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 makes vitamin D. Vitamin D is also available as a dietary supplement.
Vitamin D serves many purposes in your body, including:
— Helping build bones and absorb calcium, which is also crucial for healthy bones.
— Reducing inflammation.
— Supporting a healthy immune system. Vitamin D 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.
— Lowering cancer risk. 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: D2 is from plant-based sources, and D3 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 Recommended Dietary Allowance or 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. In fact, a 2019 study in the American Journal of Clinical Nutrition noted that, based on data from the National Health and Nutrition Examination Survey 2011-2014, a project overseen by the Centers for Disease Control and Prevention, 18.3% of participants had a serum (blood) level of vitamin D that was categorized as being at risk of inadequacy.
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 as of 2018, 42% of the U.S. population is deficient in vitamin D.
Certain populations are at greater risk of being deficient, with Black people and people over the age of 65 having higher rates of vitamin D deficiencies. People with darker skin have more melanin, the pigment that gives the skin its color, which reduces their ability to produce vitamin D when exposed to sunlight. Older adults also have trouble making enough vitamin D, and this is especially true for those with mobility issues who may be confined mostly indoors.
On average, U.S. adults are thought to get 160 to 400 IU per day of vitamin D from dietary sources, 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:
— Diet shortfalls. If your diet doesn’t include enough foods that are high in vitamin D, that could lead to a deficiency.
— Lack of outdoor activity. 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.
— Sunblock. Many people use sunscreen to protect their skin from harmful UV rays, which can limit the skin’s ability to make vitamin D.
— Geographic location. If you live farther away from the equator, you probably have less exposure to the type of sunlight that promotes vitamin D production in the skin, says Michelle Bauche, a clinical dietitian with the Weight Management and Metabolic Institute at University of Missouri Health Care in Columbia.
— Genetics. 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 dietary 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 can 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.
— People with a body mass index of 30 or greater. 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.
— Breastfed infants. 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:
— Musculoskeletal pain.
— Fatigue and listlessness, or an overall sense of feeling tired, not feeling like being productive and wanting to lie down all day.
— More frequent infections and illnesses.
— Mood changes.
— Muscle aches or pains.
— A softening of the bones that presents as rickets in children and as osteomalacia in adults, Bauche says. Rickets is very rare, but can present in children as incorrect growth patterns, weakness, pain in muscles and bones and deformities in joints, Hardie says. Osteomalacia may not show many symptoms early on, but can lead to fractures, particularly in weight-bearing bones.
— Osteoporosis. Chronic vitamin D deficiency can put you at a higher risk for fractures and osteoporosis, Webster says.
Of course, these same signs could be associated with many other nutritional deficiencies and health problems, such as stress, dehydration or achy joints caused by weather changes, Hardie says. If you have these signs and suspect they’re 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 30 to 50 ng/dL (nanograms per deciliter).
What to Do If You’re 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. A 3-ounce serving of sockeye salmon provides 71% of the RDA for vitamin D. A 3.5-ounce serving of fresh Atlantic herring provides 216 IU of vitamin D, or 27% of the RDA. A 3.5-ounce serving of canned tuna is another good source, offering 268 IU or 34% of your RDA of vitamin D.
— Fortified dairy products and non-dairy milks. These products 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. While mushrooms are a potential vitamin D source, the amount of vitamin D they have increases if they’ve been exposed to UV light in the growing process. For instance, a half-cup of portabello 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. Similarly, dried mushrooms are higher in vitamin D than fresh.
— Other fortified foods. Orange juice and cereals are commonly fortified with vitamin D and can help you meet your needs. 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. The amount of time in the sun you’ll need depends on where you live — it’s not going to be practical for most people to spend 10 or 15 minutes outdoors in the dead of a Maine winter to get some vitamin D — and how dark your skin is. People with lighter skin need less time in sunlight to manufacture vitamin D, while those with darker skin need longer.
And, you still need to be careful of not overdoing sun exposure without sun protection, as skin cancer is always a potential issue if you’re spending time outdoors without using sunblock or covering your skin. For this reason, the American Academy of Dermatology 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 per day is considered 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 who are profoundly deficient may receive vitamin D supplement prescriptions of up to 50,000 IU weekly for brief periods of time, usually 12 weeks. You can use either D2 or D3 supplements, although D3 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 as part of a comprehensive bone health regimen.
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Update 05/14/21: This article was previously published and has been updated.