How much sun do we need? A heated argument has broken out among scientists about this question. On the one hand, dermatologists have been warning against too much UV radiation for years because it can cause skin cancer. However, recent studies show that excessive abstinence from the sun also brings problems: a poor supply of vitamin D and thus not only an increased risk of osteoporosis, but also of common diseases such as cancer, cardiovascular problems, diabetes, Infections or Alzheimer’s.
At the same time, a high vitamin D level can apparently extend life. This is the result of researchers from the universities of Ludwigsburg and Graz. Over eight years they examined 3200 people who were on average 62 years old. Those subjects whose vitamin D levels were lower than recommended had a twice as high risk of death, so the result. In addition, too little vitamin D in the blood apparently increased the likelihood of heart failure, a stroke or cancer. Other international studies provided similar data.
The flood of new studies on this topic can be explained by an important discovery: “The breakthrough came when science recognized a few years ago that there are specific vitamin D receptors in almost all tissues and organs. “They are not there by chance,” says Nicolai Worm. The Munich-based nutritionist has been dealing with the topic for ten years and has summarized the state of research in his book “Heilkraft D” .
No vitamin D without UVB rays
According to this, vitamin D experts are convinced that this nutrient is involved in a large number of body processes and is therefore of much greater importance than previously assumed. But: in order for the organism to get enough of it, it needs sun, which covers around 90 percent of its needs. More precisely, it is the UV-B rays that set a chemical process in motion in the skin, whereby vitamin D is formed. Strictly speaking, this means that the substance is not a vitamin because, by definition, the body cannot and does not have to supply it itself. Vitamin D is a hormone, say nutritionists.
But as soon as someone asks for more sun, skin specialists are alarmed. “We must not try to compensate for a possibly bad vitamin D level with an excess of UV radiation,” says Rüdiger Greinert, biophysicist at the Dermatological Center Buxtehude and warns against jumping to conclusions – much is still unclear. His concern is that people will become careless again and remain unprotected in the sun for hours.
A quarter of an hour in the sun is enough
Even the vitamin D experts have no license for excessive sunbathing. Because a lot doesn’t help much: Depending on the skin type, about 15 minutes are enough on average for an adequate vitamin D supply, but daily or as often as the sun shines. Preferably between 10 a.m. and 2 p.m., when the UVB radiation is at its highest, and without sun protection because it inhibits production, says Worm. After about 20 to 30 minutes, the so-called vitamin D synthesis is over anyway – a natural protection of the body against overdosing. Anything beyond that is of no use, so the following applies again: get out of the sun or apply lotion and protect. Sunburn, even redness, is a risk and should be avoided at all costs.
The Robert Koch Institute (RKI) has determined that vitamin D supply is actually problematic in Germany. About 63 percent of children and about 58 percent of adults have too little vitamin D in their blood. Around 10,000 children and adolescents and around 4,000 adults were examined.
A frightening result, especially since it is disputed among experts whether the value of 20 micrograms per liter taken as a basis by the RKI is even sufficient for optimal supply. “Various limit values are being discussed,” says ecotrophologist Birte Hintzpeter from the RKI, who evaluated this study. “We have applied a limit value that is based on scientific knowledge.” However, it is still based on the importance for the bones, because we know that a severe deficiency leads to the softening of the bones.
A slight undersupply can damage in the long term
However, it is not just the obvious deficiency that is problematic. “We are getting more and more data that even a slight undersupply is unhealthy in the long term,” says Hans Konrad Biesalski, Professor of Nutritional Medicine at the University of Hohenheim. He compares this to a car that always runs on a minimum of oil. “You can drive it for a long time. But at some point the car is broken because the small amount leads to signs of wear and tear that would not have occurred with good care.”
There are two main reasons for the poor supply of vitamin D. On the one hand, there is the lifestyle: working people often sit in closed rooms all day, and many children spend too little time outdoors. On the other hand, it is the geographical location. In Germany, the sun doesn’t shine often or intensely enough. Especially in winter we are undersupplied for months because the body cannot create an endless supply.
Diet can also hardly make up for a deficit. The German Nutrition Society recommends a daily dose of five micrograms for adults and ten for infants and people over 65 years of age – but these are also rarely achieved. Few foods contain any significant amounts of vitamin D: oily fish such as herring or salmon and mushrooms, and very little is found in dairy products. But eating fatty fish every day or drinking gallons of milk is not a solution either. And even if this were enough for the recommended intake, this alone would not achieve a sufficiently high vitamin D level.
Children and the elderly are particularly at risk
As a result, almost everyone is affected by an undersupply, but there are special risk groups. These are children and adolescents, because if the bone structure is not optimal in early years, osteoporosis threatens in old age, says Biesalski. In addition, the elderly, especially women, and people with darker skin are often dramatically undersupplied. In seniors it is because the skin loses the ability to generate vitamin D through the sun with increasing age – in over 65-year-olds it is still 20 percent. They are particularly dependent on foods with vitamin D, says Biesalski. Dark-skinned people would have to sunbathe longer because of the pigmentation. In southern regions this is not a problem, in northern regions it is.
Nevertheless, experts advise against buying vitamin D supplements on your own. There is still a lack of meaningful studies that clarify, for example, whether and in what dose supplements should be used, says RKI employee Hintzpeter.
So what remains for now is a conscious but moderate use of the sun. The tanning bed is not an alternative, warns skin expert Greinert: “Only recently the International Agency for Cancer Research announced that the radiation from solariums is highly carcinogenic.”