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Yupik in the Yukon Delta: Are they getting enough vitamin D?

Posted on: April 5, 2014   by  Brant Cebulla

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A series of questions people often ask is, “How do indigenous people living in the Arctic Circle (or close to) get their vitamin D? If vitamin D is so important, why have the Inuit been able to thrive without it?”

As most readers are well aware, we primarily get our vitamin D from sun exposure, in which our skin converts a cholesterol precursor called 7-dehydrocholesterol into (eventually) vitamin D3. Researchers estimate that in Africa, where the human genome evolved, humans relied on sun exposure to fulfill 90% of their vitamin D requirements (10% from food).

However, sun exposure is not nearly as prevalent in more northern regions like Europe, most parts of North America, and certainly the Arctic Circle. During the winter, the sun shifts its focus to the Southern Hemisphere. In consequence, the Northern Hemisphere receives little to no UVB, the wavelength responsible for inducing vitamin D production. So, during the winter, people in the Northern Hemisphere are getting little to no vitamin D from sun exposure.

The further north you live, the longer the period in which you can’t make any vitamin D from sun exposure. Each and every year, Arctic populations like the Inuit and Yupik have the least amount of time to make vitamin D compared to all other populations on the planet.

This raises many questions. Are Arctic populations deficient in vitamin D? If so, do they have high rates of vitamin D deficiency related diseases? Have Arctic populations quickly evolved to not need much vitamin D? Or, are they getting enough vitamin D from food sources to make up for the lack of sun exposure?

New research published in the International Journal of Circumpolar Health suggests that through a combination of summer sun exposure and food sources, Arctic populations may be getting enough vitamin D just fine.

Researchers from the University of Alaska Fairbanks looked at the diets and vitamin D levels of 497 Yupik people aged 14-92 living in the Yukon Kuskokwim River Delta between 2003 and 2005. The Yukon Kuskokwim River Delta is located in southwestern Alaska, and around 25,000 people live in the area, most of them Yupik.

The researchers wanted to know what the vitamin D levels were of this Yupik population, and they wanted to what their diet looked like, to see if their vitamin D levels might be explained in part by their diet.

For vitamin D levels, here’s what they found:

  • In general, vitamin D levels were sufficient and higher than expected. The mean level was 38.2 ng/ml.
  • The mean vitamin D level during times when you could synthesize vitamin D (i.e. summer) was 41.2 ng/ml.
  • The mean vitamin D level during times when you couldn’t synthesize vitamin D (i.e. winter) was 35.3 ng/ml.

Here’s what they found for diet:

  • The mean vitamin D intake from food was 604 IU/day, but there was great variability in the population; one standard deviation was 808 IU, meaning that 68% of the population received anywhere from 0 to 1,412 IU of vitamin D/day.
  • Locally harvested foods, like fish, fish roe, seal oil, game meat, game fowl, organ meats, shellfish and animal fat, accounted for 23% of the Yupik diet. The other 77% of their diet came from the marketplace.
  • That being said, locally harvested foods accounted for 90% of vitamin D intake, as opposed to marketplace foods only accounting for 10% of vitamin D intake.

The researchers concluded,

“Vitamin D status was predominantly sufficient throughout the year and across the participants. Endogenously produced 25(OH)D was apparent during the synthesizing months, but the expected drop in serum 25(OH)D during other months seemed mitigated by dietary sources, which we attributed to the use of local foods, consistent with a traditional lifestyle.”

One aspect not included in this study that would have given us additional insight is data on the Yupik’s sun exposure habits during vitamin D-synthesizing periods of the year. That would allow us to estimate how much vitamin D they might be getting from sun exposure.

It appears that the Yupik in this region are able to fulfill their vitamin D needs by getting sun exposure during the summer and mitigating the issue of lack of sunlight and UVB in the winter by eating lots of seafood with some vitamin D in it.

You can also infer from this data that the Yupik would get much more vitamin D if they only ate locally harvested foods. We’re left speculating that traditionally, they may have gotten even more vitamin D from food, before they become more reliant on the marketplace for food.

Arctic populations and their vitamin D requirements and intakes are fascinating subjects. We need further research in the area to understand if they’re meeting their requirements or if their requirements somehow differ from the rest of the world.

In this population, the Yupik in the Yukon delta, they appear to be getting just enough vitamin D. They could, and maybe should, be getting even a little bit more vitamin D, if they returned to becoming solely reliant on locally harvested foods.

Source

Luick B et al. Locally harvested foods support serum 25-hydroxyvitamin D sufficiency in an indigenous population of Western Alaska. Int J Circumpolar Health, 2014.

Notes

This study might make you ask, then can I rely on food rather than supplements for vitamin D during the wintertime? The answer is probably no.

Fish and wild game made up about 25% of the Yupik’s diet in this study, a percentage that far exceeds the makeup of seafood in the average Western diet. Even if you aimed to change your diet so that 25% of your energy intake came from seafood, it is unlikely you’d be able to maintain this intake on a daily basis.

Furthermore, their seafood came from a very specific and “wild” region. The amounts of vitamin D in seafood from grocery stores and marketplaces are much more ambiguous and unreliable. Different harvesting practices (farm vs. wild) and ecosystems around the world influence the amounts of vitamin D in seafood, to the extent that it would be difficult to expect consistent amounts of vitamin D to be in particular types of seafood.

1 Response to Yupik in the Yukon Delta: Are they getting enough vitamin D?

  1. Ron Carmichael

    I’m left with the curiosity regarding whether these peoples handle vitamin D in a more efficient metabolic way as well. Studying those that have left the lifestyle of their forebears for the “marketplace” in a major way, and seeing what their levels are, and how they respond to moderate doses of D3 would be fascinating. Also what their endogenous mercury levels are…

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