(2025-08-05) Sunlight Might Hold The Key To Treating Autoimmune Diseases

Sunlight Might Hold the Key to Treating Autoimmune Diseases. Every morning Kathy Reagan Young steps out of the shower in her Virginia Beach home, towels off, dons a pair of protective goggles and stands nine inches from a light box the size of a small space heater. Young presses a button, and the box’s bulbs begin to glow a ghostly purple. She briefly bathes her torso in the ultraviolet rays coming from the bulbs, four minutes per side. Then she goes about her day.

That Young can have an ordinary day is remarkable. In 2008 she was diagnosed with multiple sclerosis (MS)

Young, an advocate for MS patients and creator of a popular podcast, has suffered through many such episodes. But things improved with the arrival of her light box.

Ultraviolet (UV) light boxes, which emit only a narrow bandwidth of light that is not linked to skin cancer, have been used for years in the treatment of psoriasis. Young got a prescription from her doctor, and the box was sent to her by a medical-device company called Cytokind that is hoping to expand such use to MS and other autoimmune diseases and was looking for some practical patient feedback. She tried out the device and gave them some pointers: make it smaller and easier to hold because MS often makes your hands go numb, and build in timed reminders to overcome the cog fog. Then, to her surprise, she found that her fatigue disappeared a few months after she started using it.

For years Young had been forced to rest in bed many times a day, but that stopped with what she calls her UV-fueled rebirth.

Her MS Disease Activity (MSDA) score, which rates MS severity based on the levels of key inflammatory molecules in the blood, was a 1 out of 10, the best possible score, and it has stayed low for more than a year

Autoimmune diseases such as MS and type 1 diabetes occur when our natural defenses—our immune systems—viciously turn against our own bodies and organs. These illnesses are estimated to affect more than 350 million people worldwide.

Although only a handful of clinical trials for MS light therapy have been conducted in people, evidence from a number of medical studies now shows that UV light, the highest-energy part of the solar spectrum that reaches Earth’s surface, has a surprising ability to calm an immune system that has bolted out of control. The new studies offer tantalizing hints that UV therapy might also work for other autoimmune diseases such as type 1 diabetes, rheumatoid arthritis, Crohn’s disease and colitis. All are more common in people who get very little sun exposure, as are maladies such as Alzheimer’s and cardiovascular disease that appear to have some immune system and inflammatory connections.

Scientists not involved in the light research are more cautious, but they agree that something important is going on

could also solve a mystery that has vexed scientists for more than a century: Why do people living in lower-light environments have such high rates of disease?

In 1974 pioneering researcher Margaret L. Kripke (who would go on to found the department of immunology at MD Anderson Cancer Center in Texas) discovered that she could induce tumors in the skin of mice by exposing the rodents to UV light

why was the tumor able to grow in the original irradiated mouse? Was the UV light that had induced it also somehow suppressing the mouse’s natural immune response? In a series of experiments, Kripke determined that UV radiation was indeed a double whammy. Not only did it damage DNA in skin cells and trigger mutations that could lead to cancer, but it also suppressed the immune system’s surveillance of the skin, preventing that system from killing any budding cancers.

The discovery of UV light’s powerful impact on our immune responses launched a brand-new discipline: photoimmunology. Early investigators in this field, such as Kripke, focused on the negative effects of immunosuppression. But they soon found some upsides as well. For example, it finally explained something doctors had noticed for centuries: sunlight soothed psoriasis, a skin condition marked by painful, itchy scales.

For more than a century scientists have noticed that many diseases, especially autoimmune and cardiovascular conditions, follow a latitude gradient. Once other confounding factors such as diet, exercise and socioeconomics are accounted for, rates of these diseases rise with latitude. All kinds of causes have been suggested—climate, diet, cosmic rays, something in the water—but nothing fit.

in 1980

noticed a strong north-south gradient for colon cancer rates and suggested in a hugely influential paper in the International Journal of Epidemiology that vitamin D was responsible.

everywhere scientists looked they discovered an inverse correlation between vitamin D levels and the risk of dozens of diseases, including breast cancer, high blood pressure, diabetes, heart attack, stroke, dementia, depression, and several autoimmune disorders.
Thus began the vitamin D era.

