Rethinking Vitamin D and Sun Exposure Guidelines

Sun protection
Sun protection
From scientific studies to niche-market magazines, supplements are in the spotlight.

From scientific studies to niche-market magazines, supplements are in the spotlight. A recent article published in Outside magazine, a publication for outdoor recreation enthusiasts, questioned the complicated relationship of sun exposure, sunscreen use, and vitamin D.1

Lower mortality rates from cardiovascular disease (CVD) and cancer have been observed in populations residing in regions with greater exposure to sunlight, a requisite for cutaneous vitamin D synthesis.2 Similarly, low serum levels of 25-hydroxyvitamin D have been linked with increased risks for CVD and cancer.2 Because of the risk for skin cancer associated with sun exposure, vitamin D supplementation has frequently been recommended as a strategy to reduce cancer and CVD risk.

However, because of the dearth of conclusive findings on this topic, both the US Preventive Services Task Force and the Institute of Medicine have stated that evidence regarding the effectiveness of vitamin D supplementation to reduce cancer and CVD risk is insufficient.3,4 Numerous study limitations have been cited, including insufficient statistical power, inadequate sample size and trial duration, and the use of low doses of vitamin D.2

The Latest on Vitamin D

In the Vitamin D and Omega-3 Trial (VITAL; NCT01169259) published January 2019 in the New England Journal of Medicine, researchers from Brigham and Women’s Hospital and Harvard Medical School in Boston, Massachusetts, sought to address these gaps.2 They conducted a randomized, placebo-controlled trial involving 25,871 American adults who were healthy at baseline (51% women; mean age 67.1 years).

The sample included 5106 black participants, for whom the issue of vitamin D is “particularly relevant because their cutaneous synthesis of vitamin D in response to solar radiation is lower than that in persons in other racial or ethnic groups,” according to the researchers. Participants were randomly assigned to one of the following conditions: vitamin D, n-3 fatty acids, both agents, or both placebos. The median follow-up period was 5.3 years (range, 3.8-6.1 years).

The results showed no significant differences among groups in the incidence of cancer or CV events. The authors noted that their trial examined only one dose of vitamin D, and ongoing studies are investigating the effects of various doses. Additionally, a “2-year post-intervention follow-up of our cohort is ongoing to capture latency effects and increase statistical power to assess end points,” the authors wrote.

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Reconsidering Sun Exposure

Other recent findings appear to support the positive health effects of sunlight itself, with the implication that perhaps current sun exposure guidelines may be too rigid or even harmful. Multiple studies have reported beneficial effects of sun exposure on CV and metabolic parameters, including blood pressure, by means of increased plasma levels of nitric oxide metabolites.5 Research published in 2018, however, failed to demonstrate a reduction in blood pressure in 10 healthy participants after ultraviolet-A exposure that was roughly equivalent to 30 minutes of summer sun.5

Study authors did observe associated increases in plasma (nitric oxide 2−), as well as reductions in whole body oxygen utilization and resting metabolic rate, which “suggests that exposure to sunlight has a meaningful acute impact on metabolic function.”

This article originally appeared on Medical Bag