Let’s Give Sunlight Some Credit for Health Benefits

 We have so often been warned about the nasty ultraviolet (UV) radiation the sun sends our way and its potential to cause skin cancers that some act as if any exposure to sunlight is risky.  However, evolution seems to be telling us that too little exposure to the sun can be unhealthy as well.  Humans emerged from Africa with dark skin designed to limit the damage from UV in the African environment.  As people spread out into more moderate climates they tended to develop lighter complexions.  If all UV exposure was bad, one would expect the dark skin to be maintained.  Instead, as lesser sunlight intensities were encountered evolution apparently decided to lighten skin color in order to experience higher UV exposures.  The Economist provides some emerging data that suggests that limiting exposure to sunlight is not necessarily a good idea.  Data has begun to show that those who do not experience the proper amount of sunlight have higher mortality rates than those who do. The argument is presented in The health benefits of sunlight may outweigh the risk of skin cancer.

It is well established that sunlight on the skin produces essential vitamin D.  We may not worry about this vitamin enough because it is so available in supplement form.  However, the effectiveness of supplements is being called into question.

“UV radiation is necessary for the body to make vitamin D, a lack of which can cause soft bones and skeletal deformities in children. Higher levels of vitamin D in the blood are associated with all sorts of potential health benefits, from better heart health to lower cancer risk. But several big studies into the effects of vitamin D supplements have had disappointing results, says Amaya Virós, a skin-cancer researcher at the University of Manchester. (In 2022 an editorial in the New England Journal of Medicine argued that, given those findings, doctors should stop recommending their patients take them for general use.)” 

The closer researchers look at the effect of sunlight on skin the greater the benefits seem to be.

“There is no shortage of candidates: sunlight seems to affect the expression of many different genes. One mechanism that has attracted particular attention involves nitric oxide, a signalling molecule that, among other things, relaxes blood vessels and lowers blood pressure. In 2009 a group of researchers based in Germany showed that UV irradiation converts chemicals in the skin into nitric oxide, which then makes its way into the blood—and that whole-body exposure caused a quick and substantial drop in blood pressure.”

“That throws suggestive light on existing data showing that blood pressure tends to rise the farther from the equator you go. One 2017 paper found an increase of roughly 5mm of mercury (the units in which blood pressure is measured) for every thousand kilometres north of the equator. High blood pressure is a risk factor for heart disease—and death rates from heart disease in high-latitude countries also show a striking seasonal pattern, being highest in winter and lowest in summer.... Some of that is down to colder weather, changes in diet and the like. But some researchers wonder if at least some of it could be down to lack of sun, too.”

“Another intriguing line of evidence concerns UV radiation’s effects on the immune system. For multiple sclerosis (MS), it appears to offer relief (like high blood pressure, MS seems to be more common in higher latitudes). Some scientists are exploring whether UV’s effects on the immune system might also improve its ability to combat cancers.”

Let us also recognize the epidemic of myopia that is thought to originate from a lack of bright sunlight that our children’s eyes need to experience outdoors.

“A lack of sunlight is thought to be an important reason why, in some Asian cities, more than 80% of teenagers now need glasses. Bright light—of the sort that is hard to generate indoors—appears vital to regulate the growth of children’s eyes.”

These results may be just the first few drops in the bucket.  Other studies indicate that health benefits from sunlight exposure are quite broad with a definite effect on mortality rates.

“These include protections against heart disease, cancer and autoimmune diseases. A study published last year, for instance, examined medical data from 360,000 light-skinned Brits and found that greater exposure to UV radiation—either from living in Britain’s sunnier southern bits rather than the darker north, or from regularly using sunbeds—was correlated with either a 12% and 15% lower risk, respectively, of dying, even when the raised risk of skin cancer was taken into account.”

“That fits with the results of another big study published a decade earlier. Led by Pelle Lindqvist, an epidemiologist at the Karolinska Institute in Stockholm, it followed 30,000 Swedish women for 20 years. It likewise found that, even after correcting for things like age, wealth and health, sun-seeking behaviour was associated with a lower chance of death from all causes. People with the most sun exposure had only half the risk of dying compared with those who had the least exposure.”

These findings suggest we have been poorly served by the focus on skin cancer.  The following seems somewhat better advice.

“’The big picture is that the benefits of sunlight outweigh the risks—provided you don’t get sunburnt,’ argues Richard Weller, a dermatologist at the University of Edinburgh and one of the authors of the British study.”