How much time did our ancestors spend in the sun? And does it matter for your health today?
A new study provides an interesting clue.
From sunny Africa to the dark north
Our human ancestors emigrated from eastern Africa and spread across the entire planet. That often meant that the sun became much weaker. Since vitamin D is produced by our skin when in strong sunlight their levels of vitamin D dropped rapidly when moving north, which may have led to severe health problems.
In an extremely short time, evolutionary speaking, the ancestors of northern people developed lighter skin. They rapidly shed their built-in sun protection, likely to catch all the sun and vitamin D that they could.
In not-so-sunny Sweden, where I live, a lot of people have severe shortage of vitamin D during the winter, despite having light skin. Statistically such deficiency is correlated with just about every disease there is. Such correlations doesn’t prove that the deficiency leads to all these diseases, but it’s possible that it contributes.
What is normal?
How much vitamin D is “normal” to have in your blood? That’s a common question. According to my lab between 75-250 nmol/L is normal, and below 75 is considered a deficiency.
- (Divide by 2.5 for values in ng/ml, i.e. 30-100 ng/ml would be considered normal)
This means that all the patients I’ve tested during the winter in Sweden are deficient, if they haven’t travelled south or taken a vitamin D supplement. Extreme deficiencies of 20 or less isn’t uncommon. The lowest I’ve seen is 14 nmol/L.
These extreme deficiencies have often been tired patients, sometimes with a history of winter depressions. Taking supplemental vitamin D has several times led to remarkable recoveries within a few weeks. Well done trials have also shown significant such effects.
A study of traditionally living people in sunny East Africa gives us a clue to what’s normal. These people all have dark skin, built in sun protection. They spend most of the day outdoors but avoid strong sun when they can. Perhaps their skin and sun habits are similiar to our ancestors (who lived in the same environment).
The average vitamin D level was 115 nmol/L (46 ng/ml). The lowest level found was 58 and the highest 171. Here is the study:
- Luxwolda MF, et al. Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. Br J Nutr. 2012 Jan 23:1-5. [Epub ahead of print]
How do we get vitamin D during the winter?
For those who don’t spend their days outdoors in a sunny climate there are three good options to get vitamin D:
- Strong sun (travelling south or using a tanning bed with the right wave lengths)
- Eating fatty fish (350 grams daily may give you 2 000 units)
- Supplements (the cheapest, easiest way)
Personally I’ve been taking 4 000 units daily (recently increased to 5 000). I skip it during sunny summer times. This fall my vitamin D level was 95 nmol/L.
Less than an average Maasai but not too bad.