Benefits of Sunlight: A Bright Spot for Human Health 10

As science continues to study sunlight, the old sun-protection paradigm keeps failing.  Learn how past studies on sunlight exposure, Vitamin D, and UV light are now considered unreliable.  Part 10 is the final section of M. Nathaniel Mead’s in-depth look at sunlight research on the human body: Benefits of Sunlight: A Bright Spot for Human Health.

Benefits of Sunlight: A Bright Spot for Human Health

M. Nathaniel Mead
Research Challenges

Growing evidence of the beneficial effects of UVR exposure has challenged the sun-protection paradigm that has prevailed for decades. Before a sun-exposure policy change occurs, however, we need to know if there is enough evidence to infer a protective effect of sun exposure against various diseases.

Only through well-designed randomized clinical trials can cause-and-effect relationships be established. However, most sunlight-related epidemiologic research to date has relied on observational data that are subject to considerable bias and confounding. Findings from observational studies are far less rigorous and reliable than those of interventional studies. But interventional studies would need to be very large and carried out over several decades (since most UVR-mediated diseases occur later in life). Moreover, it is not at all clear when, over a lifetime, sun exposure/vitamin D is most important. So for now scientists must rely on the results of well-conducted observational analytic studies.

In sunlight-related research, there are two main exposures of interest: vitamin D status, which is measured by the serum 25(OH)D level; and personal UVR dose, which involves three fundamental factors: ambient UVR (a function of latitude, altitude, atmospheric ozone levels, pollution, and time of year), amount of skin exposed (a function of behavioral, cultural, and clothing practices), and skin pigmentation (with dark skin receiving a smaller effective dose to underlying structures than light skin).

When measuring sun exposure at the individual level, many scientists have relied on latitude or ambient UVR of residence. But these measures are fraught with uncertainties. “While ambient UVR varies, . . . so too do a variety of other possible etiological factors, including diet, exposure to infectious agents, temperature, and possibly even physical activity levels,” says Robyn Lucas, an epidemiologist at Australia’s National Centre for Epidemiology and Population Health. “Additionally, under any level of ambient UVR, the personal UV dose may vary greatly. In short, there is no real specificity for ambient UVR.”

Researchers also assess history of time in the sun at various ages, history of sunburns, dietary and supplemental vitamin D intake, and other proxy measures. Nonetheless, says Lucas, “there are drawbacks to inferring that a relationship with any proxy for the exposure of interest is a relationship with personal UV dose or vitamin D status.” On the bright side, she adds, our ability to accurately gauge an individual’s UV dose history has been enhanced with the use of silicone rubber casts of the back of subjects’ hands. The fine lines recorded by the cast provide an objective measure of cumulative sun damage.

Source: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2290997 , http://www.scribd.com/doc/6480898/Benefits-of-Sunlight-A-Bright-Spot-for-Human-Health

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Tags: Research, science, UV, UVR, vitamin d