Possible Causes of MS
Researchers have studied a variety of possible causes for multiple sclerosis (MS), and a combination of factors appears to be involved. A popular theory looks at commonly known slow-acting viruses (one that could remain dormant for many years), such as measles, herpes, human T-cell lymphoma, and Epstein-Barr. After being exposed to one of these viruses, some researchers theorize that MS may develop in genetically susceptible people.
In the absence of a solid understanding of the mechanisms that underlie MS, no specific genes for MS have been identified. Genes have some role in susceptibility to MS, but the exact mechanisms remain unclear.
The list of genes that have been investigated for MS susceptibility is long and continually expanding. Linkage studies show that the major histocompatibility complex (MHC), which is a cluster of genes on chromosome 6, has the strongest genetic effect in MS. Additionally, other genes make considerably weaker contributions to MS disease risk.
Some scientists are looking for a connection between MS and nutritional factors, including fat intake, as well as deficiencies in fish oil and Vitamin D. The idea that a diet rich in saturated fat may increase one’s risk of getting MS, as well as worsen his or her disease course, has been a popular theory for several decades. In addition to food and supplements, Vitamin D is also derived from sunlight. Reduced sunlight may be involved in the development of MS.
As noted earlier, populations living closer to the equator have a lower incidence of MS. A popular theory is that those living closer to the equator are exposed to more sunlight and therefore are less likely to experience a Vitamin D deficiency. Studies suggest that low levels of Vitamin D may increase one’s risk of MS. Conversely, the Nurses’ Health Studies (I & II) found that women who were taking 400 IU or more of Vitamin D daily had a lower risk of developing MS.
Salt is also under investigation as a possible factor in MS. One study showed that high dietary salt was found to increase autoimmune neuro-inflammation in animal models. A separate study revealed that higher salt consumption was associated with increased clinical and MRI disease activity in people with MS.
Parasites are a possible risk-reduction factor in the development of MS. The parasites in this instance are “helminths,” which refer to a wide variety of worms. Some are thought to be harmless, and many people had pinworms as children. Research has found that parasites can modulate the immune system and dampen its responses. People who have parasites are less likely to be diagnosed with MS, and as conditions in different countries become cleaner – with fewer parasites – the number of individuals being diagnosed is increasing in these parts of the world. Parasites are less common in the United States, which may contribute to the higher incidence of MS in this country. However, some types of worms could possibly make MS worse, so more research is needed.
In recent years, researchers have found that interactions between a person’s microbiome and his or her immune cells may contribute to the development and severity of many disease states – including MS. The microbiome refers to the many millions of bacteria that reside in a person’s body, with current research focusing mainly on the bacteria that live in the intestines (referred to as “gut microbiota”). Specifically, researchers have hypothesized that imbalances in the number or types of different strains of bacteria could potentially cause the immune system to be inappropriately activated to develop an autoimmune disease. Multiple groups are currently conducting research on the microbiome and its potential connection with MS.
Another factor linked to MS is cigarette smoking. One study shows that women who smoke are 1.6 times more likely to develop MS than women who are non-smokers. Individuals with MS who smoke also appear to be at a much greater risk of experiencing a more rapid progression of their disease.