Vitamin D

Vitamin D (calciferol) is a fat-soluble vitamin. Your skin makes it when ultraviolet B (UVB) rays from the sun strike it. It is also found in a few foods and in supplements, says the NIH (the US National Institutes of Health).

The vitamin itself is inactive. The liver and then the kidney turn it into calcitriol, a hormone that helps the gut absorb calcium and phosphate and keeps bone mineralized.

It comes as vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), and 1 mcg (microgram) equals 40 IU (international units).

Here is the part most people do not know: your skin cannot always make it. In a classic experiment, human skin in winter sunlight in Boston (42°N) made no previtamin D3 from November through February. In Edmonton (52°N) it made none from October through March. Skin from people aged 77 and 82 made less than half as much as skin from 8- and 18-year-olds.

The second surprise is in the trials. Low vitamin D in the blood goes along with many diseases. Yet large trials of daily vitamin D in adults not chosen for deficiency, like VITAL (25,871 people), found no fewer cancers, heart events or fractures. The best-supported jobs are the basic ones: preventing rickets and osteomalacia (soft bones in children and adults) and keeping bones mineralized.

Health benefits of vitamin D

• ★★★No clear drop in fractures or fallsIn 81 trials in adults, vitamin D supplements did not clearly cut fractures (1.00 times as likely) or falls (0.97 times). In a Cochrane review, vitamin D plus calcium lowered hip fractures slightly (0.84 times as likely).
• ★★★No fewer heart attacks or strokesIn 21 trials of vitamin D supplements, major cardiovascular events were 1.00 times as likely as without them. Heart attack was 1.00 times as likely and stroke 1.06 times, so supplements did not lower them.
• ★★★Fewer cancer deaths, but not fewer deaths overallIn 52 trials of vitamin D supplements, death from any cause was not clearly different (0.98 times the risk). Cancer deaths were lower (0.84 times the risk; the authors give 16%).
• ★★Slightly fewer respiratory infectionsPooled trials found a small drop in the odds of a respiratory infection (0.88 times). In a larger update, 61.3% of people on vitamin D had one, against 62.3% on placebo.
• ★★High-dose pills raised high blood calcium riskIn 22 trials of 3,200 to 4,000 IU a day, high blood calcium was 2.21 times as likely (about 4 extra cases per 1,000 people). Falls were also more likely (1.25 times).

Foods high in vitamin D

Few foods contain much vitamin D, and fatty fish lead. In our USDA-based ranking, one mackerel fillet (112 g) has 18 mcg, 90% of the 20 mcg Daily Value (the FDA label value). Farmed Atlantic salmon follows at 9.4 mcg in 3 oz (85 g), then sardines at 4.4 mcg per can (92 g). Herring has 3.6 mcg in 3 oz and one large egg 1 mcg.

Per 100 g, mackerel has 16.1 mcg and salmon 11 mcg. Only 11 foods in our database carry a vitamin D value. So the ranking leaves out some foods that matter in many diets, such as fortified milk, UV-treated mushrooms and cod liver oil.

The NIH table fills the gap. Cod liver oil has 34.0 mcg per tablespoon, and farmed rainbow trout 16.2 mcg and sockeye salmon 14.2 mcg per 3 oz cooked. White mushrooms exposed to UV light give 9.2 mcg per ½ cup and fortified 2% milk 2.9 mcg per cup. Fortified soy, almond and oat milks give 2.5 to 3.6 mcg per cup, and fortified cereal about 2.0 mcg per serving.

Fortified foods provide most of the vitamin D in American diets, the NIH says. In 2015 to 2016 the average adult got only 4.2 to 5.1 mcg a day from food and drink. Mushrooms make vitamin D2, and animal foods vitamin D3.

Animal foods also hold some 25(OH)D, which is about five times as potent as the parent vitamin per microgram, according to the NIH. FoodData Central (the USDA food database) does not list it, so the ranking above understates these foods.

Cooking costs little in fish. Rainbow trout kept 85% to 114% of its vitamin D3 across boiling, steaming, microwaving, pan-frying and baking, with pan-frying lowest at 85%. UV-treated mushrooms kept 62% to 88% of their vitamin D2.

How vitamin D works

The biochemistry below is well established. But it comes from skin experiments, physiology studies and reviews rather than from trials of extra vitamin D in people.

Four ideas cover most of it. Sunlight starts the process in the skin, and age and skin color change how much the skin makes. The liver and kidneys turn the vitamin into a hormone, and that hormone helps the gut take up calcium. Then comes what has been seen in people.

Sunlight starts it in the skin

UVB radiation of about 290 to 320 nanometers turns 7-dehydrocholesterol in the skin into previtamin D3, the NIH says. That then becomes vitamin D3. UVB does not pass through glass, so sitting in a sunny window does not work. Season, time of day, cloud, smog, skin pigment and sunscreen all change how much arrives.

