We are constantly being warned about sun exposure and skin cancer. Still, it is important that we get plenty of vitamin D from sunshine - as long as we avoid getting burned. Vitamin D prevents and cures many diseases, and it may not only be the Mediterranean diet alone but the increased sun exposure and higher vitamin D levels that help people in Southern Europe avoid cardiovascular disease and other ailments.
It is a good idea to get used to the spring sun and gradually build a tan without getting burned. It is only during the summer where the sun is adequately high in the sky that we humans are able to synthesize vitamin D from cholesterol in our skin. In spite of this, many people spend the major part of their day indoors or lather themselves in sun factor cream, which can block the vitamin D synthesis. Many kindergartens even have a policy of applying sun cream to the children's skin from the early morning. As a result of the widespread use of sun factor cream, large parts of the population remain pale all summer, and this is visible proof that they are not producing vitamin D. The lack of this nutrient may have both short- and long-term consequences.
Vitamin D and its many functions
Vitamin D is a hormone-like substance that is very important for bones, teeth, immune defense, cardiovascular system, blood pressure, energy levels, mood, anti-inflammatory response, anti-ageing, and prevention of diabetes, cancer, and cardiovascular diseases. As all cells in the human body are equipped with vitamin D receptors, a vitamin D shortages may affect us in many different ways.
Vitamin D synthesis is determined by evolution, culture, and latitude
It is assumed that our African ancestors became evolutionarily adapted to synthesize around 500 micrograms of vitamin D daily from exposure to sunlight. This amount is around a hundred times greater than our current reference intake (previously known as RDA) of 5 micrograms for adults. Just for the sake of comparison, half an hour of sun exposure to the entire (naked) body produces around 250-625 micrograms of vitamin D. A person wearing light summer clothing produces around 30 micrograms of vitamin D with about 10-15 minutes of sun exposure.
In order for our skin to synthesize vitamin D, the sun must be sufficiently high in the sky. Therefore, it is controversial when health authorities encourage us to stay out of the sun or recommend that we cover up in the middle of the day. We can get too much sun, but we cannot produce too much vitamin D, as the synthesis of the vitamin regulates itself. If a person burns easily he or she should limit their sun exposure to 20-30 minutes and then apply (eco-friendly) sun factor cream.
Vitamin D synthesis on a sunny summer day
|Indoor work and activity:||0 micrograms|
|Woman (veiled but with bare hands):||2 micrograms|
|Lunch break (outdoors):||45 micrograms|
|Being outdoors for 2 hours:||250 microgram|
|Being outdoors (in swimsuit) for 2 hours:||500 micrograms|
The listed figures are merely indicative and may vary depending on factors such as age, skin type, time of day etc.
How much vitamin D do we actually need?
A normal diet provides less than 5 micrograms of vitamin D. This dosage is far less than we can synthesize on a warm summer day. Leading experts criticize the low reference intake and recommend as much as 100 micrograms daily (including the body's own vitamin D synthesis) for optimal health. Actually, the need for vitamin D most likely varies from person to person, as some have an easier time producing the vitamin and storing it in the liver for later use than others. A lot depends on skin type, age, body enzymes, plus liver and kidney function. In addition, overweight people and diabetics are more likely to have too little vitamin D and therefore have a greater need for the vitamin than others.
Misleading research with too little vitamin D
Because the official recommendations for vitamin D levels are that low, nearly all studies designed to investigate how vitamin D affects various diseases are misleading and worthless, simply because the dosages used in this research are far too low. What is more, these studies fail to take other factors into account such as the time of year (summer or winter?), vacations in sunny places, use of sunbeds, and other lifestyle factors that have a much greater impact on vitamin D levels than the negligible amount of vitamin D given to the study participants in supplemental form. In order to study the optimal effect of vitamin D, one would have to use optimal dosages obtained by means of sun exposure or supplementation.
It is also a fact that vitamin D is ignored in scientific studies of all kinds where it is not consumed or injected. Here, it would be most relevant to observe sun exposure or lack of the same and make a note of it.
The Mediterranean diet, sunshine and outdoor living
It is well-known that people in the Mediterranean area have a lower rate of cardiovascular disease, they have fewer cancers, and they generally live longer. This, experts say, is largely due to their diet. However, it may be the sun that plays the most significant role. It is much higher in the sky in those countries, and people - especially in the rural parts - have a different outdoor culture that exposes them to much more sunshine and, consequently, an increased synthesis of vitamin D.
Just like the Mediterranean diet normally gets all the attention when it comes to explaining why people in southern Europe have better health, the low rate of cardiovascular disease and European cancer types among Greenlandic hunters is ascribed to their higher intake of omega-3 fatty acids from oily fish, seal, and other types of seafood. One may rightfully ask if it could be the relatively large amounts of vitamin D they get from consuming seal liver, and perhaps also the selenium that they consume in large quantities from their fish diet.
Iowa State University: New promise for diabetics with vitamin D-deficiency. ScienceDaily. 2016
Steen Ahrenkiel. D-vitamin behov og mangel i Danmark. Biokemisk forskning 2009
Clark LC et al: Effects of Selenium Supplementation for Cancer Prevention in Patients with Carcinoma of the Skin. Journal of the American Medical Association: 1996
Klein EA et al. Vitamin E and the risk of prostate cancer: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). Jama 2011.
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