The Leiden biophysicist Frank de Gruijl was always very skeptical when someone brought up the positive effects of UV radiation. For years, he was an expert in the field of UV radiation and skin cancer at the LUMC, on various committees at home and abroad. He advised, among others, the Health Council and the Dutch Cancer Society. “I was always on the side where they said avoid UV radiation as much as possible, because it causes skin cancer. But on the other side there was always someone who said that we also need it to stay healthy. And over time there were more and more. ” About ten years ago his curiosity won over his skepticism, and De Gruijl started researching beneficial health effects. “I thought those guys were just frustrating the discussions. But I have to say that they did have a point. ”
We humans love the sun. But we have to be careful with it. UV radiation from the sun causes skin aging and damage in the DNA of skin cells that can later lead to unbridled growth: cancer.
Skin cancer is the most common cancer. More than 900 people die of it every year, and around 70,000 Dutch people are told they have it – at least four times as many as 25 years ago. That number is rising much faster than can be explained by population growth and aging, and RIVM expects this to continue. The most important cause is probably the sun-loving behavior of people: in recent decades we have been in the sun for longer and more often, in countries with a stronger sun power than at our latitude.
Sensible tanning is therefore the motto. But what does that mean? The opinions of dermatologists on this differ. Most insist on never going out without a good layer of sunscreen, wearing covering clothes, and avoiding the sun between 11am and 3pm. “A little UV light is also not good,” says Tamar Nijsten, head of the dermatology department at Erasmus MC in Rotterdam, “just as smoking a little is not good either”. Yet a small group is against such an absolute ban, because of the positive effects that UV radiation also has. That group argues for a more nuanced message.
“Dermatologists in Australia and the United States are especially zealous,” says De Gruijl. “And skin cancer is also a huge problem there. That’s because Australians are the descendants of English and Irish, just like in the US. From an evolutionary point of view, that light Northern European skin does not belong there, the sun power is higher there. ”
The sun power, expressed in the UV index issued daily by the KNMI, weighs the combustion strength of the UV rays that reach the earth. UV light can be distinguished in three colors: UV-A, UV-B and UV-C. The most harmful, UV-C, is blocked by the ozone layer. UV-B, with a wavelength of 280 to 315 nanometers, does pass partly through the atmosphere. It induces the tanning of the skin and is the main cause of skin burns. Less than 5 percent of the UV light on Earth is UV-B, but this determines 80 percent of the combustion strength. The vast majority is UVA. This is possible thanks to longer wavelengths through clothing and glass, and it determines 20 percent of the sun’s combustion strength. It penetrates deeper into the skin, where it attacks collagen and elastin, resulting in wrinkles and skin aging.
In the Netherlands there is far too much emphasis on lubrication
Frank de Gruijl biofysicus
In the Netherlands, we have to deal with the sun in a different way, De Gruijl thinks. “There is far too much emphasis on lubrication here. It is much more important for people to moderate exposure. A disadvantage of sunscreen creams is that people feel they are protected, so they stay in the sun longer than their skin can handle. ”
This is confirmed by Vigfús Sigurdsson, head of the dermatology department at UMC Utrecht. He is more flexible with the ‘smear message’. “Most importantly, don’t get burned,” he says. “Burning, with pain and blisters, especially at a young age, increases the risk of melanoma and basal cell carcinoma later in life.” In addition, long-term exposure to UV radiation should be avoided, he says. “People who spend a lot of time outside, or who regularly use the tanning bed, have a higher risk of squamous cell carcinoma, as well as basal cell carcinoma.”
The three forms of skin cancer that Sigurdsson mentions, basal cell carcinoma, squamous cell carcinoma and melanoma, are the best known. The former is the most common and the least malignant; the latter is the least common but is the most deadly. All three arise in the top 0.1 millimeter thick layer of skin, the epidermis. Basal cell carcinomas arise in the bottom cell layer, which regulates the supply of new skin cells. Melanoma forms from derailed pigment-forming cells in the same basal layer, the melanocytes. And squamous cell carcinoma starts in the layer above.
Protecting the skin against an overdose of UV radiation is important, according to both De Gruijl and Sigurdsson. But a nuanced view on lubrication also offers scope for the effects of UV light that we do want. For starters, it makes the epidermis thicker and tanner, making it more resistant to UV rays. Pigment-forming cells make melanin, which surrounds the nucleus of skin cells and absorbs the energy of UV radiation before it can damage the DNA. And other cells in the epidermis divide faster, thickening it and protecting the underlying dermis from aging UVA rays. “It is wise to let the skin gradually get used to the sun after the winter,” says De Gruijl. “People with an outdoor occupation run slightly less risk of melanoma than the average population. Because of their used skin, they burn less quickly. ”
“On our latitude, you don’t burn so easily with your daily trade and walk,” says De Gruijl. “If you have an office job and you take a daily lunch walk at lunchtime, then I would not slather.”
