BY RICHARD HOBDAY, PHD

Western literature is filled with references to sunlight and its capacity to lift the spirits. Writers, especially poets, have long commented on this. Yet it is only since the 1980s that the link between light deprivation and depressive illness has been scientifically proven.

The numbers bear this out. The intensity of illumination outdoors is several orders of magnitude greater than that provided by artificial lighting.

In modern buildings, electric lights provide somewhere between 150 and 600 lux, a measure of light intensity, while outside at noon, sunshine can deliver 100,000 lux.

A 1996 study in the Journal of Affective Disorders found that clinically depressed patients in sunny hospital rooms were discharged more quickly than those in darker rooms, an effect that artificial light alone could not replicate.

The sun’s daily cycle of light and dark regulates many of the body’s most important hormonal and biochemical processes. It is our external timekeeper, keeping our internal biological clock running smoothly.

When light enters the eye and stimulates the retina, two things happen. First, nerve impulses travel along the optic nerve to the part of the brain that interprets what we see.

At the same time, impulses pass to the hypothalamus, a gland that secretes serotonin, a hormone that plays a key role in controlling moods and regulating sleep patterns, body temperature, digestion, and sex drive.

Research suggests that in people with seasonal affective disorder (SAD), the hypothalamus responds differently to light, a disruption that bright light can help correct. Serotonin levels fall during the winter months, and low serotonin has been linked to anxiety and depression.

One of serotonin’s functions is to suppress melatonin, produced by the pineal gland. When light levels fall, serotonin declines and the pineal gland secretes melatonin into the bloodstream, inducing sleep by depressing activity in the brain and slowing other physiological processes.

Winter Blues and Light Hunger

As many as 20 percent of adults may suffer from a mild form of depression during the winter months, the so-called “winter blues.” Modern lifestyles appear to be a contributing factor, giving rise to a related condition known as light hunger.

Niels Finsen, MD (1860–1904), the great light therapist and Nobel Laureate, described it from personal experience in an interview the year before he died, in 1903: “All that I have accomplished in my experiments with light and all that I have learned about its therapeutic value has come because I needed the Light so much myself. I longed for it so.”

Many people share that longing, most visibly at sunny vacation resorts, where the impulse to bake in the midday sun may reflect the body’s drive to recover lost sunlight. Even for those who don’t normally sunbathe, spending an hour outdoors each day year-round makes a meaningful difference to psychological well-being.

There is a striking irony in all of this. People spend so much time indoors that they invest in light-boxes and dawn simulators to compensate for the lack of sunlight, and yet they are simultaneously discouraged from going outside at all.

The connection to sunbathing may be closer than it appears: vitamin D deficiency is itself a recognized cause of depression, and it has been suggested that the seasonal pattern of SAD may reflect changes in vitamin D3 levels, which in turn affect serotonin. If so, light therapy for SAD may simply be compensating for low serotonin brought on by insufficient sun exposure during the summer months.

Sunlight Therapy in the Ancient World

Sunlight has been used as a medicine for thousands of years. The ancient Greeks referred to sunbathing as heliosis, after their sun god Helios, and also took sand baths in the sun, which they called arenation.

The Romans were great believers in the healing powers of the sun’s rays, and they also practiced what we would now call preventive medicine. The Roman scholar Pliny the Elder (AD 23–79), who was a fierce critic of the doctors of his day, described sunbathing as “the best of all self-administered remedies” and sunbathed daily after a light lunch and before a cold bath.

With the fall of Rome and the rise of Christianity, sunlight therapy fell from favor. In Rome, as in Greece, heliotherapy was closely linked with sun-worship. The early Christians had fought a long, bitter campaign against pagan solar cults and, once their church had become established, they wasted no time in eliminating overt sun worship in all its forms.

Unfortunately, knowledge of the sun’s healing powers seems to have disappeared from the collective consciousness around the same time. The Dark Ages spelled the end of sunlight therapy in Europe for over a thousand years.

Sunlight Under the Microscope

In 1877, two British scientists, Arthur Downes, MD, and Thomas Blunt, discovered that sunlight had a pronounced bactericidal effect, which they reported in the Proceedings of the Royal Society.

Their experiments showed that test tubes exposed to sunlight remained clear of bacteria, while covered tubes became cloudy and teeming with microorganisms. Sunlight, they concluded, was a potent lethal agent, even through glass.

In 1890, Robert Koch, MD (18431910), showed that sunlight was lethal to the bacteria that caused tuberculosis, work that earned him the Nobel Prize for Medicine in 1905. The Prize two years earlier had gone to Finsen, whose groundbreaking research made him the first physician to both use sunlight as a medicine and investigate its effects scientifically.

The Surgeon Who Let in the Sun

Inspired by the success of Finsen, Oskar Bernhard, MD (1861–1939), working as surgeon-in-chief at the Oberengadin District Hospital in Samaden, Switzerland, began using sunlight to heal first wounds, then tuberculosis.

On the night of February 2, 1902, an Italian was brought to the hospital with severe knife wounds. Eight days later, the operation wound burst open, and gaped widely, with only a few stitches holding. An attempt to re-stitch the wound failed as the edges could not be brought together again.

The wound was slow to granulate (the first step in the healing process, in which red, moist tissue develops on the surface of an open wound or ulcer) and discharged profusely. None of the treatments used to dry it up had any effect, so Bernhard took the unusual step, at that time, of exposing the wound to the sun:

As I entered the hospital one beautiful morning, and the sun shone warmly through the open window, while a refreshing and stimulating atmosphere filled the whole ward, the thought suddenly occurred to me of exposing this large wound to the sun and air; for the mountain peasants of the Grisons also expose fresh pieces of flesh to the sun and dry air to preserve them, and in this way makes a nourishing and tasty food, the well-known “Bündnerfleisch”.

