Multiple sclerosis (MS) is a disease that does not affect men and women equally, with three times more women than men diagnosed in Australia and the number of women with MS on the rise in most countries around the world.
In fact, women are more commonly affected by autoimmune diseases generally. Women tend to develop MS earlier and have more frequent relapses, while men progress faster and often have worse outcomes. This has led many to wonder whether differences in men and women are partly responsible and particularly about the role of sex hormones in MS.
What are sex hormones and what do they do?
Hormones are messenger molecules made by the body that are released into the bloodstream. Sex hormones control and regulate the reproductive system and also give men and women their different characteristics. While all sex hormones are made by both men and women, particular sex hormones are associated with each gender and are found at much higher levels in either women or men.
The main sex hormones in women are oestrogen and progesterone. These hormones are mostly produced by the ovaries and control reproductive development in girls. Progesterone also as important roles in pregnancy and breastfeeding. Testosterone is the sex hormone that is higher in men and is produced in the testes. Testosterone is important for sperm production and muscle mass. While these are the main roles of the sex hormones, they do also have effects in other tissues such as the brain, spinal cord and immune system.
Sex hormones and risk of developing MS
The risk of developing MS changes throughout life and most people are diagnosed in early adulthood. When MS occurs in children, boys and girls are affected equally, but after puberty the number of females diagnosed sharply rises. After menopause, the risk of developing MS in men and women is again similar. This is thought to be linked to the relative levels of sex hormones in women changing through the course of their lives. Low levels of testosterone in men is linked to a higher risk of developing MS; men with MS have lower testosterone than men without MS but the reasons for this are unclear.
Pregnancy and MS
Pregnancy affects the course of MS in women with the disease. During pregnancy, particularly in the second and third trimester, there is a protective effect with relapse rates dropping up to 70% compared to levels before pregnancy. However, there is also an increased risk of having a relapse after the baby is born, with women three times more likely to have a relapse in the 3-6 months immediately after giving birth. This is thought to be due to changes in the mother’s immune system that occur during pregnancy that lead to increased immune tolerance (the immune system is ‘calmer’ and more tolerant of ‘foreign’ cells), to ensure that the mother’s immune system does not attack the growing foetus.
Big population studies have suggested that, on average, having children does seem to reduce the risk of developing MS but pregnancies do not seem to affect the overall accumulation of disability in women with MS. Many MS medications are not suitable for use during pregnancy, so it is important for women with MS who are considering or planning pregnancies to discuss their treatment options with their medical team.
Breastfeeding
It has been difficult to determine the effect of breastfeeding on MS, with some research showing it may be beneficial and reduces relapses in women with MS while others have shown it has no effect. This is complicated by the fact that women who have more severe MS are less likely to breastfeed or breastfeed for shorter periods. Disease modifying therapies are also not recommended while breastfeeding, meaning many will make the choice to forgo breastfeeding in order to restart treatment. Women who breastfeed their babies also have a lower risk of developing MS and babies who are breastfed have a lower risk of paediatric MS and adult MS later in life.
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