A study funded by the SNSF shows that in winter weak sunlight prevents the Swiss population from producing sufficient levels of vitamin D.
Too much sun increases the risk of skin cancer. But moderate exposure is needed to produce vitamin D. This substance is essential for bone health and may also play a role in preventing respiratory infections, autoimmune diseases and certain types of cancer.
A new study shows that in Switzerland, between the end of the autumn and the beginning of spring, sunlight does not even come close to providing the daily dose of 0.024 milligrams of vitamin D recommended by the organization World Health Organization (WHO). The study was supported by the Swiss National Science Foundation (SNSF) and was published in the Journal of Exposure Science and Environmental Epidemiology.
The researchers measured the intensity of solar UV irradiation in Switzerland for a year and used the resulting data to create a computer simulation. The simulation allowed a precise estimate of the impact of sunlight on the production of vitamin D and the risks of sunburn.
Winter is problematic
In summer synthesizing vitamin D is simple: at noon, a person wearing a shirt (22% of uncovered skin) takes only 10-15 minutes to produce the recommended daily dose. But sunburn may occur about ten minutes later, which increases the risk of developing skin cancer.
In winter, the situation is different. In general, less skin – about 8%, which represents the face and hands – is left uncovered. Furthermore, the solar UV radiation is weaker due to the greater distance the rays must travel through the atmosphere. In these circumstances, it takes at least six and a half hours of exposure to produce the recommended dose of vitamin D. Not only is this exposure difficult to achieve, but sunburn occurs before the daily dose is reached. "This is due both to the spectral characteristics of winter radiation and its concentration on small areas of the skin," says David Vernez, project leader and risk estimator at the Center for Primary Care and Public Health (Unisanté) in Lausanne. "Fortunately, it's not all that easy to do."
The big surprise of this study was the marked difference between summer and winter. "In Switzerland, it is practically impossible to produce enough vitamin D to get the recommendations of the WHO in every season," says Vernez. Even with less conservative recommendations, the odds are contrary.
Computer simulations and field data
To achieve their results, the team brought together specialists in public health, meteorology, IT and nutrition to create a simulation of solar exposure. In particular, the algorithms are able to predict the amount of vitamin D produced and to estimate the risks of sunburn for the two most common types of skin in Switzerland.
The computer model uses as input data on sunlight collected in four meteorological stations that represent the different environments of the country during the whole year. To more accurately estimate the amount of UV irradiation in Switzerland, the researchers also used ozone measurements from the EOS Aura satellite operated by NASA.
This work confirmed the environmental origin of the seasonal vitamin D deficiency observed in the Swiss population. But many questions remain, such as daily recommendations, which can vary up to 100%, and the importance of food supplements. "For now, our main recommendation is to avoid solariums in winter," says Vernez. "The risk of skin cancer far outweighs any possible benefit."
. (tagToTranslate) Vitamin (t) Vitamin D (t) Bone (t) Bone health (t) Cancer (t) Epidemiology (t) Public health (t) Respiratory (t) Skin (t) Skin cancer (t) Sunburn