Our skin has with the sun (and its UV radiation) relationships that are sometimes happy, sometimes dangerous, always complex and never harmless. Jean-François Doré, a researcher in the French National Institute for Medical Research, has lectured on the current scientific knowledge, during the 5th meeting of the French Society of Anti-oxidants, held in Paris on 15 November 2012. A lecture full with contrasts …
An emeritus Director of Research in Inserm, in the Lyon Cancer Research Center, Jean-François Doré has, for a long time, studied the effects of sun on our skins, from the answer of the human melanocytes to UV radiation to how using sunscreens may impact our ways of exposure to sun.
Just for once, he said, he began his conference by detailing the benefits we get from sun … which did not prevent him to point out all of its less positive effects.
When the sun is friendly
A fact is unquestionable: the sun is essential for life on the Earth.
Being exposed to sunrays is highly beneficial to the human health.
Good for our morale
Sun has a direct effect on our mood. Not only, because we think, a sunny weather is more agreeable than a rainy greyness, but also because an exposure to UV radiation modifies our physiology, by releasing endorphins.
Endorphins have been discovered in the seventies. Their name comes from “endogenous”, meaning something that is in our body, and “morphine”. These “natural morphines” are, indeed, neurotransmitters released by our brain in psychological or physical stresses situations (efforts, or high-intensity emotions). They link to the brain opiate receptors, and provide an analgesic and euphoriant effect. Less pain, more happiness: endorphins are also called the well-being hormones.
Among the situations that produce most of the endorphins: run a marathon, have sex, exposure to sun … Or, more rightly, to its UV radiation. In fact, if beaches may be seen as, after Jean-François Doré’s words, “legal immense shoot galleries”, tanning booths have exactly the same effect.
Good for vitamin D
The “vitamin D” is, in fact, a steroid hormone whose the main function is to balance the phosphocalcic metabolism: it is a factor in the absorption of calcium and phosphorus by intestines, as well as in their reuptake by kidneys.
Vitamin D deficiency leads to rickets in children, and to osteomalacia (defective bone mineralization) in adults.
However, vitamin D has also a role in the functioning of something as 200 genes, hence, its importance in some diseases (diabetes, cancers …)
Skin exposure to sun synthesizes 80 to 90% of the vitamin D we need. UVB radiation induces the manufacturing of the provitamin D3, which is, then, isomerised in vitamin D3 and transported in the overall body for many uses.
Good to fight melanomes?
This may seem paradoxical, but there are, nowadays, arguments that make it possible to think that, even for melanomas (skin cancers) due to sun exposure, this same exposure may also be linked to a better prognosis and to a lower mortality rate.
For instance, some studies have shown that the mortality rate is lower for melanomas diagnosed in summer (when more exposed to UV) than for those diagnosed in winter. A possible role of vitamin D is thought of. Nevertheless, the mechanisms involved in these protective effects are not yet established.
For Jean-François Doré, this hypothesis is not at all enough to continue questioning policies of sun protection, by the name of vitamin D, be it by extending exposures to sunrays, or by using artificial UV radiation in tanning booths.
“A potential lack of vitamin D, and deficiencies, nowadays, are extremely rare,” he says, "shall be compensated for through food, fatty fish being at the top of the list."
Indeed, sun exposure is always an aggression towards the human species. Ensuing damages are often irreversible.
When sun is harmful
Sun rays are especially aggressive towards two of our organs: eyes and skin.
For our eyes, it is a known source of two diseases.
• Cataract: it is emphasized by the UVB, and even “standard” sunglasses cannot fully protect the eyes. Only the goggles with side-shields offer the right protection.
• Age-related macular degeneration: it could be induced by exposure to blue light. Jean-François Doré warns against the development of LEDs. The white light they produce is, in fact, a blend of yellow and blue radiations…
The effects on our skins
On skins, UV radiation (be it from sun or from artificial sources) has many effects, spread in time.
• The positive immediate effects
> Due to the UVB effect, tanning and epidermis thickening are a skin’s defensive reaction. > UVB radiation induces also the synthesis of the vitamin D.
• The negative immediate effects
> UVB radiation is a cause of erythema (sun burns).
> Sun exposure leads to immunosuppression (impaired immune responses.)
• Long-term negative effects
> Along the time and repeated exposures, pigmented lesions may appear: age pigments, lentigines, naevi…
> UVA radiation is a cause for the speeding up of cutaneous ageing.
> UV radiation is a factor for cancers: basal- and squamous-cell carcinoma, melanomas…
The skin’s defenses
The human species has developed specific responses systems against the sun UV radiation. They are as many ways of protection against its harmful effects.
• The epidermis thickening. This is probably the most efficient protection. For instance, it has been reported that people who are very often exposed to sun (outdoor workers…), who have “built” a thicker skin, develop fewer melanomas than people who are intermittently exposed (vacationers exposed three weeks a year…).
• Tanning. The lower layer of the human epidermis contains melanocytes, cells that produce a black dye, melanin. When exposed to sun, the melanin synthesis is activated, and melanin is, then, transferred to the keratinocytes, in the upper skin’s layers. The ensuing dyeing of the skin, tan, is a weapon against the UV radiation entering the skin.
However, these defenses are not always enough, especially against the most harmful effects of sun.
Solar elastosis, which is seen as a skin that has lost its suppleness and is marked with deep furrows, may require many years to become seeable. However, its process is on its way since the very first exposure. Under UVA radiation, the number of fibroblasts contained in derma decreases. Bit by bit, their ability to synthesise collagen is impaired, and the elastin fibers they produce are modified.
