Why Your Body Needs Vitamin D Vitamin D helps the body absorb calcium, which is vital for forming and maintaining strong bones and teeth. Research has also shown that vitamin D acts similarly to a hormone in the body and may play a role in regulating blood pressure, weight and mood. One recent study even suggests that having adequate levels can protect against early fatalities from conditions like cancer and heart disease.
When adults don't get enough vitamin D, they can suffer from osteomalacia (a softening of the bones), osteoporosis, bone pain or muscle weakness.
Vitamin D is also a key component in brain development, and a deficiency may contribute to low energy or depressive symptoms, says Jim White, RD, owner of Jim White Fitness and Nutrition Studios in Virginia Beach.
1. Sunlight is the best source. The body can make its own vitamin D, but only when skin is exposed to sunlight. For most people, spending just five to 30 minutes outside twice a week is enough for the body to synthesize healthy levels of vitamin D. The sun needs to shine on bare skin on your face, arms or legs, without sunscreen. (Keep in mind, exposing your skin to UVA and UVB rays for any amount of time can increase your chances of skin damage and melanoma.)
But those people who don't spend time outdoors, live far from the equator, have dark skin or use sunscreen every time they go out may not be able to produce the same quantity of vitamin D. Many people also have lower levels in cold-weather months, when most of us are spending less time outdoors.
2. Fortified foods can help, too. Although most of our vitamin D comes from the sun, we can also get a substantial amount from food. Fatty fish (including herring, mackerel, sardines and tuna) and eggs contain vitamin D naturally, and many juices, dairy products and cereals are fortified with the vitamin, as well.
It's probably not possible to get the full, recommended amount of vitamin D -- 600 IU for adults up to age 70 -- from dietary sources alone, says Smith. "It's not found naturally in many foods, and even those that do have it don't contain nearly enough to meet the body's needs," he explains. "Vitamin D must come from multiple sources including diet, sunlight and sometimes supplements."
3. Vitamin D may improve athletic performance. A recent review published in the American College of Sports Medicine's Health & Fitness Journal concluded that people who are deficient in vitamin D may have compromised fitness levels. Studies have found, for example, that athletes could jump higher or sprint faster after they took supplements for several weeks or months.
But more is not always better, the review cautions: If you already have healthy levels of vitamin D, taking a supplement probably won't have an impact on your strength, speed or athleticism.
4. There's a good chance your levels are low. Extreme vitamin D deficiency -- defined as less than 12 nanograms of vitamin D per milliliter of blood -- is rare in the United States, but people who follow a strict vegan diet or have dairy allergies are at risk since they are not eating foods (like fish, eggs and milk) with naturally occurring or added vitamin D. Age and weight also play a factor in deficiency, says White. "As we get older and our kidneys become weaker, they may not be able to convert enough vitamin D into the active form that our bodies can use." Obesity can also lead to a deficiency, he adds, as the nutrient is leached out of the blood by body fat.
While most of us aren't dangerously low on vitamin D, we don't all have ideal levels, either. Current guidelines recommend that adults have at least 20 nanograms of vitamin D per milliliter of blood, says White, although 30 is an even better number for optimal bone and muscle health. Most Americans get close to meeting this guideline, but about two-thirds of us fall slightly short -- especially in the winter when we're not outside regularly.
5. A supplement may improve your health ... or it may not. A 2013 study from the University of Auckland in New Zealand found that many adults who took vitamin D pills to help prevent osteoporosis didn't actually reap significant bone-building benefits. Still, White suggests that people who are vegan, live in northern areas, have dark skin, are over 50 or who are overweight should consider taking a supplement, since they are more likely to be deficient.
If you suspect you might be low on D, talk to your doctor. He or she may want to give you a blood test to check your levels -- although a recent government initiativerecommended against routine vitamin D screenings, since there's no consensus in the medical community on how helpful they really are. "I recommend that healthy adults get screened less frequently than those adults who are not as healthy," says Smith.
The bottom line: Whether you take a supplement should be a decision you make with your doctor, based on your individual risk factors and any symptoms you may be experiencing.