With our lifestyles, oftentimes the sun can seem like a myth. If you run early in the morning or in the evening—spending all day in an office in between—it’s easy to miss even the slightest hint of natural light. That can make you feel sluggish, chronically sick and slightly depressed. It can even make you run slower.
A growing body of research has found a number of negative health effects resulting from a lack of sunlight, and a lack of corresponding Vitamin D. These range from poor bone density to weak immune systems to links to diabetes and cardiovascular disease. There is increasing research, as well, that suggests Vitamin D deficiencies can impact athletic performance.
“We know that Vitamin D is important for optimal skeletal and muscle function,” says D. Enette Larson-Meyer, an associate professor at the University of Wyoming, who has studied Vitamin D extensively and wrote a review of its athletic importance for the Gatorade Sports Science Institute.
One study found improved sprint times in soccer players. Another suggested that muscles get stronger with increased Vitamin D intake. There’s even some suggestion that sunnier months (and places) correlate with improved oxygen uptake.
In fact, in the 1950s the Eastern bloc countries were so convinced of the link between Vitamin D and athletic performance that they stuck their athletes in front of sunlamps. Those runners improved their 100m times by 7.4 percent, compared to a 1.7 percent improvement for non-sunned runners. There was even a temporary dispute over whether loading up on Vitamin D amounted to cheating, explains John Cannell, a doctor who was so convinced of the benefits of Vitamin D that he founded the Vitamin D Council. (He also wrote the book on the subject, Athlete’s Edge: Faster, Quicker, Stronger with Vitamin D.)
To a degree, some of the reasons Vitamin D might make you faster, quicker and stronger are relatively straight-forward. The vitamin, which isn’t even really a vitamin, primarily comes from direct sunlight absorbed through the skin. (There are also a few minor food sources, such as fatty fish and fortified dairy products, like milk.) It then helps you absorb calcium. Calcium is necessary for healthy bones. So, without enough Vitamin D, your bones are more likely to fracture. This is not good for runners who want to stay uninjured. “It’s especially important for athletes,” says Emily Brown, a former professional runner and a wellness dietician for the Mayo Clinic. One study of NFL players found that those with Vitamin D deficiencies were more likely not just to have fractures, but to be cut from the team.
Vitamin D also keeps your immune system functioning well. That means that Vitamin D-deficient athletes, who often already have weakened immune systems because of training loads, tend be sick more frequently. Sick athletes are not happy athletes. Improving your bone health and your immune health “will translate into more high-quality training days,” says Larson-Meyer.
The other more complicated and less well-understood benefit has to do with muscle function. The vitamin actually operates as a hormone. It regulates processes within your muscular system and keeps inflammation down. People who have Vitamin D deficiencies tend to complain about general muscle soreness. And one study of ballet dancers found that muscle strength and vertical jump improved after a four-month Vitamin D supplement regime.
But a lot about how Vitamin D works and how much is good isn’t fully understood yet. “Maybe it’s Vitamin D. Maybe it’s Vitamin D and something else,” says Larson-Meyer. “But the evidence is pretty strong that Vitamin D does something to optimize performance.”
The one thing we do know is that you probably aren’t getting enough.
Vitamin D deficiencies are rampant in the U.S., says Cannell, since we are a society that mostly works indoors and, as more has been understood about skin cancers, one that also generally slathers on the sunscreen. That’s not a bad thing, but it may be too much of a good thing. What has surprised researchers is that even runners, who spend a decent amount of time outside, have been found to be very low in Vitamin D.
That doesn’t mean we should start doing all our runs with no clothes and no sunscreen. “You don’t want to think of your training time as also your time to get Vitamin D,” says Brown.
All you really need is about 10 minutes of direct high sun on your full body a few times per week—just your face and hands won’t be enough. The rule of thumb, explains Larson-Meyer, is that you need half the time it takes before you start to turn pink, about three times per week. That varies depending on how far north you live and your genes, but for most of us that means just 10-20 minutes at a time.
In the winter, though, even 10 minutes outside without a coat or hat sounds cold and miserable. “Those are times you maybe want to focus on dietary sources,” says Brown, and possibly take a supplement. It’s not 100 percent clear yet if supplements have the same full effect as natural Vitamin D from the sun, according to Cannell. “We don’t know for sure,” she says. But it’s better than nothing.
The only problem is that Vitamin D is a fat-soluble vitamin. That means both that you need some fat in your diet in order to process the mineral, and that it is possible to overdose and hit a toxic level. Most people aren’t anywhere near that level, but that’s why Larson-Meyers advises anyone concerned about their Vitamin D level to get a blood test to see where they’re at before they start taking supplements.
The federal government recommends your level be at 20 nanograms per milileter, but Cannell says 40-50 ng/ml is optimal. If you’re low, you can take supplements, but recommendations on those vary as well. Larson-Meyers suggests taking 1,500-2,000 IU/day; Cannell recommends up to 5,000 IU/day. Natural levels, Cannell argues, come from when we were a more outdoors society.
“Do you want to be like a computer programmer, or a hunter-gather?” he asks.