So I resolved to try this antiseptic and drying effect of the sunlight and air on the living tissues. Then, to the astonishment of the staff, I had the bed put to the open window and laid the large wound open. By the end of the first hour and a half of exposure, there was a marked improvement, and the wound presented quite a different appearance. The granulations became visibly more normal and healthy, and the enormous wound skinned over quickly under the treatment.

This success led him to treat all granulating and infective wounds with sunlight. The treatment took place either in the open air on a veranda or in the sick ward, and the procedure was to remove the dressings and expose wounds to the sun for several hours daily.

Bernhard observed that, when exposed to sunlight, torpid wounds became clean and dry, the granulations smaller and fresher. Discharging ulcers and pockets, which would normally have required frequent dressing changes, and even then often continued to discharge, dried up under the treatment, and the discharge from badly smelling wounds rapidly became odorless.

When treating compound fractures, Bernhard also found that sunlight stimulated the formation of callus, the new tissue that forms around the ends of a broken bone, and that it had a marked analgesic effect.

The Art of the Sun Bath

During the Great War, Bernhard gained a reputation for conserving severely injured limbs that would normally have been amputated by other surgeons, and for never losing a patient to tetanus or gangrene.

His success with sunlight brought national and international recognition, but the physician who popularized heliotherapy as a remedy for war wounds and tuberculosis was Auguste Rollier, MD (1874–1954), who began to use sunlight on his patients at a clinic in Leysin, Switzerland, in 1903, one year after Bernhard.

It was at Leysin that Rollier pioneered a form of treatment for surgical tuberculosis in which very slow tanning in cool conditions was combined with rest, fresh air, nourishment, and exercise.

Rollier’s method of using sunlight was copied by doctors in Switzerland, the United States, and other countries around the world and, over a period of forty years, became the standard procedure in a number of hospitals worldwide.

Drop by Drop: Rollier’s Method

Gradual exposure to cold air stimulated the body to produce heat, and this sped up the healing process. Cool conditions also reduced the risk of over-exposure to the sun’s rays. Auguste Rollier regarded exposure to the sun at temperatures greater than 18°C, or 64°F, to be a “hot-air bath” and not a sun bath.

As he put it in the British Medical Journal in 1922: “A very current mistake consists in thinking that the sun bath is all the more efficacious if prolonged or taken when the sun is at its hottest; this is an inconsistency against which Nature seems to warn us.”

Rollier considered that the safest way to sunbathe was to begin with the feet, then the legs and arms, before exposing the abdomen and chest.

Rollier’s success with heliotherapy can be attributed to the way in which the dosage of sunlight was scrupulously graded according to the response and requirements of each patient. The caution with which he approached exposure of the upper body to sunlight was a particular characteristic. He believed that the sun should be dispensed “drop by drop” when nearing the chest.

What is clear from the many articles, books, and scientific papers Rollier published over a forty-year period is that he and his staff at Leysin were able to transform weak, sickly, tubercular patients into strong, deeply tanned individuals who were free of the disease. Auguste Rollier practiced sunlight therapy at Leysin from 1903 until well into the 1940s and had thirty-six clinics with a total of more than a thousand beds.

Three Victories, One Silence

The heliotherapy practiced by Oskar Bernhard, Auguste Rollier, and others enjoyed three major successes: the cure and prevention of rickets; the treatment of extrapulmonary tuberculosis; and the disinfection and healing of wounds.

While sunlight played a large part in this, it was only one factor and not the whole of the regimen. Exposure to pure air, freedom from fog, smoke, and dust, combined with good nutrition, prolonged rest, and orthopedic treatment, all played their part.

Nevertheless, the mistaken belief that sunlight alone could cure tuberculosis was widely held during the 1930s. It was not uncommon for someone with advanced tuberculosis of the lungs to expose the entire surface of their body, the chest included, to a combination of strong sunlight and hot, humid air, with disastrous consequences.

As relatively few physicians made regular use of heliotherapy and there was little incentive for those who did not to become familiar with its basic principles, there was ample room for error.

There was also outright opposition. When Rollier presented his first results in Paris in 1905, it is said that the entire audience walked out. Forty years later, the distinguished cancer specialist John Lockhart-Mummery dismissed sunlight therapy in his book Nothing New Under the Sun: “Sunlight and ultraviolet rays are very popular just now as forms of medical treatment, but except for a very limited field, they come rather under the head of pseudo-magic than scientific treatment.”

Against this background, it becomes a little clearer why the negative effects of exposure have been so widely publicized, and why the beneficial effects of sunlight on cancer and other diseases have received so little attention.

Modern sun-avoidance campaigns address only half the picture. The physicians who came before antibiotics knew the other half, and they practiced it with remarkable results.

Sunlight is not simply a risk to be managed. In the right conditions, at the right time, and in the right dose, it remains what it has always been: a medicine. Spring and early summer may be especially valuable times to receive its full benefits, as generations before us once understood.

Our ancestors had to attune themselves to the sun’s natural cycles in order to survive. Our physiological and psychological requirements are much the same as theirs.

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Richard Hobday, PhD, is an internationally recognized researcher and author. He has many years of experience in solar building design and is a leading authority on the history of sunlight therapy.

Well Being Journal adapted the above excerpt from The Healing Power of the Sun by Richard Hobday, PhD. Copyright © 2021 Findhorn Press. Printed with permission from the publisher Inner Traditions International. www.InnerTraditions.com