The cause or causes of Multiple Sclerosis are still unknown. Although there are significant geographical variations in the distribution of people with MS throughout the world, a great deal of research has failed to uncover any tangible evidence that there are specific avoidable risk factors associated with the onset of the disease.

Genetic versus environmental causes

At present, the most likely cause appears to be a combination of genetic and environmental factors. Studies of identical twins, where one or both has MS, of fer what might be called the ‘purest’ way in which to investigate this theory: it appears that genetic factors contribute between
30 and 35% and environmental factors about 65–70% of the total contribution to the cause. These two figures suggest that further research needs to be undertaken on both issues. There does not seem to be one simple gene linked to MS, but we do know, for example, that first- degree blood relatives of someone with Multiple Sclerosis, such as children and siblings (brothers and sisters), are at slightly enhanced risk of the disease.
Amongst many other theories about the causes of MS, there has been a particular interest in the role of ‘heavy metals’. It is certainly true that an excess of some heavy metals in the body, such as lead, mercury and cadmium, may result in serious neurological damage. Lead in particular is a potential cause of neurological damage, although, with the reduction of lead in petrol, it is gradually being reduced in our environment, but at present there is no evidence that excess lead causes MS. Excess mercury can also produce neurological damage, and there has been much discussion about the possible problems with mercury-based dental fillings. However, a large proportion of the adult population will have had at least some mercury fillings in their lifetimes, and yet only a fraction of those people have MS. Dental amalgam does contain mercury which can erode over time and be absorbed into the bloodstream, but this is a very small contribution to the amount of mercury ingested by most people
(deep-sea fish is a much greater source). The exposure to dental amalgam is well within the safety limits currently recommended for mercury.

Infections and other diseases

Research has not shown Multiple Sclerosis to be caused by any particular bacterial or viral infection, but it is possible that the timing of a relapse may coincide with an infection. This could be due to a change in immune activity that allows the infection to gain hold: the bacterial infection can trigger an immune response, or both the relapse and the infection may occur in response to some unknown third factor.

Candida
At present there is a widespread interest, particularly amongst many involved in alternative or complementary medicine, in Candida albicans (thrush). Although candida can be associated with many symptoms, as well as having a low-level but debilitating ef fect on health, there is almost no formal evidence that it is associated with relapses of MS in itself. Candida infection may be a result rather than a cause of a weakened immune system, and it is also known to be more common as a side effect of some anti-inflammatory drugs used in Multiple Sclerosis. Of course, any infection with potentially problematic symptoms should be treated with antibiotics.

Herpes
Amongst viruses that have prompted scientific interest in relation to MS, the herpes virus HHV-6 is one of a number currently being researched. However, as with other viral candidates for a cause of MS, this line of enquiry is controversial and much debated.

Lyme disease
There is no evidence that this disease, which is spread by tics living on a range of animal species in the countryside, can cause MS, although its symptoms may mimic those of MS.

’Flu jabs and other injections
Many people with MS naturally look for a preceding event, such as a ‘flu jab, to explain why their symptoms have worsened, or why they have had an ‘attack’ or ‘relapse’. Research studies have failed to demonstrate any link between injections (vaccinations or inoculations) and any subsequent worsening of the MS.

Links between MS and other conditions including cancer
Many people with MS can point to symptoms and illnesses that seem to have preceded its onset. There is no clear definitive link that been established between the prior effects of diseases and the onset of MS. Of course as MS progresses, it may itself give rise, in ef fect, to other conditions, through a weakened immune system or just by ageing, for example.
There is no known link between cancer of any type and MS, but it is to be expected that some people with MS will develop cancer, but no more frequently than people who do not have MS.

Autoimmune diseases
There are strong similarities between some aspects of other autoimmune diseases, where the immune system is triggered into mistakenly attacking normal tissues in the body, and some aspects of MS. At present these conditions are still thought to be completely separate disease entities, although it is possible that there may be some very general biological processes underlying these conditions. These processes are the object of considerable recent research.

Stress
Fatigue, and possibly what we call ‘stress’, could have had some effect, not as a cause of MS, but perhaps as an exacerbating factor on some symptoms. However, although most people with MS probably feel that undue stress in their lives may bring on a relapse, scientifically this issue is still being argued over. Even so, many people have their own ideas about things that they feel are linked with their Multiple Sclerosis symptoms, and try to avoid them.

Accidents and injuries
Studies have compared accident and injury rates in people with MS who have had relapses and those who have not. Almost all have concluded that there is no significant dif ference in rates, or evidence to support trauma as causing or worsening MS. A more general issue is whether head injuries may have broken what is called the blood–brain barrier so that some parts of the CNS may themselves become contaminated and thus be damaged by the various blood products that are released. However, the relationship of any breach of the blood–brain barrier and the onset of MS is disputed.

Diet
There has also been extensive scientific research on MS and diet which may have some bearing in the medium and longer term on health in general.
There is substantial research indicating that what are called
‘unsaturated fatty acids’ – essential building blocks of the brain and nervous system – may be deficient in people with Multiple Sclerosis, which is why supplements containing these fatty acids have become popular. However, there is little evidence that taking supplements with the fatty acids has any major effect on MS. More generally, there is also little evidence that any particular diet has major effects on the course of MS, although some evidence suggests that a low-saturated fat diet may be beneficial as regards relapses.
Finally, there is little or no evidence that poor diet in itself causes MS – if this were so, the geographic and social distribution of MS would be very different.