Risk Factors

Factors Associated with a Higher Risk for Multiple Sclerosis

Cow's Milk During Early Infancy. Breast milk contains factors that may help regulate the immune response, and there is some evidence that infants fed only on cow's milk may have a higher risk for either diabetes type 1 (another type of autoimmune disease) or multiple sclerosis later in life. Studies on national differences in diabetes suggest that the risk may vary with different milk proteins, suggesting that not all cow's milk is the same and some proteins carry higher risks than others.

Factors Associated with Lower Risk for Multiple Sclerosis

The Hygiene Theory: Early Infections as Protection Against Allergies and Autoimmune Diseases. Over the past decades, there has been a dramatic increase in asthma, allergies, and autoimmune diseases, such as multiple sclerosis, Crohn's disease, and type 1 diabetes. One theory blames this rise on the reductions in childhood infections that have occurred with modern hygiene and antibiotic use. Studies supporting this have observed a higher incidence of allergies and autoimmune diseases, including MS, among populations with good hygiene and in animals that have been raised in a germ-free environment. The basic theory rests on the idea that early infections stimulate production of specific immune factors that protect against allergies and autoimmune diseases. The exact mechanisms of these effects are as yet unknown. Of note, there is no evidence indicating either a positive or a negative role of vaccinations in the development of autoimmune or allergic diseases.

Exposure to Sunlight. In a 2003 study, higher exposure to sunlight during childhood and early adolescence was associated with a lower risk for MS, perhaps because UV radiation produces higher levels of vitamin D, which has been associated with protection against MS. The effect of sunlight during winter seemed to be more protective than summer light. Unfortunately, higher exposure to sunlight also coincides with a higher risk for skin cancer, which is far more common than MS.

Estrogen and Oral Contraceptives. Higher estrogen levels may temporarily lower the risk of developing multiple sclerosis. Studies indicate that oral contraceptives (which contain estrogen) and pregnancy delay the onset of multiple sclerosis. The risk for a first clinical attack increases, however, in the 6 months after a woman gives birth.