In a classic experiment, human skin exposed to sunlight on cloudless days made no previtamin D3 in Boston from November through February. In Edmonton it made none from October through March, while at 34°N and 18°N sunlight still worked in midwinter.

The sun does not cause vitamin D toxicity, the NIH says. The skin turns the excess previtamin D3 into forms that are not vitamin D. But the NIH also says UV radiation is a carcinogen (a cause of cancer) and advises sun protection.

Age and skin color change how much the skin makes

The skin pigment melanin absorbs UVB, and the raw material in the skin falls with age. In skin samples from people aged 8 to 92, the epidermis (outer skin) held less 7-dehydrocholesterol with age. Skin from people aged 77 and 82 made more than two times less previtamin D3 than skin from people aged 8 and 18.

Young healthy volunteers got the same whole-body UVB dose. Blood vitamin D3 rose to 31.4 nmol/L in white volunteers, 27.8 in East Asian, 12.8 in South Asian and 9.1 in black volunteers. The study’s terms were white, Oriental, Indian and black. Even so, levels of the active hormone were similar in all groups.

The NIH adds that it is not clear whether the lower 25(OH)D of people with dark skin has significant health consequences. African Americans have lower rates of fracture and osteoporosis than white Americans.

The liver and kidneys turn it into a hormone

Vitamin D from the skin, food or supplements is inactive and needs two hydroxylations (chemical steps), says the NIH. The liver makes 25-hydroxyvitamin D [25(OH)D], also called calcidiol, which has a half-life of about 15 days. It is the form a blood test measures. The kidney mainly makes 1,25-dihydroxyvitamin D [1,25(OH)2D], or calcitriol, the active hormone.

Its half-life is only hours. Parathyroid hormone, calcium and phosphate keep it tightly controlled, which is why it does not fall until deficiency is severe.

EFSA (the EU’s food safety agency) puts the average absorption of vitamin D from a usual diet at about 80%. It says 25(OH)D is stored in fat, muscle and liver. The NIH adds that neither aging nor obesity changes absorption in the gut. But body fat holds on to more of the vitamin, so people with obesity may need more.

The hormone helps the gut take up calcium

Calcitriol binds to the vitamin D receptor inside cells. In the gut it helps absorb calcium and phosphorus, and in the kidney it helps the body reclaim calcium. In bone it works with parathyroid hormone, according to EFSA. Without enough, calcium absorption falls and bone mineralizes poorly, which causes rickets in children and osteomalacia in adults.

One human experiment measured calcium absorption at two vitamin D levels. It was 65% higher when 25(OH)D averaged 86.5 nmol/L than when it averaged 50.2 nmol/L. Both values lie inside the usual reference range, though.

What has been seen in people

The clearest human findings are about deficiency and bone. Rickets and osteomalacia come from too little vitamin D or calcium, and fortification and supplements made rickets rare in the US. In people who already have enough, extra vitamin D has done little. Large trials and meta-analyses found no effect on fractures, falls, cancer cases, heart disease, depression or death from all causes.

Daily doses lowered respiratory infections only slightly, and large yearly or monthly doses were linked to more falls. The Endocrine Society’s 2024 guideline suggests vitamin D for children and teens aged 1 to 18, adults 75 and older, pregnancy and high-risk prediabetes. It suggests against going above the recommended intake in healthy adults under 75. The trials behind these statements are among the study cards above.

How much vitamin D do you need?

Adults need 15 mcg (600 IU) of vitamin D a day up to age 70, according to the US recommended dietary allowance (RDA). After that age they need 20 mcg (800 IU), and infants need 10 mcg (400 IU); one mcg equals 40 IU. EFSA’s adequate intake in the EU is 15 mcg (600 IU) for adults and for children aged 1 to 17. For infants aged 7 to 11 months it is 10 mcg.

Both sets of values assume little or no sun. The NIH says the US allowances assume minimal sun exposure. EFSA says that when the skin makes vitamin D, the dietary need is lower or may even be zero.

On labels, the FDA Daily Value is 20 mcg (800 IU) and the EU Reference Intake is 5 mcg. Those are label yardsticks, not personal targets.

Pregnancy and breastfeeding keep the US allowance at 15 mcg (600 IU), and EFSA sets the same 15 mcg as for other adults. For older adults, the US allowance rises to 20 mcg (800 IU) after age 70, while EFSA keeps 15 mcg for all adults.

Other bodies differ. The NIH notes that the UK’s Scientific Advisory Committee on Nutrition recommends 10 mcg (400 IU) from age 4. The American Academy of Pediatrics advises a 10 mcg (400 IU) supplement a day for breastfed infants from shortly after birth. The reason is that human milk alone provides less than 0.6 to 2.0 mcg per liter.

