Vitamin D is an important vitamin that you get through some of the foods you eat and through sun exposure. When skin is exposed to the sun, it can make vitamin D. Vitamin D is alsoavailable as a dietary supplement.
Vitamin D serves many purposes in your body:
— Helps build bones and absorb calcium, which is also crucial for healthy bones.
— Reduces inflammation.
— Can help prevent muscle cramps and spasms.
— Supports a healthy immune system. It can decrease your risk of getting a viral infection like the flu and lower an infection’s severity if you do get sick, says registered dietitian Sonya Angelone, a San Francisco area-based spokesperson for the Academy of Nutrition and Dietetics.
— Some health experts believe that vitamin D may lower your risk for certain types of cancer, such as colorectal cancer. Research in this area is ongoing.
There are two types of vitamin D important to humans: D 2 is from plant-based sources, and D 3 is made by the body when the skin is not protected by sunscreen and is exposed to ultraviolet rays in sunlight.
The recommended daily allowance for vitamin D for children and adults is 600 IU (15 mcg) until age 70. Starting at age 70, the RDA is 800 IU (20 mcg). In infants up to a year old, the RDA is 400 IU. All of these RDAs assume that a person gets minimal sun exposure, but federal guidelines don’t specify how much sun exposure that means.
Vitamin D Deficiency Is Common
Many Americans are believed to be vitamin D deficient. A report from the Centers for Disease Control and Prevention states that 8.1% of Americans are deficient in vitamin D, although other studies and estimates cite a much higher percentage. For example, Cleveland Clinic Mercy Hospital, a ministry of the Sisters of Charity Health System, based in Ohio, estimates that 42% of the U.S. population is deficient in vitamin D. In the CDC study, the highest deficiency was found among Black people, with 31% found to be vitamin D deficient.
On average, U.S. adults are thought to get 160 to 400 IU per day of vitamin D, which increases to 300 to 900 IU daily when supplements are used, according to the Dietary References for Calcium and Vitamin D from the National Academies of Science, Engineering and Medicine.
There are a few reasons why people may not get enough vitamin D:
— It’s not often found in food sources.
— Although you can get vitamin D from the sun, many of us don’t get a lot of outdoor exposure because of work that confines us indoors. In addition, many people use sunscreen to protect their skin from harmful UV rays. Plus, if you live farther away from the equator, you probably have less exposure to sunlight, says Michelle Bauche, a clinical dietitian with the Weight Management and Metabolic Institute at University of Missouri Health Care in Columbia.
— Some people have gene variants that make it hard for their bodies to produce vitamin D, even if their skin is exposed to ultraviolet light.
There’s also a wide swath of the population that commonly has vitamin D deficiency. These subgroups include:
— Older Americans. It’s harder to absorb vitamin D as you age. This is one reason why higher vitamin D amounts are recommended for adults age 70 or older.
— Those who have indoor jobs because they aren’t outside in the sun a lot, says Antonette Hardie, a registered dietitian at the Ohio State University Wexner Medical Center in Columbus.
— Those who have darker skin.
— Those with inflammatory bowel disease or cystic fibrosis because these diseases make it harder for the body to absorb vitamin D.
— Those who are vegan or lactose tolerant and certain types of vegetarians could struggle to get enough vitamin D, Hardie says. That’s because the food sources that provide vitamin D are often from animals, such as dairy and fish.
— Those who are obese. Body fat can isolate vitamin D instead of spreading it to other parts of the body, says registered dietitian Ali Webster, director of research and nutrition communications at International Food Information Council in Washington, D.C. Obesity is considered a body mass index of 30 kg/m2 or higher.
— Breastfed infants. That’s because breast milk is not a good source of vitamin D, and infants shouldn’t be exposed directly to the sun, Webster says. Breastfed infants should receive a 400 IU vitamin D supplement a day until they can consume 1,000 milliliters of vitamin D-fortified formula or whole cow’s milk daily, according to the American Academy of Pediatrics.
