What does the evidence show?
New research explores how ultraviolet light can trigger the production of health- and performance-boosting nitric oxide
The only vitamin pill I take these days is vitamin D. Over the years, I’ve reluctantly come to the conclusion that an isolated micronutrient is generally a poor substitute for the richly complex food it was extracted from, so I try to stick to the original sources for my vitamin needs. Of course, living in Canada makes it hard to do that with vitamin D for much of the year, so I’ve clung to the hope that sunshine can, in fact, be bottled.
Perhaps predictably, an interesting new study just published in the European Journal of Applied Physiology from a group led by Chris Easton of the University of the West of Scotland, hints that there’s more to the picture. Apparently, exposure to sunlight can also affect levels of nitric oxide in your body, which may have interesting implications for both health and sports performance.
The study involved shining two different doses of ultraviolet light (specifically UVA light—wavelengths between 315 and 400 nanometers) on ten volunteers, then measuring its effects on a range of outcomes like blood pressure, resting metabolism, and nitrite and nitrate levels. It’s this last bit that caught my attention, because the rise of beet juice as an endurance-boosting supplement is due to its high levels of nitrate. The body converts that nitrate to nitrite and then to nitric oxide, which seems to make your muscles work more efficiently during endurance exercise. These studies have also found that boosting levels of nitric oxide has other health benefits, like acutely lowering blood pressure and regulating blood sugar. (In fact, one recent study found that using mouthwash twice a day or more, which wipes out the oral bacteria that convert nitrate to nitrite, was associated with a 50 percent increase in the risk of developing prediabetes or diabetes.)
It turns out previous studies have shown that the skin contains a lot of nitrite, and when it’s exposed to sunlight, this nitrite is released into the blood and ultimately (like beet juice) leads to an increase in nitric oxide levels. So this study aimed to see how much UVA light is necessary to produce this effect.
The two doses they used were ten and 20 joules per square centimeter, with the higher dose chosen to be equivalent to “approximately 30 min of Mediterranean summer sunlight.” The results were a bit of a mixed bag. Both doses of light successfully lowered resting metabolic rate, which was assessed by measuring oxygen consumption (VO2), but only the higher dose significantly increased nitrite levels. Neither dose affected blood pressure, in contrast with previous findings. A bunch of methodological details may explain these discrepancies, such as exactly how the light was delivered and when the outcomes were measured.
Still, the overall data, according to the authors, suggests that “exposure to sunlight has a meaningful acute impact on metabolic function.” And that’s intriguing, because there are all sorts of seasonal patterns in health, like increases in heart attacks and strokes during winter months. These patterns are commonly attributed to a shortage of sunlight-induced vitamin D, but the link between ultraviolet light and nitric oxide levels may offer another explanation.
When I asked Easton, the study’s lead author, about this, he mentioned that he and his colleagues are just finishing collecting data to see if there are seasonal fluctuations in nitric oxide bioavailability in people living in Scotland, much like the seasonal fluctuations seen in vitamin D levels. Given the seasonal change in heart and other health conditions, “it is possible that a reduced availability of nitric oxide contributes to this additional risk,” Easton said, “but we don’t know for sure.” In the meantime, he figures focusing on getting more nitrate-rich leafy green vegetables than usual during winter months is a good plan.
The other question I asked Easton was whether UV light might enhance endurance performance. His answer: “Possibly.” The amount of nitric oxide you get from sunlight is small compared to what you get from food sources like beets, and it’s also highly variable, depending on factors like skin tone and prior sun exposure. But he and his colleagues did a study in 2015 that combined real (or sham) UVA exposure with real (or placebo) nitrate gel before a ten-mile cycling time trial. In the particular conditions they tested, neither the UVA light nor the nitrate gels on their own boosted performance by a statistically significant margin—but the combination of UVA light and nitrate gels did, suggesting that the additional nitric oxide contributed by the light exposure had a measurable effect.
Please, please, please do not interpret this as a suggestion that you should rush out and get a tanning bed. For now, there are more questions than answers in this research, and we’re a long way from thinking about practical applications. And if you think this study confirms that Alberto Salazar was onto something when he shipped a Whole-Body Light Pod to Brazil for his athletes to use before the 2016 Olympics, think again: That gadget delivers red and near-infrared light rather than ultraviolet light. To me, the takeaway is much simpler—a reminder that getting outside is good for you in ways that we’re just starting to unravel. Accept no substitute.
My new book, Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, with a foreword by Malcolm Gladwell, is now available! For more, join me on Twitter and Facebook, and sign up for the Sweat Science email newsletter.