Some people need more to reach the same blood level. The NIH says people with obesity may need more, because body fat holds on to the vitamin.

A post hoc analysis (done after the fact) looked at a 12-month trial in 221 older adults in Lebanon. Their mean body mass index was 30.2, and all took 1,000 mg of calcium.

A daily 600 IU gave a mean 25(OH)D of 26.0 ng/mL, and 86% reached 20 ng/mL (50 nmol/L). On 3,750 IU, the figures were 36.0 ng/mL and 99%. The authors conclude that 600 IU a day does not bring 97.5% of ambulatory older adults above that threshold.

Sun, skin type, latitude and age all change what you need. Some expert bodies suggest about 5 to 30 minutes of sun without sunscreen, mostly between 10 a.m. and 4 p.m. It should reach the face, arms, hands and legs. Daily or at least twice a week, that usually gives enough, they say, but the NIH says too many factors vary to set a rule.

Winter light at high latitudes can make none, and older and darker skin makes less. Daily SPF 50+ sunscreen lowered levels by 5.2 nmol/L in a year-long trial. The NIH still advises sun protection, because UV radiation is the most preventable cause of skin cancer.

The other way to judge intake is a blood level, and bodies define it differently.

The US National Academies (NASEM) say a 25(OH)D below 30 nmol/L (12 ng/mL) raises the risk of deficiency. From 30 to under 50 nmol/L (12 to under 20 ng/mL) is inadequate for some people. At 50 nmol/L (20 ng/mL) or more it is sufficient for most. Above 125 nmol/L (50 ng/mL) it may bring harm.

EFSA chose 50 nmol/L as its target for setting the adequate intake. The Endocrine Society’s 2024 guideline found no clear evidence for an optimal target, and suggests against routine testing in healthy people. Some trials use higher cut-offs: CORONAVIT counted below 75 nmol/L as suboptimal.

One nmol/L equals 0.4 ng/mL. The NIH warns that different lab assays can give a falsely high or low result for the same sample.

Vitamin D deficiency: signs and who is at risk

Deficiency shows up as rickets in children and osteomalacia in teenagers and adults, the NIH says. In rickets the bones fail to mineralize, which causes soft bones and deformities. Severe cases can bring failure to thrive, developmental delay, seizures from low blood calcium and dental problems. Osteomalacia has similar signs: bone pain and deformities, seizures, muscle spasms and dental problems.

The NIH says rickets became rare in the US after milk fortification began in the 1930s. But it is increasing again around the world, including in the US and Europe, especially among immigrants from African, Middle Eastern and Asian countries.

The NIH lists the people most at risk. They include breastfed infants who get no supplement, older adults, and people with dark skin. People with limited sun exposure are on the list too: homebound people, people who cover their skin and people with indoor jobs. So are people with conditions that limit fat absorption, such as some liver disease, cystic fibrosis, celiac disease, Crohn’s disease and ulcerative colitis.

People with obesity or gastric bypass surgery are also at risk, as are people who eat little dairy or follow an ovo-vegetarian or vegan diet. In US survey data, deficiency below 25 nmol/L was more than twice as common in people who used oral steroids (11% against 5%).

In 2011 to 2014, 5% of Americans aged 1 and older were at risk of deficiency (below 30 nmol/L). The share at risk of inadequacy was 18%. Across 55,844 Europeans, 13.0% had levels below 30 nmol/L and 40.4% below 50 nmol/L.

A blood test for 25(OH)D is the main way to check status. The US Preventive Services Task Force (an expert panel) found insufficient evidence to weigh the benefits and harms of screening adults without symptoms. The Endocrine Society’s 2024 guideline suggests against routine testing in the general population, including people with obesity or dark skin.

Neither applies that advice to people with an established reason to test, such as bone disease or poor fat absorption. So ask a doctor if you have one.

Forms of vitamin D: absorption and effects

Vitamin D supplements come as D2 (ergocalciferol) or D3 (cholecalciferol). D2 is made by irradiating ergosterol from yeast. D3 is typically made by irradiating 7-dehydrocholesterol from sheep’s wool, and the NIH says an animal-free D3 from lichen is also sold. Calcifediol (25-hydroxyvitamin D3) is one step further along in the body.

Products also differ in dose schedule, in whether they are taken with a meal, and in format, such as capsules, gummies and sprays.

The honest bottom line: nearly all of these comparisons measure the blood level of 25(OH)D, not health outcomes. D3 raised the level more than D2 in most comparisons, but the gap disappeared with daily dosing in one meta-analysis. The NIH says both forms seem equally able to cure rickets.

