Get full access to Outside Learn, our online education hub featuring in-depth fitness and nutrition courses and more than 2,000 instructional videos when you sign up for Outside+.
You may know it as calcium’s trusty sidekick, but there’s much more to vitamin D than keeping your bones healthy and strong. Like you, this small but mighty vitamin is gaining a reputation as a fierce multitasker with recent studies linking it to everything from reduced cancer risk to improved mental health and even a longer life. “Vitamin D is the key — the only key — to several thousand genes that help regulate nearly everything in your body,” says John Cannell, MD, executive director of the Vitamin D Council, a nonprofit organization that aims to increase vitamin D awareness.
But that’s not all. During the past couple of years, researchers have increasingly been linking this “superstar” vitamin to some impressive fitness benefits in healthy women. Researchers from McGill University discovered that when healthy female college students had low levels of vitamin D, they accumulated more fat in their muscles — a factor that impacts not only how fit you look but also how strong you are, according to the researchers.
And that’s already on top of past studies that have drawn a connection between vitamin D levels and improved athletic performance, reduced belly fat and improved muscle-building. If that’s not enough reason to consider making vitamin D your wingman in health and fitness, we don’t know what is.
Here, our experts present you with a plan of attack.
Are You Getting Enough?
The toughest part of getting on top of your vitamin D habit is figuring out how much you need in the first place. In 2011, an expert committee of the Institute of Medicine of the National Academies (a national organization that serves as an adviser on how to improve health in the United States) set new vitamin D guidelines, raising them from 400 international units (IUs) per day to 600 IUs per day for adults under the age of 70 — that’s three times the previously recommended amount.
But ask any doctor or nutritionist how much you need and the recommendations often range up to 2,000 IUs or more per day. “The bottom line is that there is controversy,” explains Dee Sandquist, MS, RD, LD, a spokesperson for the American Dietetic Association (ADA).
While the word is still out on whether how much you weigh impacts how much vitamin D you need, the science shows that women with a higher body fat usually need more vitamin D than lean women to achieve the same blood levels, says Carol Wagner, MD, a neonatologist, vitamin D researcher and professor of Pediatrics at Medical University of South Carolina.
“That’s because vitamin D is fat soluble, so extra body fat holds on to the vitamin D and does not allow it to get into the blood stream as well as in lean women,” she says. Still, some experts, such as Kari Gans, MS, RD, CDN, a New York City nutritionist, suggest that active women get a range of between 1,000 to 2,000 IU of vitamin D daily to boost health and athletic performance. “The right amount of vitamin D may make you faster, stronger and improve your balance and timing,” she says.
The Real Deal on Supplements
So how can you get all that vitamin D? One way is by spending extra time outdoors. Get about 20 to 30 minutes without sunscreen when the sun is high in the sky (UVB doesn’t break through the atmosphere when the sun is low on the horizon), says Cannell, as your skin uses energy from the sun’s rays to produce vitamin D in your body. But here’s the catch: People with dark skin need up to six times that amount of time (that’s up to three hours!), and heading outdoors without wearing sunscreen for any period of time may raise your risk of sun damage and skin cancer.
Plus, as Harvard researchers report, if you live south of the line between San Francisco, California, and Richmond, New York (what scientists call the 37th parallel), your skin can only make enough vitamin D during the summer — and even then production may be affected by clouds or other factors.
The next approach may be through your diet, but vitamin D is naturally present in very few foods, and in small amounts. If you’re shooting for up to 2,000 IU per day, you’ll have to chew on more than 13 ounces of salmon, or (gulp!) 80 eggs every day to meet your needs.
So what’s an active gal to do? Speaking with your doctor about taking a vitamin D supplement is a good place to start. You will find that supplements are available in two types: Either D2, an egrocalciferol format (made from plants or yeast), or D3, which is cholecalciferol, made from animal products such as sheep’s wool. Most experts recommend D3 because it has been shown to metabolize better in the body and be more effective in raising blood levels of vitamin D. As for choosing a liquid (drops) or solid (tablets) format, “all forms are absorbed by your GI tract, so choose the form that suits you best,” says Wagner. Since many multivitamins contain about 400 IU, you may need to take D3 on its own in addition to the multivitamin.
A study in the Journal of Bone and Mineral Research also found that taking vitamin D supplements with the largest meal of the day doubled the subjects’ blood levels. Translation? If you’re eating the most calories in the mornings, take your supplement at the same time as breakfast. In addition, make sure that your meal includes a source of healthy fat, which will help the vitamin D properly absorb in your body.
While the safety margin on vitamin D supplements is wide, “Intake greater than 10,000 IU per day has not been proven safe for extended periods of time unless directed by your doctor,” says Wagner, so don’t assume that more is better and let your physician know how much you’re taking.
Taking The Test
Once you’ve formed a healthy vitamin D habit, maintaining it is important. Just as you get your oil changed every three months and your teeth cleaned every six months, checking your vitamin D levels on a regular basis can help you cruise to a better, healthier body. Gans suggests asking your doctor to have your levels checked every year during your physical, or if you feel that your levels are low starting out. A simple blood test, called the 25-hydroxyvitamin D, or 25[OH]D test, measures the circulating form of vitamin D in your body.
Some insurance companies will pay for the test; if not, it costs about $50. It might sound pricey, but it can help you to know where you stand and help you and your doctor determine the best plan of action so that your vitamin D levels stay strong — and your muscles and body too.