UNC Health Care
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Everything You Need to Know About Vitamin D

If you want strong bones and teeth, vitamin D is a big help. And while it isn’t naturally found in many food sources, you can boost your vitamin D levels simply by going outside in the sun.

According to the most recent figures from the Centers for Disease Control and Prevention, about 8 percent of Americans have a vitamin D deficiency. Many more have inadequate vitamin D levels in their bodies.

Mallory McClester Brown, MD, a UNC Health primary care physician, and Lana Nasrallah, a UNC Health clinical dietitian, explain everything you need to know about the vitamin.

The Benefits of Vitamin D

Vitamin D boosts calcium and phosphorus absorption into bones and teeth, making them more resilient. This helps prevent bone loss and the development of skeletal disorders such as osteoporosis. Vitamin D also:

  • Helps regulate how much calcium is in your bloodstream, which helps with heart function, among other roles
  • Supports the immune system by fighting off harmful bacteria and viruses
  • Corrects mineral imbalances to keep your kidneys healthy
  • Improves muscle function
  • Keeps nerves and nerve receptors healthy to encourage good brain-body communication
  • Reduces inflammation

Given all these benefits, a lack of vitamin D in the body can cause problems, including:

  • Osteoporosis or other bone issues that can result in weak bones and a high risk of fracture
  • Weak muscles that can increase the risk of falls in older adults

How to Get Vitamin D

The most natural way to get vitamin D is with sunlight.

“The body uses ultraviolet (UV) rays from sunlight that shines on the skin to make, absorb and use vitamin D,” Nasrallah says. “The amount of vitamin D the body makes from sun exposure depends on many factors, including the time of day, season of the year, geographic latitude, skin tone and lifestyle.”

Brief exposure to the sun without sunscreen—10 to 30 minutes maximum, two to three times a week—is the most efficient way to spur the production of vitamin D in the body. Each person’s ideal exposure time will be different; lighter-skinned people will need less time (and are more likely to burn), while darker-skinned people typically require more time in the sun.

Dr. McClester Brown is adamant that the vast majority of the time that people are exposed to the sun, they should be wearing sunscreen.

“UVB rays are the specific wavelength that trigger vitamin D production in the skin, but they are also potentially damaging and can cause skin cancer,” Dr. McClester Brown says.

Speaking of ultraviolet light: Doctors never recommend artificial tanning, even for a brief period, as a way to increase vitamin D. The risk of skin cancer is too high, Dr. McClester Brown says.

When it comes to your diet, fatty fish such as salmon, tuna, mackerel and sardines are some of the only foods that naturally provide a good source of vitamin D. Items including milk, yogurt, orange juice, alternative milk products and breakfast cereals are sometimes fortified with vitamin D; check their labels.

“In addition, beef liver, cheese and egg yolks provide natural sources of vitamin D in small amounts,” Nasrallah says. “Mushrooms also contain this vitamin if grown under ultraviolet lights.”

How Much Vitamin D Is Enough?

Some people have trouble getting enough vitamin D in their diets because their bodies don’t create it or process it properly. Vitamin D is a fat-soluble vitamin, meaning it needs fat to break it down for absorption into your system. People with inflammatory bowel diseases (Crohn’s disease, ulcerative colitis), celiac disease or cystic fibrosis have trouble absorbing fat and may not get enough vitamin D.

If your diet is restricted because of an allergy or because you’re on an eating plan that limits certain food groups, you might be at risk of not getting enough vitamin D from food.

“People should consult their doctor before they change eating plans to make sure they are still getting a full and healthy diet,” Nasrallah says. “And if you think you may not be getting enough vitamin D in your diet, also talk to your doctor before you start taking a supplement.”

Your doctor can tell you your levels with a simple blood test. It’s important to know before you add a supplement, because there is such a thing as too much vitamin D, Dr. McClester Brown says. “If you take too much, you can increase your risk of kidney stones, and if you take too much for too long, it could potentially cause cardiac complications,” she says.

So what is the right amount? The National Institutes of Health says the recommended daily amount of vitamin D is 400 international units (IU) for children up to 12 months, 600 IU for ages 1 to 70, and 800 IU for people older than 70. For reference, a cup of 2 percent milk fortified with vitamin D contains 120 IU, and 3 ounces of sockeye salmon contains 570 IU.

Vitamin D, Age and Race

Vitamin D is very important at the beginning and in the later years of life. For babies and children, it helps grow strong muscles and bones. For older adults, it helps reduce bone and muscle loss. But people in these age ranges may have more trouble getting enough vitamin D.

“Breastfed infants are at risk of not consuming enough vitamin D, as breast milk is not a good source of the vitamin,” Nasrallah says. “The American Academy of Pediatrics recommends that exclusively and partially breastfed infants receive supplements of 400 IU per day of vitamin D shortly after birth.”

Infants should continue to take these supplements until they are weaned and consume at least 1,000 milliliters per day of vitamin D-fortified formula or whole milk.

Older adults are at an increased risk of developing vitamin D insufficiency as well. Dr. McClester Brown says that as we age, our bodies don’t produce as much vitamin D when we are exposed to the sun. Older adults also may experience lifestyle changes that can keep them indoors more. Postmenopausal women are particularly encouraged to take a vitamin D supplement to help prevent osteoporosis.

“While the evidence of a benefit from vitamin D supplement in men and women of other age categories is contradictory (some show a benefit, and some don’t), it’s very clear that women who have been through menopause typically see a benefit,” Dr. McClester Brown says.

Black and Latino Americans have the highest rates of vitamin D deficiency, the CDC reports. One reason for this, according to research, is that darker skin may not absorb as many UV rays, which enable the body to produce its own vitamin D. More research is needed to fully understand why these populations make up such a large percentage of vitamin D deficiencies, and whether it poses the same health problems as it does for people with lighter skin tones.


Before changing your diet or starting a vitamin D supplement, talk to your doctor. If you don’t have one, find a doctor near you.