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The mystery of multiple sclerosis — and why Canadians have it most
Last Updated November 1, 2006
CBC News
Canadian women are more than three times more likely to get multiple sclerosis than men, according to a major study published in November 2006. Among those born in the 1930s, about two women contracted MS for every one man, at a ratio of 1.9 to 1. For those born in the 1980s, the incidence has grown to exceed 3.2 cases for every one case among men.
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Why the sudden increase in the neurodegenerative disease, which attacks the brain and spinal cord, and can lead to paralysis and sometimes blindness?
We don't know. We don't know what causes MS. We don't know what cures MS. The whys and wherefores of this mysterious disease have bedevilled scientists, health-care workers and victims for nearly 200 years.
Recent speculation about the cause has ranged from genetics to environment to vitamin deficiencies to even the birth control pill.
Canada has highest rate, especially in Prairies
One thing we know for sure about MS is that Canada has the highest incidence of the disease in the world — a whopping 240 cases among every 100,000 people, according to a study by a University of Calgary team published in the journal Multiple Sclerosis in 2005.
Health officials consider a country to have a "high" rate if they have more than 30 cases per 100,000.
The incidence among the provinces varies, from a high of 340 cases for every 100,000 people in the Prairies to a low of 180 cases per 100,000 in Quebec.
But overall, it works out about 1,000 Canadians being diagnosed each year with MS and more than 75,000 living with it. Those between ages 15 and 40 are most at risk. One out of every two Canadians know someone with MS.
Another thing we know about MS is that people who live closest to the equator have the lowest incidence.
However, that doesn't help explain why the disease is nearly absent among Canada's Inuit in the High Arctic and among indigenous people in North America and Australia, or why it is rarely found in Japan.
Study suggests MS is environment-based, preventable
The latest study on the rising incidence of women with MS was done by a team of researchers led by George Ebers, a professor of neurology at the University of Oxford. It appears in the November 2006 issue of the journal Lancet Neurology.
The higher incidence of MS among women may not be bad news, according to the researchers — because it may help to shed light on what causes the disease.
"What is going on here is something presumably that is preventable," said Ebers, who was the lead author of the study.
"We just need to find out what it is in the environment. Because it has to be in the environment: your genes don't change over two generations, three generations."
Others blame higher estrogen levels, less sunlight
There has also been speculation that because MS is generally more prevalent in colder climates far north of the equator and far south of the equator, it may be due to vitamin D deficiencies.
The body produces the vitamin in response to sunlight and so vitamin D levels fall off in colder countries and in winter because the sun's rays aren't intense enough.
Because of the rising incidence of MS among women and because it seems to have started in the 1960s, many others have speculated that the cause may be connected to higher levels of the hormone estrogen due to the introduction of the birth control pill.
But Ebers, who spent 22 years at the University of Western Ontario in London, Ont., before going to Oxford, rejects these factors as likely explanations.
"I think one of the things one thinks of here is either that it's going to be something in the environment or it is going to be an environmental interaction with genes."
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