Now it’s suggested that a lack of exposure to strong sunlight may be giving people multiple sclerosis (MS).
Suspicions were aroused when it was found that ethnic minority people form countries close to the equator had a far greater prevalence of the disease in London than in their own countries.
The chances of contracting MS vary greatly by ethnicity anyway. There are about 100,000 MS sufferers in the UK with white people most at risk while people from sub-Saharan Africa and south Asia suffer least.
Based on a study of health records of almost a million people in east London, the gap narrows significantly in populations living there. Asian and black people had several times the risk of those still living in their home countries.
They found that the prevalence of MS among white people was 180 per 100,000 and 74 and 29 for black and south Asian people respectively. It also affects twice as many women as men. The WHO records show a prevalence of only 0.3 per 100,000 in Africa and 2.8 in south Asia. Dramatically different figures.
So as well as having a genetic component there are probably also environmental and lifestyle factors coming into play.
Klaus Schmierer from Queen Mary University who carried out the research said that current figures for ethnic minorities were almost half those for people with white skin. “Within one generation of being here the likelihood of getting MS has multiplied. This strongly suggests an environmental (rather than genetic) factor”
Some experts however wonder whether or not the gap is due to poorer diagnosis and/or recording of the disease in Africa and Asia. The MS Society welcomed the research but said it was too early to draw firm conclusions from it.
This is how we make progress though, through little steps.