I recently read that the incidence of ALS in the US was about 1/1000 (higher than I'd have thought). In Italy there were 33 cases among 24,000 soccer (football) players. That's about 50% higher than one would expect based on the US numbers (and the US numbers are lifelong, so the Italian soccer risk might well be 100% higher), but the article refers to a 4-5 fold risk increase.
Well, let's assume there really is a significant increase in risk in Italian soccer players compared to the general population. The commentary in the rest of the article is quite good:
The researchers suggested that the high risk might be linked to sports injuries, performance-enhancing drugs or exposure to environmental toxins such as fertilizers or herbicides used on football fields, as well as genetic factors.It's an interesting correlation, but I bet it's not a causal relationship. It does suggest some interesting research opportunities. Researchers will look at prevalence by socioeconomic class. Does ALS correlate with wealth or relative poverty? Is it related to the prevalence of some early infection? (I've always been interested in the relationship between MS and sunlight, presumably due to some modulation of the cutaneous immune system.)
But equally, it might be that people prone to ALS are drawn to sport, said Dr Ammar Al-Chalabi from London's Institute of Psychiatry.
'There could be some quality in their neuromuscular make-up that not only makes them good at sport, football particularly, but also makes them susceptible to ALS,' he said.
Dr Brian Dickie of the Motor Neurone Disease Association, said: 'We still don't know what causes this link, or whether it would be reflected in other groups of footballers and sportspeople.
'There is some anecdotal evidence of a link between high levels of physical exercise and an increased risk of developing motor neurone disease.
'However, much more research needs to be carried out before we can draw definite conclusions.'