A recent study found that the one in six adolescent girls who are overweight are at increased risk for multiple sclerosis. Multiple sclerosis in obese teenage girls is also more dangerous, and the girls have a higher risk of a multiple sclerosis precursor called clinically isolated syndrome, in which the deterioration of myelin characteristic of MS causes one or more neurological effects for a period of 24 hours.
The researchers looked at the body mass index data for MS patients who were diagnosed under 18 and compared that with data for healthy children. They used these figures to sort the subjects into weight categories: normal weight, overweight, moderately obese, and extremely obese. More than half the children with the condition were overweight or obese, while only slightly over a third of those without it were, but the effect was only seen in girls. Extremely obese girls had four times the risk of MS as normal weight girls.
Researchers speculate that obesity, which is often associated with slight inflammation, may contribute to myelin deterioration. Multiple sclerosis is an autoimmune disease in which the immune system attacks the protein myelin that covers the nerves. Menstrual hormones also contribute to inflammation, and female bodies generally show the effects of obesity earlier than male. These factors may account for only girls showing the association; MS in general occurs more frequently in women than in men. Obesity, though a risk factor for a number of conditions, had not previously been considered in connection with MS.
There is some evidence of a genetic predisposition to MS, but the illness still only occurs in the presence of certain triggering factors, of which obesity may be one. Established risk factors, aside from being female, include infections such as the Epstein-Barr virus, other autoimmune diseases such as type 1 diabetes and thyroid disease, and living far from the equator before puberty—it’s not clear why the geographical factor has an effect, nor why it’s only in childhood, but it supports the “hygiene hypothesis” often cited as a possible explanation of autoimmune diseases.