Who Needs a Vitamin D Supplement? Food, Sunlight and Latitude

Whether a vitamin D supplement makes sense depends on what you already get from food, from sunlight and from other supplements, and on how your body handles it. This guide sets out what public health bodies say about who may need more, how sunlight, season and latitude come into it, and where blood tests fit. It is general information for healthy adults, not medical advice, and it does not diagnose anything. For what to check on the label, see our guide to choosing a vitamin D supplement.

How people get vitamin D

MedlinePlus says the body forms vitamin D after exposure to sunlight, that few foods contain much of it, and that it also comes from supplements. It describes vitamin D's job simply: it helps the body absorb calcium, a mineral that you must have for normal bone formation. The previous edition of the Dietary Guidelines for Americans (2020-2025), issued by the Department of Health and Human Services and USDA, identified vitamin D, along with calcium, potassium and dietary fiber, as a nutrient of public health concern, because many Americans do not get enough of these in their diets. The 2025-2030 edition (January 2026) is the current one; its 10-page edition does not repeat that list.

Food sources

MedlinePlus describes the main food sources this way:

• Fatty fish such as tuna, salmon and mackerel are among the richest sources.
• Beef liver, cheese and egg yolks provide small amounts.
• Mushrooms provide some, and certain mushrooms sold in stores have more because they have been exposed to ultraviolet light.
• Most milk in the United States is fortified with 400 IU per quart, which works out to roughly 100 IU (2.5 mcg) in an 8-ounce cup (the NIH Office of Dietary Supplements gives about 3 mcg, or 120 IU, per cup). Foods made from milk, such as cheese and ice cream, usually are not fortified.
• Vitamin D is added to many breakfast cereals and to some soy beverages, orange juice, yogurt and margarine, so check the nutrition facts panel.

The FDA's Daily Value for vitamin D is 20 mcg, so a cup of milk with 2.5 mcg supplies about 13% of it, the same figure the FDA's guidance works out for a 100 IU serving of milk. Our guides to reading the Nutrition Facts label and to percent Daily Value show how to find and use that number on packaged foods.

Sunlight, season and latitude

Sun is the other source, and it varies a lot. MedlinePlus says the amount of vitamin D made from sunlight can vary greatly from person to person, that people who do not live in sunny places may not make enough in a limited time in the sun, and that cloudy days, shade and dark-colored skin cut down on the amount the skin makes.

A 1988 laboratory study by Webb, Kline and Holick measured the ability of sunlight to produce previtamin D3, the first step in the skin. It found none in Boston, at about 42 degrees north, from November through February, and none in Edmonton, Canada, at 52 degrees north, from October through March. At 34 and 18 degrees north, sunlight still produced it in midwinter. The study is old and measures the sun's ability, not any person's vitamin D level, but it is the reason winter at northern latitudes comes up in advice about supplements.

Sun is not a recommended fix. MedlinePlus says exposure of more than a few minutes without sunscreen is not recommended. The American Academy of Dermatology does not recommend getting vitamin D from sun exposure or indoor tanning, says there is no safe level of UV exposure that allows maximum vitamin D synthesis without increasing skin cancer risk, and says healthy adults should get enough vitamin D from a diet that includes foods naturally rich in it.

The official intake figures already allow for this. A summary of the National Academies' 2011 report by Ross and colleagues says the vitamin D values were based on an assumption of minimal or no sun exposure, because skin synthesis varies so widely and sun carries a risk of skin cancer. The recommended amounts do not count on sunlight. Our dose and upper limits guide lists them.

Groups that may need extra

MedlinePlus says certain people may need extra vitamin D:

• Older adults.
• Breastfed infants. The American Academy of Pediatrics says breastfed infants should get 400 IU a day from a supplement, starting in the first few days of life, and recommends liquid preparations for babies.
• People with dark skin.
• People with conditions that limit the absorption of fat, such as Crohn's disease, celiac disease and ulcerative colitis.
• People who have obesity or have had gastric bypass surgery.

The AAP adds that children who take certain medications or who have chronic diseases such as cystic fibrosis may need higher doses and should ask their pediatrician. MedlinePlus advises checking with your health care provider to see whether you need a supplement and how much to take.

Do you need a blood test?

The US Preventive Services Task Force concluded in April 2021 that the current evidence is insufficient to assess the balance of benefits and harms of screening for vitamin D deficiency in asymptomatic, community-dwelling, nonpregnant adults. It issued this as an "I statement". That concerns routine screening of adults with no symptoms. Whether a test makes sense for you is a question for your clinician.

If you have had a test, MedlinePlus describes the blood level of 25-hydroxyvitamin D, written 25(OH)D, in these terms:

• Levels below 30 to 50 nmol/L (12 to 20 ng/mL) are too low for bone or overall health.
• Levels of 50 nmol/L (20 ng/mL) or above are enough for most people.
• Levels above 125 nmol/L (50 ng/mL) are probably too high.

Multiplying ng/mL by 2.5 gives nmol/L, which helps when one lab uses a different unit from another. Your clinician reads the number against your own situation.

Using this when you shop

If you and your clinician decide that a supplement fits, compare the form, the amount per serving in mcg and any outside verification, as set out in the buying guide. Searches such as vitamin D3 softgels on Amazon (opens in a new tab) show many listings, and the label on the pack, not the listing, is what counts. For a baby, the AAP says to ask your pediatrician first, and vitamin D drops for infants on Amazon (opens in a new tab) is a search for liquids made for them. Read the strength on the label of the one you buy, because liquids differ.

Questions to bring to your clinician

• Do my age, skin tone, diet, where I live or any health condition make a supplement worthwhile?
• Would a blood test help in my case?
• If I take one, how much, in mcg or IU, and in which form?
• Could it interact with any medicine I take? The FDA says to tell your provider about every supplement and medicine, especially if you are pregnant or breastfeeding.

The FDA advises talking to your doctor, pharmacist or other health care professional before you buy or use a supplement. The label is the authority on dose and warnings, and a clinician is the right person to ask about your own health.