What Causes Multiple Sclerosis in Females?

Multiple sclerosis (MS) affects women more often than men, but there is no single female-specific cause of the condition. MS develops when the immune system mistakenly attacks myelin, the protective covering around nerve fibres in the brain and spinal cord. Researchers still do not know exactly what starts this immune attack.

Current evidence suggests that MS develops through a combination of:

• Genetic susceptibility
• Epstein-Barr virus (EBV) infection
• Immune-system differences
• Hormonal and biological sex-related factors
• Low vitamin D or limited sunlight exposure
• Smoking
• Childhood or adolescent obesity

For a broader explanation of diagnosis and available therapies, see our main guide to Multiple Sclerosis (MS) Treatment.

Why Is Multiple Sclerosis More Common in Women?

Women are around two to three times more likely than men to develop MS. The exact reason is still being investigated. Researchers believe the difference may involve interactions between:

• Sex hormones such as estrogen
• Female and male immune responses
• Genetic factors
• Environmental exposures

Women are also more likely to develop several other autoimmune diseases, suggesting that biological differences in immune regulation may play an important role. However, estrogen or another female hormone has not been identified as the single cause of MS.

1. An Abnormal Immune Response

MS is an immune-mediated disease of the central nervous system. The immune system normally protects the body from infections. In MS, immune activity mistakenly targets structures in the brain, spinal cord and optic nerves. This damages:

• Myelin
• The cells that produce myelin
• Sometimes the underlying nerve fibres

The damaged areas can form MS lesions or plaques and interfere with messages travelling between the brain and the rest of the body. What causes the immune system to begin this attack is not fully understood.

2. Epstein-Barr Virus (EBV)

One of the strongest environmental links to MS is previous infection with Epstein-Barr virus. EBV is extremely common and is the virus that can cause infectious mononucleosis, sometimes called glandular fever. Research shows that people who have been infected with EBV have a higher risk of developing MS than people who have never been infected.

However, an important distinction is: EBV infection alone does not cause MS. Most adults have been infected with EBV, yet only a small proportion develop multiple sclerosis. The virus therefore appears to be one part of a larger combination of susceptibility factors.

3. Genetics and Family History

MS is not directly inherited in the same way as some single-gene disorders. However, genetics influence a person's susceptibility. Hundreds of genetic variations have been linked to MS risk, many involving regulation of the immune system. A woman may therefore have an increased risk if a close relative such as a:

• Parent
• Sibling
• Child

4. Female Hormones May Influence MS Risk

The fact that MS is considerably more common in women has led researchers to study estrogen, progesterone and other sex hormones. Hormones clearly interact with the immune system, and MS disease activity can change during hormonal stages such as pregnancy and the postpartum period.

This suggests that sex hormones may influence MS biology. But researchers have not established that:

• High estrogen causes MS
• Low estrogen causes MS
• Menstruation causes MS
• Pregnancy causes MS

5. Low Vitamin D and Limited Sunlight Exposure

Lower vitamin D levels and lower exposure to sunlight have been associated with a higher risk of developing MS. Vitamin D plays a role in immune regulation, which may partly explain this relationship. MS has also historically been more common in populations living farther from the equator, where sunlight exposure can be lower during parts of the year. However, vitamin D deficiency is considered a risk factor rather than a single cause. Taking vitamin D therefore cannot guarantee that MS will be prevented.

6. Smoking

Smoking is one of the clearer modifiable environmental risk factors associated with MS. People who smoke have a greater risk of developing MS than non-smokers. Smoking is also associated with a more aggressive disease course after MS develops. Avoiding or stopping smoking is therefore important both for general health and for people concerned about MS risk.

7. Childhood and Adolescent Obesity

Obesity during childhood or adolescence has also been associated with an increased risk of developing MS later in life. Researchers believe this relationship may involve:

• Chronic low-grade inflammation
• Hormonal factors
• Vitamin D metabolism
• Immune-system changes

Can MS Be Prevented?

There is currently no guaranteed way to prevent multiple sclerosis because many of its risk factors cannot be changed. For example, a person cannot alter:

• Their biological sex
• Their inherited genetic susceptibility
• Previous EBV infection

However, some potentially modifiable factors can be addressed. These include:

• Not smoking
• Maintaining a healthy body weight
• Avoiding vitamin D deficiency
• Maintaining overall cardiovascular and metabolic health

When Should a Woman Be Checked for MS?

Having MS risk factors alone usually does not mean that testing is required. Medical assessment becomes important when neurological symptoms develop, particularly symptoms such as:

• Vision loss or pain with eye movement
• Persistent numbness or tingling
• Weakness in an arm or leg
• Problems with balance or coordination
• Double vision
• Unexplained neurological symptoms lasting more than a brief period

The Bottom Line

There is no single known cause of multiple sclerosis in females. MS appears to develop when a person with genetic susceptibility encounters environmental and biological factors that contribute to an abnormal immune response against the central nervous system.

Women develop MS more frequently than men, and researchers believe hormones, genetics and differences in immune regulation may contribute to this female predominance. However, the precise explanation is still being studied. Important MS risk factors include previous Epstein-Barr virus infection, smoking, lower vitamin D or sunlight exposure and childhood or adolescent obesity.

Pregnancy, menstruation, stress and birth control pills should not be described as established causes of MS. The most accurate answer is that MS in women results from a complex interaction of genetics, immunity and environmental exposures rather than one identifiable event or lifestyle choice.