We are all aware that too much sun exposure will lead to increased aging of the skin as well as an increased risk of skin cancer, but there are many health benefits to sunlight, and today let us look at one of them.
Researchers led by Dr. Elizabeth Arkema at the Harvard School of Public Health studied the medical records of over 200,000 women regarding sun exposure and incidence of rheumatoid arthritis (RA), and their findings were published in the February 4 Annals of the Rheumatic Diseases.
This research is one of many studies conducted as part of the massive Nurses Health Study (NHS), which followed the health of over 120,000 nurses starting in 1976, when the nurses were between 30 and 55 years old. There was also a second Nurses Health Study (NHS-II) that began in 1989. This second study followed almost the same number of nurses, but these nurses were slightly younger (age 25 to 42) than the nurses in the first study.
The health of these two large groups was carefully followed until 2008 and 2009. Researchers studied the medical records of these women to look for correlations between their health habits and how often they developed certain diseases, including RA.
Rheumatoid arthritis is a so-called “autoimmune” disease, meaning the body’s own immune system—which normally attacks bacteria and other foreign invaders—starts to attack certain parts of the body. In rheumatoid arthritis, the immune system attacks the joints, causing pain, swelling, and stiffness. RA is three to five times more common in women than men.
The Harvard researchers found that women living in states (within the U.S.) that had high amounts of UVB (ultraviolet B), had a 21% lower risk of developing RA than women who lived in states with low levels of UVB.
But interestingly, this sunlight benefit was only seen in the nurses in the first study (NHS). The nurses in the later NHS-II study did not show the sunlight benefit. The researchers felt this was because the younger nurses in the later study were likely using sunscreen more faithfully than the nurses in the first study, when there was not such a public awareness for sun protection.
The researchers conclude “Our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of rheumatoid arthritis. The mechanisms are not yet understood, but could be mediated by the cutaneous production of vitamin D and attenuated by use of sunscreen or sun avoidant behavior”.
That means the women with more sun exposure had higher levels of vitamin D in their system, and sunscreen and sun avoidance decreased the amount of vitamin D in their system. When sunlight, particularly the UV-B portion, hits the skin, the skin manufactures more vitamin D—that is why vitamin D is sometimes called the “sunshine vitamin”.
Another autoimmune disease, multiple sclerosis, has shown in studies to be less common in sunny climates. Sunlight is both good and bad for us. Too little and we are prone to vitamin D deficiencies and other problems, such as depression and perhaps certain internal cancers, but too much and our skin ages faster and we are more prone to skin cancers.
The medical research community has not decided yet what is the optimum amount of sun exposure, but it is known that just 10 to 15 minutes outside during the middle part of the day without sunscreen is adequate for our vitamin D needs. But if you are outside for longer than that, make sure you use sunscreen (and sunglasses).
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