Multiple sclerosis is an inflammatory disease associated with a loss of myelin, the protective layer that surrounds the cells of the nervous system. Although the origin of this disease remains mysterious, recent observations suggest that obesity and vitamin D deficiency could promote its development.
In the brain and spinal cord, the nerves are surrounded by a protective sheath called myelin, which acts as an electrical insulator to allow the rapid transmission of nerve impulses (up to approximately 400 km/h). For a reason still unknown, the immune system can in some cases attack this myelin and the resulting inflammation causes the destruction of this protective layer.
The loss of myelin then causes certain portions of the nerves to become “bare”, which slows the speed at which nerve impulses travel and leads to problems with feeling, movement or mental processes. Since these lesions (sclerosis) where myelin is absent appear as hardened scars resembling “plaques”, this disease has been given the name multiple sclerosis (MS) or, in more specialized language, multilocular sclerosis.
The first symptoms of the disease usually occur between the ages of 15 and 40 and can vary depending on which nerves are affected. The most common are decreased vision, weakness of one or more limbs, balance disorders and tingling or abnormal sensations in the body or face. The subsequent course of the disease is highly variable, but often occurs in the form of very abrupt “flares” where neurological symptoms can worsen quite quickly, followed by stabilization and more or less complete recovery. When these flare-ups occur at regular intervals, neurological damage can accumulate over time and lead to a gradual decline in abilities.
Multiple sclerosis affects women more
The causative factors of MS remain poorly understood. We know that people of Caucasian origin who live in northern regions are more at risk of being affected, especially women (three women for every man). There therefore seems to be a genetic predisposition to MS, but this predisposition cannot, however, explain on its own the appearance of this disease: studies indeed indicate that external factors must absolutely intervene to trigger the abnormal immune reaction.
Prevention of multiple sclerosis
Studies indicate that vitamin D insufficiency could be one of these factors. For example, the incidence of MS is higher in people living in regions farther from the equator (and therefore less sunny) and several observations suggest that a reduced intake of vitamin D as well as blood levels of this vitamin in below normal were associated with an increased risk of MS. Research also indicates that people who show the first symptoms of the disease are much more at risk of seeing their condition deteriorate if they are deficient in vitamin D (less than 50 nmol/L).
Another study suggests that maintaining a normal body weight may also reduce the risk of developing MS. By calculating the body mass index (BMI) of 210 patients with the disease, researchers have in fact observed that people who are obese at the age of 20 (BMI > 30) have twice the risk of SEP. This effect would be caused by an increase in the hormone leptin, which activates several phenomena involved in inflammatory processes.
Protective factors for multiple sclerosis
MS is another example that you can be born with genes that predispose you to a disease, but the development of that disease is still strongly influenced by a host of outside factors. In this sense, the maintenance of a healthy weight as well as a normal blood concentration of vitamin D, for example by exposing the skin to the sun for 10-15 minutes a day in summer or by taking supplements of 1000 IU in winter, could represent simple and concrete ways to reduce the risk of being affected by multiple sclerosis.
Munger KL et al. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA 296: 2832-8.
Ascherio A et al. Vitamin D as an early predictor of multiple sclerosis activity and progression. JAMA Neurol. 71: 306-14.
Correale J et al. Body Mass Index and Multiple Sclerosis Risk. The Role of Leptin. 66th Annual Meeting American Academy of Neurology (AAN), Philadelphia,
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