In MS, immune reactions caused by a person’s own immune cells result in damage to the nervous system, but what repeatedly triggers these reactions is not known. While many different causes and theories have been entertained and studied so far, we have not yet found a single cause or a risk factor. Instead, we view MS as a perfect storm in which many environmental factors affect people who are genetically prone to autoimmune diseases. It is also clear that because MS behaves differently from patient to patient, triggering and perpetuating factors leading to the disease might also be different from one person to another.
Multiple sclerosis is not a typical genetic disease with strong heritable patterns. Only 20 percent of people affected by MS have a positive family history. The risk of developing MS in the general population is about 0.13 percent. This risk increases to 2 to 3 percent in first-degree relatives, and it is slightly higher for siblings than for parents and children. Identical twins have the risk rate of 30 percent.
While genetic studies failed to identify one candidate gene responsible for MS, the studies did identify multiple small variations in the genome that could, after interactions with environment and each other, predispose people to develop MS. It is not surprising that some of these variations were previously linked to other autoimmune diseases, such as thyroid disease.
As the genetic research in MS continues, we expect to find more variations that could explain the risk of developing MS as well as the differing severities of the disease and responses to treatments. To this day, however, there is no genetic test available to predict the risk of MS.
Multiple environmental factors have been studied as causes of MS, but similarly to genetic factors, we have not identified a single factor responsible for triggering the autoimmune cascade. Among many potential causative factors, the following have shown the strongest association with the risk of developing MS:
Vitamin D and Exposure to UV Light
Vitamin D, exposure to sunlight and ultraviolet radiation (UVR) play an important role in the function and regulation of the immune system. Multiple research studies showed strong association between high exposure to sunlight and vitamin D levels in adolescence with the decreased risk of developing MS.
The increased risk of MS in smokers was first reported in the 1960s, and recent research has made this point more valid. To date, several studies have showed the detrimental effects of smoking on the risk of MS and also showed that both the amount of cigarettes and duration of smoking affect this risk independently. Unlike other environmental factors, smoking at any age increases the risk, and this negative effect continues for approximately a decade after quitting.
Research has not been consistent regarding the connection between second-hand smoke and the development of MS, such as the onset of MS in children with parents who smoke. Also, there has not been conclusive research regarding the connection between children with MS and mothers who smoked during pregnancy.
Epstein-Barr Virus Infection
The role of Epstein-Barr virus (EBV) in the risk of MS development has been debated by scientists for a long time. The frequent presence of EBV in MS patients is a known fact, but whether this means that EBV causes MS is unknown.
The EBV is present in more than 90 percent of the world’s population. The EBV can either cause a silent infection without any symptoms, usually in childhood, or an actual infectious disease called infectious mononucleosis (IM), happening usually later in adolescence or adulthood. We do know that the IM infection does increase the risk of developing MS and that people who do not show presence of EBV have extremely low risk of MS. However, we don’t know is if the EBV is directly causes MS or whether some other factor makes people susceptible to both MS and EBV infection.
Adolescent Obesity and Shift Work
Studies have shown that both childhood and adolescent obesity (but not adult obesity) has led to an increased risk of developing MS. The mechanisms behind the negative effect of obesity might involve fat-related long-term inflammation as well as lower vitamin D levels that were found in obese people.
Shift work at a young age, which leads to lack of sleep and disruptions of normal sleep cycles, has also been suggested as a factor in increasing the risk of MS later in life. The mechanism here involves disturbance in the secretion of the natural sleep hormone melatonin and increased inflammatory processes in the body.
Alcohol and Coffee
The impact of alcohol and coffee on MS risk has been investigated in a few studies, and results suggest possible protective effects from both. The protective effect also depended on the amount consumed. While the results are inconclusive and require further studies, no recommendation to change alcohol or coffee habits in order to decrease a risk of MS is given at this time.