through this clinical trial, we aim to obtain solid evidence, and work out what doses we should recommend,” Butzkueven remarked in a statement.
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