Sun Exposure North of the Arctic Circle
The August Nutrition Society Paper of the month is from British Journal of Nutrition and is entitled ‘Vitamin D in serum is influenced by diet and season in North Greenland: indicators of dermal 25OHD production north of the Arctic Circle’
No need to worry about vitamin D deficiency if you live in North Greenland. This is the conclusion in a study done 500 kilometres north of the Arctic Circle. The study was conducted by Arctic Health Research Centre in Denmark and published in British Journal of Nutrition.
The weather in North Greenland often calls for a jumper and jeans rather than T-shirt and shorts as temperatures in midsummer peak around 70 °C. Still, Inuit (Eskimos) and Caucasians in North Greenland do get sufficient levels of vitamin D from the sun. This unexpected finding is contrary to previous beliefs.
We depend on the sun for dermal vitamin D production. When the sun’s beams reach the Earth at the Equator the passage through the atmosphere is short and people produce ample vitamin D in the skin. However, the oblique passage through the atmosphere at the North Pole reduces the intensity of the radiation from the Sun and this was expected to restrict vitamin D production in circumpolar populations. ‘Contrary to this we found indicators of a marked vitamin D production in people living 500 kilometres north of the Arctic Circle’, states Stig Andersen, head of Arctic Health Research Centre at Aalborg University Hospital in Denmark, who conducted the survey.
The researchers measured vitamin D levels, over a full year, in 97 Caucasian Danes and Inuit in the Disco Bay area in North Greenland. They found a marked increase in vitamin D during spring and summer, after adjusting for age, gender, use of vitamin D containing supplements and the intake of vitamin D rich seal, whale and fish from the local hunt.
Sunny Greenland or Greece
The sun makes all the difference. The polar night starts in early December and the sun doesn’t rise until mid-January. This is as much of a guarantee as you can get for absolutely no dermal vitamin D production. Thus, people depend on building up vitamin D depots during spring and summer. According to Stig Andersen it seems that they are able to do this. Still, if you plan on moving to North Greenland he still recommends vitamin D supplements during winter, just as if you were living in Manchester or Aalborg.
Dermal Vitamin D production in Greenland is linked to the climate. Spring in the Disco Bay area is characterised by a series of sunny days, as this is a high pressure area. And as we move into July the nights become just as sunny. Also, the intensity of the light is amplified by the reflections from ice, snow and water as there are no trees or bushes to absorb the light.
Vitamin D protects from osteoporosis and muscle weakness and it has been associated with cancer and heart disease. All participants had vitamin D at levels where the risk of disease is low.
Inuit hunters spend up to 16 hours outdoors daily in February with temperatures of -20°C. The temperature rises during spring and hunters develop a sun tan similar to a ‘farmer-tan’. Previous research has shown that the Inuit develop cataracts due to the UVB-radiation that also gives rise to dermal vitamin D production, says Stig Andersen.
Finally, our results suggest a genetic difference in vitamin D metabolism between Inuit and Caucasians. This is the target for new research on vitamin D in Greenland, states Stig Andersen.
Authors: Stig Andersen, Anna Jakobsen, Peter Laurberg
Arctic Health Research Centre
Aalborg University Hospital
Nutrition Society Paper of the Month
Each month a paper is selected by one of the Editors of the five Nutrition Society Publications (British Journal of Nutrition, Public Health Nutrition, Nutrition Research Reviews, Proceedings of the Nutrition Society and Journal of Nutritional Science). This paper is freely available for one month.