Solar elastosis comes from degraded elastin being laid in the upper layers of the derma. It is more frequent in chronically exposed areas (head and neck), in fair-skinned people, and increases when ageing.
In fact, it is the answer to the cumulative dose of UV absorbed over the years.
Immunosuppression and cutaneous cancers
Exposure to UV radiation, acute with a high level, or chronic with a low level, induces a local and systemic immunosuppression, following complex mechanisms initiated by several photo sensors on the skin surface (DNA, trans urocanic acid, materials of cells membranes…).
Further, it is recognized as carcinogenic to the human species, leading to non-melanomas cutaneous cancers and to melanomas, less frequent, but far more “harmfull”.
In France, there are about 7,500 cases reported every year, and circa 1,500 related deaths.
Cutaneous cancers depend on several factors. For instance, they are more frequent in fair-skinned people; melanomas are more numerous when the persons have been exposed when children, “At six, the risk is definite,” Jean-François Doré explains, reminding the audience of the warning advice for young children. “They MUST be protected, with clothes, hats or caps, sunglasses, and sunscreen on whichever surface of skin is visible!”
There is obviously a strong relationship between where melanomas appear and the exposed areas.
No doubt in the expert’s mind: there is a true link between our behaviour with the sun and the increase of the number of skin cancers.
It occurs that our behaviours have been strongly modified over the years, and not the right way.
Longing for tanning, the key to devastating effects
For millenniums, from his beginning as a species, until the 1930s, man has protected oneself from sun exposure.
Even still in the 19th century, exposure to sun was avoided, especially if a woman from the upper social classes. The link between sun and cancer was still unknown; the reason was only to keep a pale complexion, a sign of aristocracy.
Then, life behaviours have been modified; holidays in the plain sunlight have developed, and tan became synonymous with well-being, health and social achievement.
Further, between 1925 and 1930, the role of UV radiation for the vitamin D synthesis has been known. Exposure to sun has become very popular. At the same time, the first UV sources used in preventive medicine were placed on the market. Exposure to UV radiation became a public health objective: exposing children to sun was recommended …
It is only during the second half of the 20th century that the link between UV, cancer and skin ageing has been established. Until when, in June 2009, the International Agency for Research on Cancer (IARC) classified UV in the 100 – 400 nm range in the Group 1 of carcinogenic substances and agents to humans.
Artificial UV radiation
This tanning trend, and the benefits linked to UV exposure have had a further consequence: the development of tanning booths and solariums.
Lowly used before 1980, they became very popular during the ’90s. As per a 2006 study, 70% of women, and 50% of people aged from 18 to 50 have already used a solarium at least once in Northern Europe. The trend goes to children and teenagers: eight per cent of the 13 – 19-year-old in Sweden, and 12% in the USA are frequent users.
The results, after an IARC study released in 2006, “We do have supporting evidence of a causal link between artificial UV radiation and skin cancers, especially for exposure prior to 30.”
In such a way that the word “epidemic” has been associated with this phenomenon.
“This kind of exposure being recent, the true effect of solariums on the incidence of melanomas will be measured only in the coming years,” Jean-François Doré explains. He has taken part, in 2012, in a study, “Evaluation of the impact of exposure to the UV radiation provided by artificial tanning equipment on the cutaneous melanoma in France”.
Conclusion: from 566 to 2,288 deaths are likely to occur within the next 30 years if the UV exposure of French people in tanning booths is not changed. “More than the Mediator!” the expert adds. (Mediator is the French name of a molecule, banned in many countries, but accused to have led to up to 2,000 deaths in France.)
He recommends "tougher prevention action to decrease the use of UV only for aesthetics purpose". In California, solariums are forbidden to under 18 people.
Sunscreen protection: a heated debate!
On the other hand, sunscreens are there to increase the skin defenses against the sun harmfulness, aren’t they?
Indeed, Jean-François Doré is very skeptical about their true efficiency.
No study has ever demonstrated any reduction of the risk of non-melanoma cancers when using sunscreens, after his opinion. Neither any has convincingly demonstrated the reduction of the risk of melanoma. Some have even pointed a risk increase!
The problem, for the expert, does not lie in the reality of the protection index or in the quality of the products, but, once again, in the users behaviour.
“When sun exposure is driven by a wish to be tanned or to stay longer under sunlight,” Jean-François Doré explains, using a sunscreen increases the time of exposure by 13% to 39%. Two studies performed with young volunteers have shown that using a high protection index sunscreen increases the time of sun exposure by circa 30 minutes a day.” Hence, UV exposure.
The behaviour of sunscreens users, thus, would deprive them of the performance of the product.
The strength of prevention
Nevertheless, the problem is not that intractable.
As a proof, Jean-François Doré displays the Australian example. For the last 50 years, Australia has always lived with prevention campaigns about the risks linked to sunlight. Sunscreens are sold by a litre to be cheaper; everything is done to ease their use. Australians, well-informed and well educated, do not go on the beach without a cream, and know how to protect their skins.
In Europe, sunscreens are used to allow for longer exposures…
For the expert, it is time to think again about our ways of thinking. As a conclusion, he reminds the audience that UV radiation is the main environment cause of cutaneous cancers and melanomas, tumours that lead to the death of young adults in a disproportionate rate.
In fact, melanoma is the cancer of young people. Some easy-to-take precautions are enough to prevent it from striking.