Pollutants and brain disease
'Pollutants cause huge rise in brain diseases' declared the UK Observer, headlining a report from researchers at the University of Southampton Medical School published in the journal Public Health. The study compared rates for two categories of deaths (including dementia and Parkinson's disease) across 10 countries, contrasting figures from the period 1979 to 1981 with 1995 to 1997.
They found a big increase in most countries across both categories. For example, there were around 3,000 deaths from these diseases per year in the 1979-81 period in England and Wales - which rose to 10,000 deaths per year in the 1995-97 period. Given that genetic changes could not have occurred this quickly, the researchers conclude that there must be an environmental explanation.
'This has really scared me', said Professor Colin Pritchard, the lead author of the study. 'These are nasty diseases: people are getting more of them and they are starting earlier. We have to look at the environment and ask ourselves what we are doing.'
This study does not examine any pollutant or even any single disease. It merely examines recorded deaths for these groups of diseases over two periods to look for trends, and then speculates about what might be causing these trends. The 'tentative explanation' the authors put forward is just that - tentative. It certainly does not warrant banner headlines.
The first thing to be pointed out is just how rare these diseases are. Consider the figures for England and Wales: in 1979-81, there were 85 deaths per million of the population from these diseases - or 0.018 per cent of the population. In 1995-97, this had increased to 0.034 per cent. As a percentage of deaths from all causes in women, the rise was from 1.67 per cent of all deaths, to 3.54 per cent - more than double what it was before, but still a small number given that this includes dozens of different diseases. (The equivalent figures for men are lower: 1.23 per cent and 2.61 per cent.)
Secondly, these diseases are overwhelmingly diseases of old age. In the 1979-81 period, in England and Wales, someone over the age of 75 was 13 times more likely to die from one of these conditions than someone in the 55-64 age group. In 1995-97, the over-75s were 24 times more likely to die than the 55-64 year-olds. The incidence of these diseases below the age of 55 is even smaller.
Thirdly, the authors are quite wrong to assume that environmental factors are key to the increase. The most important factor in the rising numbers of people dying from these conditions is that the population is getting older. To that extent, there is a real, but manageable problem of coping with an increasing number of people living with these conditions in the future.
But the next most important factor is surely one of labelling. The figures for Italy are quite dramatic in this regard. In 1979, in the 75+ age group, the rate of death from dementia-like illness was 45 per million. In 1995-97, the rate was 1,211 per million for the same age group. We can either conclude that there has been a marked change in diagnosis and death certificate practice in Italy - or that someone has been going round attacking Italian pensioners with a special dementia gun. The idea that any factor in the Italian environment could engineer a real 27-fold increase in a particular cause of death is laughable.
The cross-national comparisons are almost as bizarre. In the 1990s in Italy, 1.2 per cent of deaths were due to these dementia-like illnesses. In Canada, the figure was 2.6 per cent. Are people really more than twice as likely to die from these causes in Canada? Again, it is much more likely that differences in labelling and healthcare practice are to blame.
There may be changes going on in the death rates from these diseases, but the methods used in this report are simply incapable of detecting them - and a panicky search for some external cause is unnecessary.
Changing patterns of adult (45-74 years) neurological deaths in the major Western world countries 1979-1997,
Public Health, June 2004
Don't panic