Sunlight Health Benefits Beyond Vitamin D
In the 1920s, battlefield surgeons observed that soldiers with open wounds healed faster when their bandages were left off and sunlight reached the raw tissue. Patients with stiff, painful joints reported their arthritis eased after sitting in the sun. People with rattling coughs from bronchitis and lung infections found their symptoms subsided. Hypertensive patients saw their blood pressure drop. None of this fit the emerging model that sunlight was dangerous.
The Lancet, one of the world’s oldest and most respected medical journals, declared sun exposure “one of nature’s greatest aids to maintaining and acquiring proper health.” In 1932, the journal published an article calling for more public spaces where people could strip off. “On first consideration, the idea of a community of people deliberately practising nudity, especially with municipal encouragement, strikes the average person as somewhat ridiculous,” that article read. “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.”
Today, the model has flipped completely. Public health authorities tell people to cover up and apply sunscreen even in winter. The message drilled into children since the 1980s is that the sun is the primary cause of skin cancer and that zero unprotected exposure is the only safe amount. Journalist Rowan Jacobsen, author of the new book “In Defense of Sunlight,” says he grew up with that message. Then he learned that sun exposure triggers mood-boosting endorphins — the brain’s own pleasure chemicals. “If we’re wired to seek out sunlight, there must be a reason,” Jacobsen writes.
The brain’s pleasure system can prime humans to seek out things that are unhealthy — drugs, alcohol, sugar. Jacobsen acknowledges this objection. But he builds a case that moderate sun exposure does more than feel good. It changes the body in measurable ways that reduce disease risk. The data that do not fit the current model come from multiple independent laboratories.
Vitamin D Was Only the Beginning
The most famous benefit of sunlight was always vitamin D. The skin produces this chemical when struck by UV rays. Correlational studies showed that people with high vitamin D levels had lower risk of obesity, diabetes, osteoporosis, heart attack, stroke, depression, respiratory infections, and colorectal cancer. The logic seemed straightforward: sunlight makes vitamin D, vitamin D protects against disease.
But the model broke when researchers tested it directly. Dietary supplements of vitamin D, Jacobsen notes, have largely failed to produce the same health benefits. The only exception is in people with severe deficiency. For everyone else, swallowing vitamin D pills did not lower their risk of heart disease, cancer, or depression the way high natural vitamin D levels predicted.
This leaves an intriguing possibility. Measurements of people’s natural vitamin D levels may have been acting as a proxy for something else — their total sun exposure. Sunlight might protect the body through multiple mechanisms, not just one. Vitamin D was the first pathway discovered, but it may not be the most important.
One likely alternative pathway involves nitric oxide. This is a tiny chemical molecule that causes blood vessels to dilate. When blood vessels widen, blood pressure drops. Scientists have recently concluded that nitric oxide deficiency is a major driver of hypertension — chronically high blood pressure that damages arteries and the heart.
A series of studies found that exposure to UV light releases nitric oxide in the skin. From there, it enters the bloodstream and relaxes the cardiovascular system. Jacobsen points to this finding as one reason people in Mediterranean countries tend to have such good health. The leafy vegetables in the region’s famous diet contain lots of nitrates — the raw material for nitric oxide. But plentiful sunlight in those areas helps the body convert those nitrates into active nitric oxide.
Just adopting a Mediterranean diet lowers blood pressure. But adopting the diet while also increasing sun exposure lowers it more. “It’s the combination of the two that does the trick and should be the foundation of a true Mediterranean diet,” Jacobsen writes.
The Immune System Needs a Sunlit Governor
Moderate sun exposure does something else that researchers are only beginning to understand. It releases chemicals in the skin that help rein in an overactive immune system. This matters because many chronic diseases involve the immune system attacking the body’s own tissues.
Multiple sclerosis is one such disease. The immune system attacks the protective coating around nerves. Sun exposure appears to soothe this condition independently of vitamin D production. The mechanism involves immune-regulating cells that are activated by UV light reaching the skin.
Type 1 diabetes is another autoimmune disease where the immune system destroys insulin-producing cells in the pancreas. Evidence suggests sunlight exposure may reduce the risk of developing this condition. Again, the effect appears separate from vitamin D.
The infrared wavelengths in sunlight can penetrate deep into the body. These longer wavelengths stimulate mitochondria — the power plants inside cells. Improved mitochondrial function means better metabolism, more efficient energy use, and less cellular damage. This is not a theory. It is a measured effect that has been replicated in laboratories.
The dark cloud over all this is skin cancer. Jacobsen does not deny that sun exposure increases skin cancer risk. He points out that most skin cancers are basal cell carcinomas and squamous cell carcinomas. These types rarely spread to other parts of the body and are typically treatable with surgery.
Melanoma is more dangerous. It spreads quickly and can be fatal. But it is relatively rare compared to other cancers. The survival rate for melanoma is still very high when caught early. “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 cancer,” Jacobsen writes. “And I think we need to find the risk-benefit ratio.”
An influential study of 30,000 Swedish women supports this calculation. Over a 20-year period, women who avoided the sun were about twice as likely to die as women who got regular sun exposure. The study controlled for other factors. The finding held. Sun avoiders died younger, and the cause was not skin cancer — it was heart disease and other conditions that sunlight appears to protect against.
The balance of risks depends on skin tone, season, and latitude. There is no single recommendation for optimum sun exposure that fits everyone. Jacobsen’s advice ends up close to what UK health services already recommend: make the most of mornings and evenings when UV levels are lower, cover up and find shade during the hottest times of day, avoid burning at all costs. Even short periods of exposure may be enough to glean the benefits.
The message is simple. “Get sun. Not too much. Go outside.”