The advent of the paleolithic diet makes one realize that there are many other ways that modern lifestyle differs from that of our long-ago ancestors besides food. They had no bright lights interfering with sleep, they probably ate at irregular times and fasting was likely a regular occurrence, they were more often exposed to cold, heat, and sun, they had primitive or no footwear, and so on. One other thing they didn’t have was a high standard of cleanliness. They had no soap, no antibiotics, and no concept of the germ theory of disease.
In our day, it’s been suspected that living in an ultra-clean environment with little exposure to bacteria and parasites may be the cause of some illnesses, especially allergic and autoimmune illnesses. The idea is that exposure of the immune system to microbial agents is necessary for the proper regulation of immunity. This is known as the hygiene hypothesis.
It seems that the hygiene hypothesis may be able to explain some other diseases of civilization, such as Alzheimer’s. Immune function is known to be involved in the pathogenesis of this disease, so it stands to reason that hygiene could be involved also. A recent epidemiological study, Hygiene and the world distribution of Alzheimer’s disease, found a strong positive correlation between level of hygiene in a country and its rate of Alzheimer’s. The researchers used a number of variables as proxies for level of hygiene, such as parasite prevalence, historical disease prevalence, and level of urbanization. Here’s one striking graph of parasite prevalence vs Alzheimer’s rates.
This is an association of course, cause and effect have not been proven.
This is but one example of how our modern way of life could be contributing to poor health. A recent paper by Gordon Gallup and co-authors, Evolutionary Medicine: The Impact of Evolutionary
Theory on Research, Prevention, and Practice (PDF), discussed a number of ways that modern lifestyle could result in poorer health:
We review recent evidence for a growing number of discrepancies between our
contemporary existence and evolutionary history which have the potential to impair
and undermine features of human mental and physical health. Included in this
review are health issues related to bottle feeding, caesarian section, infection,
cleanliness, fever, exercise, diet, mate choice, contraception, semen sampling, and
body odor suppression.
Note that infection and cleanliness are two of these “discrepancies between our contemporary existence and evolutionary history”. Regarding infection, they write:
The skin is an important line of defense against infection. The easiest entry
sites for infection are at the superficial level; cuts, scrapes, and scratches, typical
innocuous injuries which create a pathway for microbes to enter the body. It is not
surprising therefore that one of the most vital components of the human immune
system is embedded immediately beneath the skin….
In the ancestral environment, humans were subjected to a wide variety of
circumstances in which cuts and scrapes were common. It can be argued that
exposure to viruses and various other microbes through these entry points tended to
promote immune system function. Many of us are now removed from conditions
where cuts and abrasions are a part of the norm, thus making ourselves more
vulnerable to infections that may otherwise be tolerated. Furthermore, it is common
practice to apply an antibiotic ointment immediately after such an injury, thus limiting
exposure and perhaps doing ourselves a disservice, particularly during
So, we don’t cut or scrape ourselves much these days, and that could – and probably does – result in worse immune function.
What can we do about all this? I’m not sure – unless you want to deliberately inflict cuts and scrapes on yourself – not a recommended practice – or expose yourself deliberately to sick people. It would seem to follow that outdoor activities involving exposure to dirty conditions, as well as the occasional cut or scrape, may be healthy for reasons not involving exercise.
Just FYI, there’s a probiotic called Prescript-Assist that contains 29 different strains of bacteria, most of which come from dirt. (I have no association with the product.)