Signs of Vitamin D Deficiency
There are several signs of vitamin D deficiency, including:
— Bone and joint pain.
— More frequent infections and illnesses.
— Mood changes.
— Muscle aches or cramps.
— A softening of the bones that presents as rickets in children and as osteomalacia in adults, Bauche says.
— Chronic vitamin D deficiency can put you at a higher risk for fractures and osteoporosis, Webster says.
— An overall sense of feeling tired, not feeling like being productive and wanting to lay down all day.
— Rickets, which is very rare, is caused by a severe lack of vitamin D and shows up in children as incorrect growth patterns, weakness, pain in muscles and bones and deformities in joints, Hardie says.
Of course, these same signs could be associated with many other health problems, such as stress, dehydration or achy joints caused by weather changes, Hardie says. If you have these signs and suspect that they are linked to vitamin D deficiency, talk to your health provider about getting a blood test that can check for vitamin D deficiency.
A normal level from a vitamin D lab test is usually considered to be 20 to 40 ng/mL, but some health providers like to see levels closer to 30 to 50 ng/mL.
What to Do If You Are Vitamin D Deficient
If a lab test indicates that you’re not getting enough vitamin D, there are a few things you can do.
First, turn to food. Some good food sources for vitamin D include:
— Fatty fish such as salmon. A 3-ounce serving of sockeye salmon provides 71% of the RDA for vitamin D.
— Dairy products and non-dairy milks, all of which are usually fortified with vitamin D. A cup of 2% cow’s milk provides 15% of the vitamin D children and adults need daily. For non-dairy milks, a cup will provide 13% to 18% of an adult’s RDA for vitamin D.
— Eggs. One egg has 6% of the RDA for vitamin D.
— Liver. Three ounces of liver provides 5% of the RDA for vitamin D.
— Mushrooms are a potential vitamin D source, but the amount of vitamin D they have increases if they have been exposed to UV light in the growing process. For instance, a half-cup of portabella mushrooms has just 1% of the RDA of vitamin D, but when exposed to UV light, that spikes to 120%, according to the Mushroom Council. Look on the packaging for a note that indicates the mushrooms have been treated with UV light.
— Orange juice and cereals that are fortified with vitamin D. One regular-sized serving of cereal usually provides 10% of the daily value needed of vitamin D.
Eating a well-rounded, overall healthy diet can help you to obtain more vitamin D, Hardie says.
Next, aim to get just a few minutes of sunlight a day. After all, vitamin D is often called the sunshine vitamin. However, this sun exposure sans sun protection requires just a small amount of time — 10 to 15 minutes a day should be enough, with some of your skin (like your arms or legs) exposed.
The American Academy of Dermatology, however, advises people to get their vitamin D from food sources, not the sun.
A third option in place of or in addition to food and sun exposure is a dietary supplement. This is best done in collaboration with your health provider, who can help decide on the right dosing for you. In general, 1,000 to 5,000 IU is considered to be safe, Bauche says. These higher doses are used because many people won’t absorb all of the vitamin D that their body gets, Angelone says. Some people receive vitamin D supplement prescriptions of up to 50,000 IU weekly. You can use either D 2 or D 3 supplements, although D 3 supplements are more common.
A few tips to help choose a good vitamin D supplement:
— Find out if a supplement will interact with any medicines you’re using. For instance, the cholesterol-lowering drug cholestyramine can cut down your absorption of vitamin D.
— Look for a supplement with a USP seal. This indicates the product has been verified for its purity, strength and manufacturing quality by the U.S. Pharmacopoeia. This is a key step because dietary supplements aren’t regulated by the Food and Drug Administration, Webster warns.
— Purchase directly from the manufacturer. Supplements offered by third-party distributors may not be stored in ideal conditions or could be counterfeit, Bauche cautions.
— Ask your health provider if you should use other supplements along with vitamin D, Angelone advises. Some health experts will want you to use vitamin K2 or magnesium along with vitamin D to help your body better absorb vitamin D.
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Update 04/05/21: This article was previously published and has been updated with new information.