While you may still hear secret stories about women covered in baby oil and lying on a crinkly bed of aluminum foil, sun worship has been discouraged for the last 30 years. But there's still a bright side to sunshine: Light therapy is used to treat medical conditions such as psoriasis and depression and may even prevent autoimmune disease such as multiple sclerosis (MS).

Multiple Sclerosis

Researchers have long suspected that the vitamin D in ultraviolet sunlight protects people from developing MS. This theory was first floated when scientists observed that the number of MS cases increases as the distance from the equator increases. Because ultraviolet rays (UV) from sunlight triggers vitamin D production in the skin, people at northern latitudes sometimes have a vitamin D deficiency because of the low levels of sunlight. Exposure is also affected by the time of day, weather and sunscreen usage.

"The hypothesis has been that vitamin D could reduce the risk of MS, but for a long time there was no data," says Alberto Ascherio, MD, DrPH, an associate professor of nutrition and epidemiology at the Harvard School of Public Health.

A recent study coauthored by Dr. Ascherio and published in Neurology has provided some evidence. The researchers examined the use of vitamin D supplements in 187,563 women and found that women who took a vitamin D supplement, usually as part of a multivitamin, had a 40 percent lower risk of MS than women who did not use supplements. Future studies will also examine the amount of vitamin D women receive from sunlight.

Although it's not fully understood how vitamin D might protect people from MS, Dr. Ascherio says that the vitamin may reduce the immune response against myelin, which is the protective nerve coating that is damaged by MS.

Psoriasis

While the connection between sunshine and MS is still being established, ultraviolet light has proven to be an effective treatment for the skin condition psoriasis, which can cause painful and itchy plaques.

Many people with psoriasis find that their skin improves during the summer when they're exposed to natural sunlight. Jerry Bagel, MD, director of the Psoriasis Treatment Center of Central New Jersey in New Windsor, says some people with psoriasis even choose to vacation at the beach or at the Dead Sea, which has high concentrations of minerals in the water and air that eliminate some of the sun-burning rays and maximize the ultraviolet rays' benefits.

But phototherapy administered in the doctor's office carries a smaller risk of skin cancer than sunbathing at the beach. There are two primary types of light therapy for psoriasis: ultraviolet light B (UVB) phototherapy and psoralen plus ultraviolet light A (PUVA). Children and adults treated with UVB are exposed to UBV lamps about two or three times a week for a total of about 30 treatments. With PUVA, patients are given a drug called psoralen before they are exposed to the ultraviolet light in order to make it more effective. Studies show, however, that there are a finite number of PUVA treatment fair-skinned individuals can receive before their skin cancer risk increases.

Still, both of these treatments can give psoriasis patients needed remission from their disease. So how does sunlight soothe this skin condition? In psoriasis, Dr. Bagel explains, skin cells reproduce too quickly; ultraviolet rays decrease the rate at which these overactive skin cells multiply.

Seasonal Depression

Light therapy is perhaps best known as a treatment for seasonal depression, also called seasonal affective disorder (SAD). People with SAD experience depressive symptoms such as fatigue that usually begin in the fall and improve in the early spring or summer.

While the precise cause of SAD is unknown, like MS, it's more common in the higher latitudes and is thought to be due to the availability of sunlight. It's theorized the reduced exposure to sunlight affects circadian rhythms, which is the biological clock of the body that helps regulate mood and sleep cycles. Sunlight may also have an impact on brain chemicals such as serotonin, which also affect mood.

Phototherapy for SAD is administered via light boxes or visors with white florescent light bulbs that are filtered to block ultraviolet rays. People receive their light treatment at home; it's generally recommended that people receive 30 minutes of the therapy every morning until the weather warms up.

Loving the Light

So while skin cancer is still a serious concern, these established and evolving uses of light therapy and vitamin D explains why most of us naturally crave sunlight.