Sunshine can help with some serious health problems, argues a new book

Shaded beach huts help us avoid getting too much of a good thing: sunlightJUSTIN TALLIS/AFP via Getty Images BookIn Defense of SunlightRowan Jacobsen, Scribner (UK, US) About a hundred years ago, doctors actively encouraged sunbathing. Soldiers’ wounds, first world war surgeons had noticed, healed a lot faster when exposed to solar rays; people with arthritis felt their pain retreating, while those with bronchitis and lung infections found their coughs subsiding. Blood pressure in hypertensive patients dropped.

The Lancet went so far as to declare it “one of nature’s greatest aids to maintaining and acquiring proper health”, and even called for more spaces to strip off in public. Advertisement “On first consideration, the idea of a community of people deliberately practising nudity, especially with municipal encouragement, strikes the average person as somewhat ridiculous,” reads one article from 1932. “But the discovery that the rays of the sun on the skin exert a beneficent effect on health has done something to undermine these prejudices…

as long as they are done for the sake of health and… the sexes are segregated.” Today, we’re far more cautious.

We are told to cover up and apply generous volumes of sunscreen to protect us from the harmful UV rays, even in the winter. But has this advice gone too far? That’s the argument of a fascinating new book, In Defense of Sunlight: The surprising science of sun exposure by journalist Rowan Jacobsen.

He says he was inspired by the finding that sun exposure can trigger mood-boosting endorphins. “Like most people, I’d had it drilled into me since childhood that the sun was… the primary cause of skin cancer, and that the only acceptable amount of its rays that should be allowed to touch my unprotected skin was zero,” he writes.

“But if we’re wired to seek out sunlight, there must be a reason.” Studies found that exposure to UV light releases nitric oxide in our skin, which reduces blood pressure Despite this slightly shaky premise (the brain’s pleasure system can prime us to seek out much that is unhealthy for us, including drugs, alcohol and sugar) Jacobsen builds a thoroughly convincing argument, as he documents the many surprising ways that moderate sun exposure can revitalise our bodies. The most famous benefits of sunlight once appeared to revolve around its role in the body’s production of vitamin D.

Correlational studies suggested that high levels of the chemical seem to reduce the risk of many health problems, including obesity, diabetes, osteoporosis, heart attack, stroke, depression, respiratory infections and colorectal cancer. Yet Jacobsen notes that dietary supplements of the vitamin have largely failed to make an impact on any of these problems, except when someone has a severe deficiency. This leaves the intriguing possibility that measurements of people’s natural vitamin D levels were simply acting as a proxy of their overall sun exposure, which had been protecting the body through multiple other mechanisms.

One likely pathway is nitric oxide, a chemical that causes our blood vessels to dilate. Scientists have recently started to conclude that nitric oxide deficiency is a major driver of hypertension, and – quite remarkably – a series of studies has found that exposure to UV light releases this tiny chemical in our skin, which then reduces blood pressure. The finding, Jacobsen suggests, may offer one more reason why people in Mediterranean countries tend to have such good health.

The leafy veg of the region’s famous diet, he points out, contain lots of nitrates, but plentiful sunlight in those areas helps people’s bodies to convert this into nitric oxide, relaxing their cardiovascular system. Just adopting a Mediterranean diet has been shown to lower blood pressure, but not as much as also increasing sun exposure, writes Jacobsen: “It’s the combination of the two that does the trick and should be the foundation of a true Mediterranean diet.” Elsewhere, he points to evidence that moderate exposure to sunlight releases chemicals in the skin that help rein in an overactive immune system, which may explain why it appears to soothe conditions like multiple sclerosis – independently of vitamin D production– and type 1 diabetes.

There is even evidence that the infrared wavelengths in sunlight, which can penetrate deep into our bodies, can stimulate our mitochondria, improving our metabolism. The dark cloud hanging over all this is, of course, the heightened risk of skin cancer that comes with sun exposure. Here, Jacobsen points out that most skin cancers are basal cell and squamous cell carcinomas, which don’t often spread to other parts of the body and are typically treatable with surgery.

Melanoma is more dangerous, but it is relatively rare and still has a very high survival rate compared with other cancers. “Yes, sunlight is the major alterable risk factor for skin cancer, but deaths from heart disease are a hundred times higher than deaths from skin can