The most recent paper by Dr. Martine Luxwolda and colleagues of the University Medical Center Groningen in Holland is so remarkable that this is the final part to the three blog series covering the paper. The same group previously discovered that free-living hunter-gatherers around the equator have vitamin D blood levels of about twice the modern American, about 45 ng/ml.
Now, they studied how vitamin D levels change with age, how levels change before, during, and after pregnancy and how warm water surface lake fish consumption affects vitamin D, including 25(OH)D₂ and 25(OH)D₃ levels. Today we discuss their fish consumption, and the surprising appearance of ergocalciferol or D₂ in the blood of some of these native populations.
We will concentrate on a Bantus tribe, the Sengerema. They live on the shores of Lake Victoria, eat a lot of fish, and wear clothing that covers the entire body except for the lower arms and faces, substantially lowering their non-pregnant vitamin D levels. For example, the Sengerema women had 25(OH)D levels of 30 ng/ml when not pregnant but jumped to 55 ng/ml when pregnant for reasons discussed yesterday. Some non-pregnant women were as low as 12 ng/ml and some as high as 57 ng/ml, indicating the Sengerema women varied widely in sun exposure or their vitamin D genetics. Males were not tested.
The surprising thing is that 17% of the vitamin D in the blood of Sengerema women consisted of 25(OH)D₂. Furthermore, their blood DHA (a component of fish) correlated rather strongly with 25(OH)D₂ levels. Fish are thought to contain D₃, not D₂, and the authors regretted not having any Lake Victoria fish to sample for D₂ levels. Blood DHA also weakly correlated with 25(OH)D₃, so the fish might contain both D₂ and D₃. To my knowledge, mushrooms and sun dried alfalfa are the only foods containing significant amounts of naturally occurring D₂.
Still, the majority of their vitamin D status depended on sunlight, despite their penchant for wearing clothes that cover up most skin. In order to get all their vitamin D from fish, the authors estimate each woman would have to consume about 5 pounds of fish per day.
However, the Same people (not same, but the Same), another Bantus tribe not living on Lake Victoria, eat an intermediate amount of fish. The Same tribe had the lowest 25(OH)D₂ levels (most were normal, that is undetectable). The authors conjecture another D₂ source may exist in Lake Victoria fish, or a source of D₂, such as a fungi, yeast or algae, enters the food chain around Lake Victoria. It is not mushroom or alfalfa country.
A few things to pull from this:
- D2 is in the humans who live around Lake Victoria, but we have no idea where it came from.
- Even equatorial tribes that wear a lot of clothing (Bantus) can be vitamin D deficient, but the incidence is nowhere close to the United States.
- Vitamin D status in indigenous populations: Part 1
- Vitamin D levels throughout pregnancy: Part 2
- Fish consumption and vitamin D status in native populations: Part 3