Eat Dirt, Channel 4, 20 June at 9 pm
E at Dirt, Channel 4's recent documentary on asthma, tackled the science behind the rise in this disease in the West. The crucial cause, it suggested, is dirt—or rather the lack of it in our daily lives.
Starting with a historical perspective, the programme linked the dramatic fall in infant mortality over the past century to a reduction in overcrowding, cleaner water, and better sewage facilities. It then showed how, more recently, the advertising industry has pressurised mothers into believing that cleanliness is next to godliness and that their children need protection from the bugs lurking everywhere. The need “to kill all known germs dead” is screamed from billboards, radios, and televisions.
Just as there has been a trend towards an environment containing fewer microbes, an opposite trend has appeared in the number of people who have asthma and juvenile onset diabetes. This rise in the incidence of asthma cannot be explained by genetics alone, since it occurred too quickly—so it must reflect environmental changes.
For a while, many scientists thought that an increase in asthma must reflect increasing exposure to pollution. But the reunification of Germany, with the realisation that the polluted East had lower levels of atopic disease than the less polluted West, soon put paid to this idea.
A new theory emerged: the “hygiene hypothesis.” Eat Dirt charted, with amazing accuracy, the environmental studies that led to this elegant explanation. These were described with clarity by those who did the original research.
Viewers saw how living in close proximity to animals might protect humans from developing atopic diseases. Such protection, the programme suggested, might also arise from 20 people living to a house in West Africa. Antibiotic use, especially in infancy, might be associated with a higher prevalence of asthma later in life. Similar evidence showed that the hypothesis might apply to juvenile onset diabetes—the greater the number of infections, the greater the protection against developing the disease.
The European specialists were the stars of the programme. Perhaps this reflected their pre-eminence and intellect, and their role at the cutting edge of research into the role of infections in the causation of asthma and diabetes, and the use of vaccines in the treatment of multiple sclerosis and cancer.
They also had wonderful presentation skills. Either these coexist intrinsically with an interest in this particular subject, or Channel 4's researchers are particularly adept at discovering the best academics to interview. Thus a learned microbiologist, explaining how an immune system underchallenged by infection might attack pollen or house dust mites, talked of “the immune system going looking for a fight.” The same academic later explained how bacteria couldn't jump from a contaminated phone handset because “bacteria don't have wings.”
We were encouraged to accept that exposure to a little dirt might be good for us. Or, in the words of the microbiologist, “If we didn't see all the good E coli, we would get a lot sicker when we saw the bad ones.” When it comes to cleaning the house, perhaps less is more? The programme illustrated this beautifully by reconstructing a kitchen complete with filth—not a health hazard, but an opportunity to gain protection from atopy.
About halfway through, the programme began to meander, and I wondered how they would bring it to a close. We know that the optimal length of a lecture is about 20 minutes. Do programme producers know how long they can keep their viewers' attention on such difficult concepts? Stretching the data out over 60 minutes was probably a mistake.
When I have tried to explain the hygiene hypothesis to journalists, the reply has been, “So everyone should go back to having diarrhoea in infancy?” This programme did rather better in explaining the concepts to a non-medical audience. It also ended well, discussing some of the speculative work on the role of vaccinations, especially BCG and mycobacterium, in preventing asthma and other diseases. The brief asides, discussing terminal skin cancer and multiple sclerosis, were rather superficial and an unnecessary diversion.
Figure.
A filthy kitchen looks like a health hazard, but it may protect you from atopy