We’re used to the idea that some aspects of our lives might put us at higher risk for certain diseases. We know, for example, that our diet and exercise habits may make us susceptible to some health problems. But in the case of multiple sclerosis, the place we live could raise our chances of developing the disorder and increase the risk of more severe symptoms.
Multiple Sclerosis and Latitude
Researchers have noted that multiple sclerosis (MS) seems more prevalent in the higher latitudes in the northern hemisphere and the lower latitudes in the southern hemisphere. In the past decade, research has confirmed that people living at higher latitudes in both hemispheres are at a statistically significant increased risk for the disorder.
Recent research suggests it’s not just the frequency of MS that increases the farther you go from the Equator. For example, a 2016 study found that the average age of MS onset for people living at latitudes above 50 degrees was two years younger than for those living below 19 degrees. In addition, a study published this year in the journal Neurology found that people living above 40 degrees latitude were likely to experience more severe MS and a faster decline in neurological function than those living at lower latitudes.
The latter study could cause concern since its 40-degree boundary is a relatively low latitude. In the United States, much of the population, including residents of New York, Boston, Chicago, Minneapolis, Portland, and Seattle, reside above that line.
Sunlight and Vitamin D
The link between latitude and MS is definite, but what’s behind it? The genetics of local populations and cultural differences might play a role, but a common factor among high-latitude residents is exposure to sunlight. At high latitudes, low sun angles, and short days during the winter limit the time locals are subject to exposure to the sun’s rays, which is a problem.
Sunlight, particularly its ultraviolet rays, is a vital source of nutrients essential to our health. For example, our bodies can create vitamin D3 when our skin absorbs ultraviolet B radiation, a component of sunlight. Without sunlight or some other source of vitamin D, we’re at risk of a vitamin D deficiency. That deficiency could lead to disorders ranging from osteoporosis to cancer and heart disease.
Scientists suspect a lack of vitamin D might also increase our risk of MS. Apart from the question of sunlight exposure, multiple studies have shown that people with higher vitamin D levels have a lower risk of developing MS. In addition, some studies have suggested that people with more vitamin D in their bloodstream may have less severe symptoms if they do develop the disorder.