It’s too late for your teeth
Angela (3 PM Micro) told me she would be late for class on Wednesday, due to a dental appointment, and I told her about this news alert from io9.com describing research from Nature Genetics. (Sorry, paywall!) Scientists at Australia’s University of Adelaide isolated preserved dental plaque from excavated human remains covering a range of 7500 years, buried in Northern Europe. DNA was isolated from the preserved remains that gave a snapshot of the microorganisms living in the human oral cavity during different historical eras, and that DNA was analyzed to determine the diversity of those organisms.
The interactions of organisms in the mouth, and their relative ability to cause disease is nothing new. Longtime BIO230 fans may recall this posting from March 2011, which proposed a novel way to inhibit tooth decay by introducing a new bacterium into the mouth. This current report indicates that dental caries may be a very new problem in human health, and that it may coincide with the development of agriculture and the concurrent shift in human diet to one richer in carbohydrates. The researchers found that the diversity of microorganisms associated with the mouth have significantly decreased in phylogenetic diversity over the past 7500 years, and today’s mouths are much more heavily colonized by Streptococcus mutans, a species that is the primary agent in dental caries.
The researchers characterized two shifts in microbial diversity in the oral cavity, the first several thousand years ago coinciding with the introduction of agriculture and the shift in human diet, and another one 150 years ago during the Industrial Revolution. It was at this time that processed sugars and flour became widely available throughout society. The most significant decrease in microbial diversity occurred at this time, as the figure shows. The authors of the study argue that the human mouth exists in a constant diseased state in modern times, in large part attributable to the loss of bacterial diversity and the dominance by caries causing strains.
The comment thread on i09 then degenerated into an argument detailing the virtues and drawbacks of the paleo diet, as a possible way to “regress” the oral microbiome to a state resembling those that ancestral humans might have had. There are very few peer-reviewed articles looking at the positive and negative effects of altering the diet to make one rich in protein/lacking processed grains. One review article from 2009 summarized controlled human studies, and found that there were “promising” results, but no clear cut benefits from such a diet, and furthermore that the limited diet could actually be detrimental due to lack of vitamins and calcium. Additionally, a broad metagenomic analysis of the human gut microbiome indicated that there is actually not a large diversity of organisms between distant geographical locations. Humans show shifts in the microbial flora during different times in our lives (or perhaps age-related changes are due to the organisms influencing us), however there was no real correlation with different groups of microorganisms with any particular cultural group. That latter study strongly argues that there is very little we can do to broadly influence our microbial flora with any degree of success.