Also read: Skin ‘sees’ sunlight and turns brown
Sigurdsson is chairman of a working group that formulated a position for the Dutch Society for Dermatology and Venereology last year. It is striking that it also includes the nuanced message about habituation. “Habituation offers considerable protection,” he says. “We know that from people who get a light treatment for their sun allergy. They are exposed to UVB radiation for a few seconds a few times a week in the spring for four to six weeks. After that treatment their skin is more resistant to the radiation in the summer. ”
But this used skin does not fully protect. That is why he advises to always use sunscreen on tanned skin: at least factor 15, preferably factor 30.
A second effect of UV-B radiation: it stimulates the production of vitamin D. The skin is the most important source of that vitamin for our body. Under the influence of UVB radiation, a molecular ring of the substance 7-dehydrocholesterol breaks open in the walls of skin cells. This creates a precursor to vitamin D3. The heat from the skin converts it into vitamin D3. This is converted into an active hormone in the liver and then in the kidneys.
Brittle bones and weak muscles
Vitamin D is essential for the calcium balance in the body. Deficiency in children leads to rickets: a disease with bone growth, brittle bones, weak muscles and poorly developed teeth. Also in the elderly, a deficiency of vitamin D can eventually lead to osteoporosis and muscle weakness. Vitamin D is naturally found in fatty fish and some mushrooms.
If you block UVB exposure, you block the production of vitamin D. How much vitamin D do people need? That question leads to discord, says De Gruijl. “The Health Council is reluctant.” Fifteen minutes a day with hands, face and preferably bare forearms in the summer sun would be enough. “But in winter we collectively go through a vitamin D dip,” says De Gruijl. Some scientists think this is bad for public health.
There are indications of numerous beneficial effects of vitamin D. It is said to strengthen the immune system, protect against diabetes by controlling blood sugars, against cardiovascular disease thanks to its antihypertensive effect, and even against Alzheimer’s and multiple sclerosis. It may also protect against colon cancer and various other cancers. “Advocates of the anti-cancer effects want to see the blood level as much as two or three times higher.”
De Gruijl showed that people who had too low a vitamin D level in the winter ran a higher risk of colon cancer. “There is a link, but it has not yet been shown that the higher risk of colon cancer is due to vitamin D deficiency. But in mice that spontaneously develop colon cancer, we saw that those tumors grow less quickly if they were given vitamin D or UVB radiation. ”
Trials in sick people given vitamin D show no apparent effect on any disease, French researchers concluded in a 2014 review article reviewing hundreds of studies.
As thick as peanut butter
“So there is still insufficient evidence for the positive effects of vitamin D,” says dermatologist Nerkingen from Rotterdam. In addition, the fear that people who faithfully apply sunscreen will not make enough vitamin D is also unfounded. Especially since most people don’t get the required amount of sunscreen to use. It must be as thick as a layer of peanut butter on a sandwich, writes the NVDV. “But nobody does that,” says Nlijst.
In addition to the positive influence on skin thickness and vitamin D production, UV radiation has other effects. It increases the amount of nitric oxide (NO) in the skin, which can lower blood pressure. It relieves skin diseases such as psoriasis and eczema.
To stop the surge in skin cancer, the message must be clear
Tamar Nijsten dermatologist
And perhaps the most appreciated effect: it makes people happy and feels good. This could be because UV radiation stimulates the production of a molecule with an opium-like effect, beta-endorphins. Some studies show that this substance increases in the blood after exposure to UV radiation, in sufficient quantities to reach the brain, but several others do not.
“There is still a lot unknown. But if we put too much emphasis on the adverse effects of sunlight, we completely lose sight of the beneficial effects ”, says De Gruijl.
Dermatologist Nerkingen from Rotterdam does not agree. There is no room for nuance, people just have to smear, he thinks. “To stop the surge in skin cancer, the message must be clear.”
Nijsters hopes that people will get tanned and consider baking for hours to be dirty and unhealthy. “Someone with a tanned skin is still seen as vital and sexy. Whoever tans has had the best holiday. We have to get rid of that. ”
A version of this article also appeared in NRC Handelsblad of 8 August 2020
A version of this article also appeared in nrc.next on August 8, 2020