For unknown reasons, the nerve disease multiple sclerosis (MS) has been taking an increasingly greater toll in women than in men.
In MS, the body’s own immune system repeatedly attacks the protective covering of nerve cells in the brain and spinal cord, causing worsening problems with weakness, muscle co-ordination, vision and other functions. Researchers aren’t sure what triggers these attacks.
Gary Cutter of the University of Alabama at Birmingham recently reported that the ratio of female to male MS patients has increased from about two to one in 1940 to about four to one in 2000.
He and his colleagues used data from a North American registry to track the sex ratio of more than 30,000 MS patients over 60 years. The odds of an MS patient being female increased by nearly five per cent per year, or almost 50 per cent per decade. The increases were more prominent in younger groups.
The results echo those of a 2006 study that identified similar trends in Canada. Cutter says the value of such research is that it may provide clues about the causes of MS. “Maybe through the idea that there’s something going on that’s causing something to occur more frequently in females, maybe we can get somebody with some bright ideas to chase down what that might be.”
So far, however, researchers don’t have any firm explanations for the trend. Cutter says he is pondering possibilities as diverse as changing obesity rates, and the use of cosmetic products that may affect the body’s levels of vitamin D, a shortage of which could be a factor in the development of MS.
An increase in smoking among women did not explain the increasing proportion of female MS patients. Nor did the trend toward delayed childbearing. “We do know that women would be more exposed to hormones in the sense that menarche is becoming earlier and women are often delaying pregnancy a little bit more, they’re taking birth control pills more frequently now. But … the evidence for (the female hormone) estrogen is that it might actually be protective.”