Vitamin D is well-known for being important for bone health. It’s also been studied for its possible link to a lower risk of a wide variety of conditions. But even though you can get vitamin D from food, supplements, or spending time in the sunshine, many people don’t get enough of it.
Why? Maybe you don’t get enough of it from your diet. Other things that affect your body’s ability to make vitamin D include the season, time of day, where you live, air pollution, cloud cover, sunscreen, body parts exposed, skin color, and age. Dermatologists recommend using sunscreen and getting vitamin D from food and supplements rather than risk the harmful rays of the sun.
Role of Vitamin D
Vitamin D is naturally present in few foods. But it’s in many fortified foods.
Since 1930, virtually all cow's milk in the U.S. has been fortified with 100 IU of vitamin D per cup. Food makers fortify other foods such as yogurt, cereal, and orange juice.
"Vitamin D deficiency is associated with low bone mass and osteoporosis, which is estimated to affect 10 million adults over the age of 50 in the U.S.," says Atlanta rheumatologist Eduardo Baetti, MD. He says many of his patients – especially elderly and dark-skinned people – have low levels of vitamin D because the sun is not a reliable source.
How Much Vitamin D Do You Need?
The National Institutes of Health recommends that people get this much vitamin D daily:
- Birth to 12 months: 10 micrograms (mcg) or 400 international units (IU)
- Ages 1-70 years: 15 mcg (600 IU)
- Ages 71 and older: 20 mcg (800 IU)
Older adults need more vitamin D because as they age, their skin does not produce vitamin D efficiently, they spend less time outdoors, and they tend to not get enough vitamin D.
Best Sources of Vitamin D
The sun is an excellent source of vitamin D, but it is hard to quantify how much vitamin D you get from time in the sun, and the risk of skin cancer may outweigh the benefits.
Food first, says Baylor College of Medicine dietitian Keli Hawthorne. "Supplements can fill in the gaps, but it is always better to try to meet your nutritional needs with foods that contain fiber, phytonutrients, and so much more," she says.
Unless you enjoy a diet that includes fatty fish or fish liver oils, it may be hard to get enough vitamin D naturally without eating fortified foods or taking a supplement. "The major dietary source of vitamin D comes from fortified dairy, along with some yogurts and cereals," Hawthorne says. Mushrooms, eggs, cheese, and beef liver contain small amounts.
How Much Is Too Much?
Because vitamin D is a fat-soluble vitamin, it can build up in the body. So it is possible to get too much of it.
The National Institutes of Health says these are the upper limits per day for vitamin D:
- Birth to 6 months: 25 mcg (1,000 IU)
- Babies 7-12 months: 38 mcg (1,500 IU)
- Children 1-3 years: 63 mcg (2,500 IU)
- Children 4-8 years: 75 mcg (3,000 IU)
- Children 9-18 years: 100 mcg (4,000 IU)
- Adults 19 and older: 100 mcg (4,000 IU)
- If pregnant or breastfeeding: 100 mcg (4,000 IU)
"There is a potential to cause harm if you overdose on supplements above 4,000 IU/day, but there is no fear of overdosing from the sun, because your skin acts like a regulatory system, only allowing production of the amount of vitamin D you need," says Patsy Brannon, PhD, a Cornell University professor of nutritional sciences who served on an Institute of Medicine committee that reviewed vitamin D recommendations.
Acceptable Vitamin D Blood Levels
Part of the confusion about whether or not you are getting enough vitamin D may be the definition of the acceptable blood level of vitamin D, clinically measured as 25-hydroxyvitamin D [25(OH)D].
Using vitamin D blood levels is the best estimate of adequacy that accounts for dietary intake and sunshine, yet experts differ on what that level should be.
"A 25(OH)D blood level of at least 20 nanograms/ml was used by the IOM committee to set the recommendations for vitamin D because this level showed adequacy for a wide variety of bone health indicators" says Brannon.
The Endocrine Society Practice Guidelines, as well as many laboratories and experts, recommend a minimum vitamin D blood level of 30 nanograms/ml as an acceptable level.