Epidemiology: a predominantly female disease

Generally speaking, autoimmune diseases are more common in women than in men. There are certainly links between the endocrine system, and therefore hormone production, and the immune system.

It is well established that use of the contraceptive pill is not a factor of susceptibility to developing or in aggravating the disease. On the other hand, progestational hormones, synthesised in high doses during pregnancy, have a protective effect on attacks of the disease. These decrease during pregnancy, from quarter to quarter, but may be more frequent in the 3 months following childbirth. It is estimated that 20% of women with MS are likely to have a relapse in the 3 months following childbirth. Other epidemiological studies have shown that pregnancy has a protective effect on the course of the disease, whether the pregnancies occurred before or after the onset thereof. Pregnancy is characterised by a state of relative immunosuppression, in order to tolerate the little "foreigner" that is the foetus. This state of tolerance can therefore be positive for the course of MS in the short and even long-term.

The prevalence of the disease has increased in Europe by roughly 30% over the past ten years. In France, it is 2.3 times higher in women than in men, with a peak for both sexes between 55 and 59 years of age. If we take into account the epidemiological data observed in the departments of northern France bordering Belgium, figures of 225 to 250 per 100,000 inhabitants are observed (2021 figures published in 2024).

The exact reasons for this disproportionate increase in women are not known, but higher female smoking and later pregnancies certainly contribute. However, the incidence of the disease stabilised in France between 2012 and 2021 and stands at around 6.98 new cases per 100,000 inhabitants per year. The rise in prevalence is therefore essentially attributable to a marked improvement in life expectancy, whose median is 74.7 years according to a 2017 Norwegian study, compared with 81.8 years in the general population.

The increase in the number of people with MS is seen much more inwomen than in men. As a result, the female/male ratio is increasing, from 1.8:1 in the past to 3:1 today. The incidence of the disease, i.e. the number of new cases diagnosed each year, is also on the rise, having doubled in women between 1950 and 2009, while increasing by only 24% in men over the same period, according to a Danish study.

With a population of 11.5 million, the number of people with MS in Belgium is estimated at around 25,000, with 800 new cases each year.