In a counterintuitive finding, scientists have discovered that levels of vitamin D deficiency in prehistoric Middle Eastern farming communities were four times as severe as those found in modern-day Greeks.
The discovery was made possible because the production of dentine – the main component of teeth – is strongly dependent on vitamin D.
When a person is deficient in the vitamin, dentine production is interrupted. The result, over a lifetime, is that each tooth, in cross-section, presents a permanent record of vitamin D levels, with its presence or absence deducible by layers of mineralisation.
Teeth are in general very strong structures, resistant to biodegradation, and thus often remain in burial sites long after other body parts have rotted away. They are also chemically stable, meaning that each tooth’s “dentine diary” remains readable, sometimes for millennia.
Utilising this handy marker, first discovered in 2016, a team led by Megan Brickley of McMaster University in Canada combined their own work with four previous studies of dentine concentration in human teeth, covering periods from the late Pleistocene – around 20,000 years ago – up to the present day.
The earliest of the studies was done in 1956, and involved tissue sampling of 233 teeth from archeological sites and modern sources. All four earlier studies were re-examined to correlate dentine mineralisation layers with age.
The raw data was also corrected for a range of other factors, including changes in atmospheric ozone concentration and the distance between the Earth and the Sun, both of which affect the intensity of ultraviolet light – and hence vitamin D production.
Corrections were also made on the basis of known clothing styles and fabric choices, both of which can affect that amount of UV light actually reaching the skin to trigger vitamin D production.
The team found that the earliest evidence of vitamin D deficiency came from the late Pleistocene era, in four out of five teeth recovered from a site at Mount Carmel in Israel.
Two of the affected teeth might be of Neanderthal origin, although current methods aren’t powerful enough to be definitive, and that, write Brickley and her colleagues, could be significant.
A previous analysis claimed the two teeth, likely from two individuals, to be evidence that Neanderthals suffered from vitamin deficiency. Brickley’s team concludes the evidence isn’t strong enough to make the call.
In broader terms, though, the team’s paper – published in the journal Current Anthropology – shows that vitamin D deficiency, far from being a modern condition, has been around at least since farming began.
However, some evidence suggests that it has become more severe in the wake of the transition from small-scale agriculture and pastoralism to large-scale complex urban societies.
Teeth from Greece in 1948, the scientists found, had four times the levels of deficiency – enough in several cases to have caused rickets – than those from farmers in the Middle East 5000 years earlier.
The exact role of vitamin D in a number of areas to which it is linked – including health and skin pigmentation – remains unknown. Brickley and her colleagues hope their data will inform further investigations into how it has shaped, and continues to shape, civilisation.