health

Ed Yong has a great account today of some research from Alan Cooper's lab on the oral microbiome in pre-agricultural and post-agricultural Europeans: "Prehistoric Plaque and the Gentrification of Europe’s Mouth".

The hunter-gatherers had a diverse array of bacteria including several groups that are associated with good health. That fits with the relative absence of tooth decay or gum disease among modern or prehistoric hunter-gatherers. “They were at the end of a long period of happy co-evolution between us and oral bacteria,” says Cooper.

The advent of farming disrupted that tango. After the Agricultural Revolution, as humans began to chow down upon barley, wheat and other domesticated crops, the diversity of the mouth microbes fell, and species associated with oral diseases became more common. “Eating all this soft squishy carbohydrate and leaving it lying around the base of your teeth is effectively inviting in a whole new range of bugs to take up permanent residence in your mouth,” says Cooper.

I'll have some more comments on this new research when I can sit down to write them up. I've been waiting for this to come out for quite a long time -- I first heard about the research almost three years ago. The potential to characterize oral ecology across time is immense, and we have some excellent data on dental pathologies across the entire timespan. Caries and other dental pathologies are very new in human populations, and although starchy diets have been blamed, very little has been known about how oral bacteria themselves may have become more pathogenic over time. This study is really great because it opens a new door to looking at this evolution across time. We will need to compare this record with the evidence for morphological change in teeth across the same time span. Smaller teeth may have been a consequence of selection associated with dental pathology in agricultural peoples.

Next we will need to compare across space -- including greater sampling of oral microbiome variation among living humans. This is another new area in which we know more about prehistoric people than we do about living human variation!

Maggie Koerth-Baker, on "How space radiation hurts astronauts". I did not know about this part:

Cucinotta calls this pre-flight calibration. Scientists take a blood sample from an astronaut before the launch. While the astronaut is in space, the scientists divide that blood sample up and expose it to various levels of gamma rays — the kind of damaging radiation we're used to dealing with on Earth. Then, when the astronaut comes back, they compare those gamma ray-affected samples to what has actually happened to the astronaut while in space. "You see about a two-to-three fold difference across the population of astronauts," Cucinotta told me.

The sample size of astronauts is small enough that I was surprised to see significant effects for one condition: cataracts. The article notes that the Mercury and Gemini astronauts had less spaceflight time than Mir and Skylab cosmonauts and astronauts, which is obvious, but I wonder how they control for the extensive flight time of astronauts who were former test pilots and the consequent history of radiation exposure before going to space.

I lectured on pigmentation in my introductory class this week, and this recent news story is relevant: "Redheads may be at higher risk of melanoma even without sun". The article describes experiments in which mice were kept out of UV radiation entirely for the control portion of another experiment, when the researchers noticed a clear difference:

When researchers compared skin samples of the different mice, the redheaded mice showed almost three times as much damage due to oxidative stress, leading authors to conclude that pheomelanin was the culprit.

Conversely, the brown-black pigment, eumelanin, possibly acted as an antioxidant in the black-haired mice and counteracted the red pigment's damaging behavior. The albino mice lacked either type of functioning pigment.

The genetic pathway underlying pigmentation is fairly well understood, but there are still unknown biochemical aspects of these molecules, which are locally quite concentrated in some tissues. The research described here was in Nature recently, by Devarati Mitra and colleagues [1]. The conclusion of that paper reflects on the implications for understanding human pigmentation variation:

Further evidence suggesting an ultraviolet-radiation-independent red hair/fair skin melanoma risk is the observation that although darker-skinned individuals have a significantly lower risk of melanoma than lighter-skinned individuals, the sun protective factor (SPF, a measurement of sunburn protection) of darker skin has been estimated at only in the range of SPF 2.0–4.0 (ref. 28). In addition, sunscreen (typically SPF 20–40) has shown weak efficacy in protecting against melanoma, unlike its protection against cutaneous squamous cell carcinoma. There are numerous potential explanations for the sunscreen-melanoma data including the possibility that ultraviolet radiation shielding may protect against only one of several carcinogenic mechanisms—with the intrinsic pheomelanin pathway representing an additional contributor to melanomagenesis via ultraviolet-radiation-independent means. These data are not evidence against a role for ultraviolet radiation in melanomagenesis. Indeed, the effect of ultraviolet radiation is likely to exacerbate this mechanism, such that ultraviolet radiation shielding and sunscreen remain extremely important for skin cancer prevention. However, further preventative strategies may be essential to optimally diminish melanoma risk in the most susceptible individuals.

Most teachers who present human pigmentation as a defense against UV radiation gloss over the relatively low SPF of darker skin. That's not to say it isn't helpful in reducing UV-induced damage, but it's not a perfect defense. In case you wonder why most juvenile humans retain hair covering for their heads, that low SPF protection from melanin is part of the explanation.

References

Gina Kolata reports on a surprising result for a long-term study of diet and exercise in the treatment of type 2 diabetes: "Diabetes Study Ends Early With a Surprising Result".

The study randomly assigned 5,145 overweight or obese people with Type 2 diabetes to either a rigorous diet and exercise regimen or to sessions in which they got general health information. The diet involved 1,200 to 1,500 calories a day for those weighing less than 250 pounds and 1,500 to 1,800 calories a day for those weighing more. The exercise program was at least 175 minutes a week of moderate exercise.

But 11 years after the study began, researchers concluded it was futile to continue — the two groups had nearly identical rates of heart attacks, strokes and cardiovascular deaths.

One expert quoted in the article thinks that the large effects of smoking cessation, statin drugs and blood pressure medications may swamp the small effect of diet and exercise. Swamp the small effect of diet and exercise on type 2 diabetes in obese patients? Wow.