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Is the incidence of multiple sclerosis increasing?

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It seems almost everyone I've spoken with in the past few years has a family member or friend with a diagnosis of multiple sclerosis. What's going on here? Is the incidence increasing? Is it being recognized with greater accuracy due to improved testing? Or is it one of those catch-all diagnoses for unexplained problems of the central nervous system? —HarryLlama

Yup, multiple sclerosis seems to be increasing, possibly a lot. A rare disease once upon a time, MS is now the most common neurological disorder affecting young adults of northern European descent. In the United States alone, an estimated 266,000 to 400,000 people currently have it.

MS is a chronic, incurable condition that can't be prevented or effectively treated. The body's own white blood cells strip the protective sheathing (myelin) off nerve cells in the brain and spinal cord, leading to poor nerve function and a wide range of debilitating symptoms—numbness or tingling, dizziness, weakness, spasms, loss of coordination, problems with vision and urination. MS won't kill you directly, but it can take five to 10 years off your life.

The causes of MS remain mysterious, although some trends are evident among those who get it. There's a definite genetic tendency toward the disease, although twin studies show environmental factors also play a part. Cigarette smoking is implicated not only for prevalence but severity of symptoms.

It's long been thought there was a link between latitude and MS—people living above 42 degrees north were more likely to get the disease, and the further north you went, the greater the risk. A 2011 study in Sweden concluded the prevalence of MS increased by 1.5 percent for men and 1 percent for women for each degree of latitude further north. The same effect has been found in Japan and an equivalent southern-hemisphere effect in New Zealand, where the risk increases as you head south.

Other researchers downplay the latitude gradient, saying the real problem is vitamin D deficiency. Latitude figures in this because the greater your distance from the equator, the lower your exposure to ultraviolet radiation, specifically the shorter-wavelength UV-B, and the less vitamin D you produce. Some claim to see a link between spring/early-summer birthdays and MS, which could be tied to mothers' lower UV-B exposure during pregnancy.

Research in the U.S. indicates an east-west gradient for MS prevalence, possibly related to the spread of Scandinavian immigrants across the country. Meanwhile, back in Norway, there seems to be reduced risk in the northernmost regions, possibly due to greater local consumption of oily fish. To further confuse matters, there's apparently little relationship between MS and vitamin D in food, although vitamin D supplements may have a protective effect.

MS is mostly a problem for those of northern European ancestry—it's rare in Asia, Africa and the Middle East. That's not just because nonwhites tend to live closer to the equator. In Australia and New Zealand, for example, MS is far more common among those of British background than Aborigines and Maori.

Back to the fundamental question: Is MS becoming more common? Sure looks that way. A 35-year Australian study found the MS prevalence (total-cases) rate tripled and the incidence (new-cases) rate doubled between the early 1960s and the mid-1990s. A study of one county in Norway found incidence went up by a factor of 3.3 over 50 years, with smaller increases in other counties.

Women have borne the brunt of the jump in MS. Between 1950 and 2000 the ratio of women to men with the disease increased by about 1.4 percent per year. Nowadays, it's estimated that women are 50 to 300 percent more likely to be diagnosed with MS than men.

Why? Nobody knows. One possibility is women are simply more likely to seek help for MS-like symptoms. Other hypotheses include more obesity, increased use of oral contraceptives and hormone-replacement therapy, and a trend toward later childbirth. Then again, research shows MS was increasing in women even in the pre-pill days, and for that matter, before any of these other trends had emerged.

Improved diagnosis undoubtedly does explain some of the increase. One study found MS rates in parts of Finland were fairly stable from 1979 to 1993, then more than doubled between 1994 and 1998—a jump the investigators attributed to greater use of magnetic resonance imaging to aid in diagnosis.

Another explanation for the increase is that people with MS are living longer. Still, factoring all that out, the consensus seems to be that there's been a real increase in MS in the past 50 years, possibly due to some unknown environmental cause.

I don't mean to be alarmist. A disease that even in hotspots afflicts three people in a thousand doesn't qualify as the next Ebola. The fact remains that if you're a woman of northern European extraction and someone in your family has MS, there's a growing chance you'll get it, too.

Send questions to Cecil via StraightDope.com or write him c/o Chicago Reader, 350 N. Orleans, Chicago 60654.

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