But as recently chronicled in this magazine, rigorous clinical trials have shown that extra D supplementation—using the vitamin as a treatment—doesn’t help with any of these diseases.

The disease with the most dramatic latitude gradient is MS.

The gradient exists worldwide and has been growing stronger over time. It even shows up within individual countries, including France, the U.K., Sweden, New Zealand, Canada and the U.S.

Some of the best data comes from Australia, which is one of the only countries to boast a wide range of latitudes, a relatively homogeneous population and a national health-care system with good recordkeeping

But in 2010 Lucas read a study showing that UV treatments protected mice against MS without affecting their vitamin D levels

kids who spent less than 30 minutes a day outside had twice the risk of MS compared with those who spent up to one hour outside and about five times the risk of those who averaged more than an hour outside.

observational studies like these cannot prove causation. There could be other explanations for the patterns. Perhaps people suffering the earliest symptoms of MS spend more time indoors because they’re not feeling well.

within the same region, MS relapse rates follow a seasonal cycle—higher in winter, when sun is scarce—and incidence rates correspond closely to birth month, being highest in people who experienced winter during their first trimester of gestation, when the brain and immune system are developing

The fact that the effect lasted for months after the initial UV treatment was intriguing.

the UV hadn’t just suppressed the immune cells in circulation; it had reset the system to a more tolerant state

“You get this rebalancing,” Hart says. “UV light calms inflammation in the skin. But it also then calms inflammation in the central nervous system. It’ll calm inflammation in the pancreas and the gut. So I think it’s not fully realized the potential it has to be a controller of body homeostasis.”

In recent years researchers have learned that many other chronic conditions also have an inflammatory component. Cardiovascular disease is caused in part by immune cells attacking and damaging the walls of blood vessels. Alzheimer’s disease is connected to low-grade, smoldering inflammation in the brain. Arthritis, asthma, allergies, diabetes and even depression are thought to have inflammatory components.

Although some scientists have argued for increased sun exposure for people at high risk of an autoimmune disease, few health-care providers would ever be comfortable recommending a known carcinogen to their patients

a pill would be better than a light box as a treatment, MacMahon says. “People prefer pills,” he says, and doctors prefer prescribing pills, and pharmaceutical companies definitely prefer making pills.

when you do shine UV light on the skin and take a peek to see what it makes, you discover a microscopic pharmacopeia. In addition to vitamin D, the skin produces melatonin, serotonin, endorphins, endocannabinoids, cortisol, oxytocin, leptin, nitric oxide, cis-urocanic acid, itaconate, lumisterol, tachysterol, and a dozen other vitamin D–like compounds that don’t even have names yet.

Likewise, phototherapy itself is unlikely to deliver all the benefits of full-spectrum sunlight, but it doesn’t have to. Its safety, simplicity and affordability mean all it has to do is deliver some benefit. “Phototherapy is so cheap relative to biologics,” Hart says. “It’s almost a no-brainer as an adjunct treatment for all these inflammatory autoimmune diseases.”

A UV light box costs about $2,000, whereas adalimumab (Humira), a leading biologic drug for various autoimmune diseases, lists for $80,000 a year and must be taken for life.

Kaiser Permanente provided 2,200 of its psoriasis patients with free at-home UV light boxes as an experiment. Fewer than a third of them went on to use biologics. Kaiser Permanente now lists at-home UV as a recommended treatment for psoriasis.

But Langer-Gould, the MS expert at Kaiser Permanente, says that although she’d be interested to see whether the light boxes the insurer uses for psoriasis would be helpful for MS, it’s too soon to make that leap. “Hart’s data are very encouraging,” she says. “But the current evidence is not enough to conclude a definitive treatment effect and recommend widespread use. We need at least one more study.”

In the meantime, the flexibility of phototherapy will allow Young and other converts to fashion their own healing protocols—independence that becomes all the more precious when you have a debilitating disease.