A large study from the US shows a strong link between being a funeral director and the risk of developing motorneurone disease or MND.
Known also as Lou Gehrig's disease after the famous baseballer who developed the condition, motorneurone disease affects about one person in fifty thousand each year and causes progressive loss of muscle strength as the motor nerves that control voluntary movement die away.
The majority of the cases of the disease occur sporadically without any family history of the condition, and doctors have concluded that the disease is probably in part caused by exposure to certain environmental factors.
One such factor might be the chemical formaldehyde, known more colloquially as embalming fluid.
Analysis of data from nearly 1.5 million people from the US National Longitudinal Mortality Study (NLMS), who shared details about their health and their occupations, showed a strong association between workers in the funeral trade and motorneurone disease.
Workers in this occupational sector had the highest inferred levels of formaldehyde exposure and were up to 4.76 times more likely to report suffering from motorneurone disease compared with unexposed individuals.
The link is biologically plausible since formaldehyde can be inhaled and also passes through the skin to penetrate the body's tissues.
It can interfere with mitochondria, which power our cells, and increase the production in the body of free radicals.
Motor neurones appear to be particularly vulnerable to this form of damage, which could culminate in motor neurone disease symptoms.
However, as Harvard T.H. Chan School of Public Health researcher Andrea Roberts and her colleagues point out in their paper, published this week in the Journal of Neurology, Neurosurgery and Psychology, the results need to be interpreted cautiously because they have detected only a potential association between formaldehyde exposure at work and MND.
They did not detect a dose-dependent relationship between formaldehyde exposure and motorneurone disease, which is regarded as crucial to prove a causal link.
The researchers also acknowledge that, alongside formaldehyde, "funeral directors are exposed to other chemicals used in embalming, as well as to viral, bacterial and prion pathogens," all of which might affect their disease risk...