Yet the ever-rising number of covid-19 cases and deaths has revealed that the sun is no match for this new virus.

Trump is not the first to expect summer to bring medical miracles. Belief in the sun’s healing power is ancient, and while that faith seems rooted in sentiment rather than science, modern biomedicine has provided ample specific instances of how sunlight can deliver health benefits — from vitamin D to disinfection. Our efforts to exploit those benefits are not miraculous, but reflect science at work in its plodding, imperfect way. And so, while ultraviolet light has been some use in the fight against covid-19, deployed as a disinfectant on surfaces or in the air, sunlight is not the magic bullet that will end the pandemic.

Before the rise of modern biomedicine, many Americans embraced an emotional connection to the curative powers of the sun. “All the instincts of human nature,” one mid-19th-century writer asserted, “accept the idea of the healthfulness of light, and its agency in strengthening and cheering human life.”

But this embrace wasn’t a rejection of science: The same writer demonstrated her familiarity with the new science of electromagnetic waves, expressing wonder at the “five hundred millions of millions of vibrations a second” sunlight excited in the air. But her scientific claims rested on the old idea of the power of the sun to dispel miasmas — the bad smells caused by putrefying matter that resulted in disease. Sunlight, she assured readers, would cleanse those odors and banish disease, “whenever it rests on what is offensive or unclean, it is only to purify it by its chemical and subtle influences.”

This claim was based in experts’ understanding that unhealthy environments produced disease. This notion was correct even if their miasmatic theory was not. In reality, it would be clean water supplies, sewage treatment and swamp drainage that lowered rates of disease and death.

But this didn’t shatter the faith Americans held in the sun. Belief in the healthfulness of sunlight spurred public housing laws in many cities that regulated building height and density, set minimum standards for natural light and ventilation in apartment buildings and brought parks, sun-centered sanitariums and outdoor recreation programs. And all of these reforms made people healthier.

The rise of Germ Theory, far from banishing the sun from public health practice, offered new scientific support for sunlight’s health benefits, including its power as a disinfectant. Physician and celebrity health promoter John Harvey Kellogg was a dedicated heliophile, but also an early convert to Germ Theory. He incorporated the study of gut bacteria into his sometimes obsessive interest in keeping the bowels clean. Yet, knowledge of germs did not replace his love of light: he extolled its “tonic, vitalizing, energizing influence” whose effects “sometimes seem little short of miraculous.” What Kellogg deemed a wondrous power would subsequently be applied in modern disinfection tools employing ultraviolet radiation.

The discovery of vitamin D provided a second example of a modern science lending support for the healing power of the sun. Rickets, a metabolic disorder causing the softening of bones in young children, reached epidemic proportions in the darkening cities of Europe and America in the 19th century, affecting upward of 50 percent of urban children. By the 1920s, when vitamin D was discovered, health researchers had already established that adequate sunshine or regular doses of cod liver could prevent or cure rickets. Vitamin D, it turned out, gave cod liver oil its anti-rickets power; it was the link between sunshine, diet and strong bones.

Natural sunlight was free, but often inaccessible in the crowded and polluted modern city. Science and industry answered the need with new “sunshine” products. And the efforts to promote these products harked back to some of the earlier emotional claims about light and health. In 1928, Metropolitan Life Insurance gave its policyholders “Sunlight the Health Giver,” a colorful pamphlet that explained “the sun has the power to cure and make healthy.” Infant care manuals instructed mothers to make sure their babies developed a “healthy tan.” Health guides promoted outdoor play in good weather along with tanning.

Those indoors could partake of sun as well. Blindingly bright ultraviolet lamps beamed artificial sunlight on hospital patients, on residents of tuberculosis sanitariums and on thousands of children whose parents bought the promise of the “summer sun … made to shine at the turn of the switch.”

While once a pale complexion was seen as a marker of class and racial privilege, by 1929, Harper’s Bazaar could declare, “If you haven’t a tanned look about you, you aren’t part of the rage of the moment.” Within a few decades a multibillion dollar industry evolved to supply sunbathers with oils and lotions for the perfect glow. Popular belief in health and sunshine, validated by vitamin D and other scientific findings, make it difficult even today for many to heed warnings about the link between tanning and skin cancer.

This enthusiasm for using light to heal helped to launch new medical devices as well, among them quartz crystal speculums and metal prostatic applicators to direct UV light to disinfect the colon, and treat hemorrhoids, or tuberculosis of the larynx. Through the 1930s, doctors in the United States and Europe successfully treated patients with severe bacterial infections by irradiating the patients’ transfused blood with UV light. These technologies never really lit up the medical world and faded into obscurity with the advent of the antibiotic era. Nevertheless, they laid the foundation for the application of ultraviolet light for disinfection, while further establishing the idea that the sun, or its derivatives, promoted health.

In recent decades the link between sunlight and health seems less certain. On the one hand, findings about tanning and skin cancer cast a shadow over both unprotected outdoor tanning and the indoor tanning industry. On the other hand a troubling resurgence of clinical rickets on top of growing concerns with the hidden health costs of low vitamin D levels, highlighted the difficulty of balancing the risks of too much or too little sun exposure.

And now we face the question of how UV light and the outdoors might be part of our response to coronavirus. For example, the New York MTA is running a pilot program to add UV disinfection to its regimen of subway cleaning; restaurants and other public spaces are incorporating powerful UV lights into their heating and ventilation systems to kill airborne virus particles before they can spread to patrons through recirculated air.

What this summer has shown is that sunlight, in the form of UV rays, can play a role in reducing covid-19 on surfaces and in the air. But it has not, as some elected officials hoped, brought an end to the current pandemic. The complicated history of the science of sunlight reminds us about the dangers of allowing hope and faith to supplant science. Only vigorous advocacy for science-driven public health practices will help us conquer the challenge of covid-19.



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