The presence of a bird in your house could multiply your chances of developing multiple sclerosis by a factor of two or more. On the other hand, if your pet is a cat, you could cut your risk by half. Astonishing, but true, according to the findings of a recently concluded epidemiological study by Dr. Parviz Ghadirian, professor of Nutrition at the Université de Montréal and director of the university hospital (CHUM) epidemiology unit. The study compared the living habits of 200 Montrealers suffering from MS with those of a control group that did not have the disease. "We don't know precisely what may be the factor with birds, but the results suggest a virus they carry may act as a vector for multiple sclerosis," says Dr. Ghadirian. Other epidemiological studies have also shown a similar link.

As for cutting your risk of getting MS with a cat, the UdeM researcher maintains the effect could be of a psychological nature, perhaps a form of zootherapy: "We don't have an explanation there either, but it is known that the presence of an animal companion, like a cat or dog, improves the quality of life and their owners have less arthritis and other chronic complaints, and suffer less from hypertension."

Professor Ghadirian's research also brings to light a difference between men and women: the beneficial effect of having a cat is more pronounced among men (70% less risk versus 40% less for women). But the negative effect of keeping birds is significant only among women (2.5 times higher). "If a virus is the cause with birds, the difference between men and women could be explained by the fact that women are in contact with the animal longer if they stay at home or because they're the ones that change its litter," the researcher says.

The Ghadirian study also revealed another previously unknown factor. Smoking 20 or more cigarettes a day doubles the risk of contracting MS compared to the risks to a non-smoker. "Smoking appeared as the highest environmental risk, and this is the first time the link has been established in a control-group study," he says.

Multiple sclerosis is a degeneration of the central nervous system (the brain and spinal cord) characterized by scattered hard (sclerotic) areas of scarring where myelin, the fatty layer of insulation around neurons, has been destroyed. In an earlier study, Dr. Ghadirian found that a high consumption of animal fats doubles the risk of MS, while consumption of edible fibers and cereals reduces risk by about 40%. "Which means it's easy to reduce the risk of developing this disease," the epidemiologist says. "Stop smoking and develop good eating habits."

Researcher: Parviz Ghadirian
Phone: (514) 890-8000
Funding: Association de la sclérose en plaques de Montréal Est