METHODS

Multiple sclerosis (MS) is a progressive, degenerative disorder that affects the brain, nerves and spinal cord. To date, little is known about its etiology. Women appear to be at higher risk of developing the disease than men (3:2 ratio).1 MS is rare in oriental populations,1-3 and its rate in whites is high-er than in blacks (2:1 ratio). In Canada, the age-adjusted incidence rate of MS is around 100 per 100,000.4 Geographical MS clus-ters have been reported in areas of low iodine concentration,5 high exposure to heavy metals,6 and high latitude.5,7,8 Besides genetics, lifestyle and local environmental factors play important roles in the etiology of the disease.9 Increased MS risk has been associated with a history of viral infections,10 higher socio-economic status11 and dietary habits.12 To study the possible role of socio-demographic characteristics, as well as lifestyle and medical history in the etiology of MS, we undertook a case-control stud