Calcifediol is several times as potent per microgram, but the NIH says no calcifediol supplements appear to be available to US consumers. For gummies, sprays and lichen D3 the evidence is thin.

The outcome trials in the benefits section used vitamin D3 capsules or tablets. They were VITAL, D2d, D-Health, RECORD, DO-HEALTH, Burt and the Women’s Health Initiative, where it came with calcium carbonate.

Form	Activity or conversion	What studies show	Source
Vitamin D3 (cholecalciferol)	1 mcg = 40 IU	Raised 25(OH)D more than D2 in a meta-analysis of randomized trials, mainly with bolus doses, and by 15.3 to 16.9 nmol/L more in a 12-week trial of 15 mcg a day in juice or biscuits. The NIH says it also holds the higher levels longer. Used in the large outcome trials.	1, 2, 3
Vitamin D2 (ergocalciferol)	1 mcg = 40 IU	Raises 25(OH)D and, per the NIH, seems as good as D3 at curing rickets. In the meta-analysis the gap to D3 was lost with daily dosing. D2 from UV-treated mushrooms raised levels like a D2 supplement in 26 people.	1, 2, 3, 8
Vegan D3 from lichen	Not stated	The NIH says an animal-free D3 from lichen is available. We found no trial comparing it with other D3.	1
Calcifediol (25-hydroxyvitamin D3)	NIH: 3 to 5 times as potent per mcg as D3	Each microgram raised 25(OH)D about 5 times as much as D3 in a 10-week winter trial in 56 older adults. A review of nine trials found it 3.2-fold more potent. The NIH says it is not sold to US consumers as a supplement.	1, 4, 5
Gummies	Not stated	One crossover study found higher blood vitamin D3 from gummies than from tablets after a single 20,000 IU dose. It did not report 25(OH)D or outcomes.	9
Buccal spray	Not stated	A review of four trials found it not clearly better than other delivery methods.	10
Fortified cheese	Not stated	In 80 adults given weekly servings, vitamin D3 in fortified cheeses raised 25(OH)D about as much as the same dose in a liquid supplement.	13

Here are the head-to-head and form-specific studies, strongest evidence first, 8 in all.

Taking it with a meal is a popular tip. Fat in a meal raised the peak of blood vitamin D3 by 32% after a single 50,000 IU dose in 50 older adults. The NIH says fat in the gut enhances absorption, although some vitamin D is absorbed without it.

In 17 patients who were not responding to treatment, moving the dose to the largest meal raised 25(OH)D by 56.7% on average. But that study had no control group. The randomized meal trial above found no difference in 25(OH)D after 90 days. In 80 adults, a liquid supplement taken with food and without food raised levels by the same 59.3 nmol/L.

Daily, weekly or monthly is the other common question. Daily dosing raised levels most in nursing home residents. In the meta-analyses of infections and cancer deaths, the daily-dose subgroups looked better than large bolus doses.

The Endocrine Society’s 2024 guideline suggests daily rather than intermittent high doses for people over 50 who need vitamin D. Large intermittent doses (500,000 IU once a year, 60,000 IU a month) were linked to more falls in two trials.

Is vitamin D safe? Supplements, dose and interactions

Vitamin D from food and from the sun is not a safety concern, the NIH says: toxicity is almost always caused by supplements.

The US tolerable upper intake level (UL, the daily maximum) is 100 mcg (4,000 IU) from age 9 on, including pregnancy and breastfeeding. It is 25 mcg (1,000 IU) for ages 0 to 6 months and 38 mcg (1,500 IU) for 7 to 12 months. It is 63 mcg (2,500 IU) for ages 1 to 3 and 75 mcg (3,000 IU) for ages 4 to 8.

EFSA’s upper level is 100 mcg for adults, including pregnant and breastfeeding women, and for ages 11 to 17. It is 50 mcg for ages 1 to 10. For infants, EFSA’s 2018 update keeps 25 mcg up to 6 months and sets 35 mcg for 6 to 12 months.

EFSA based the adult level on a no-effect dose of 250 mcg a day in two studies in men. The NASEM committee said signs of toxicity are unlikely below 250 mcg (10,000 IU). It noted, though, that even intakes under the upper level might have adverse effects over time. In 2013 to 2014, 3.2% of US adults took supplements with 100 mcg or more.

• Toxicity. Too much vitamin D causes high blood calcium, the NIH says. That can bring nausea, vomiting, weakness, confusion, thirst and kidney stones. In extreme cases it brings kidney failure, calcium deposits in soft tissues, abnormal heart rhythm and death. Toxicity has followed manufacturing errors. Seven children were admitted with a median blood calcium of 16.5 mg/dL. A fish oil supplement had held about 4,000 times the labeled vitamin D3. They recovered with treatment and had no kidney calcification at one year. The NIH adds that frequent tanning-bed use can push levels well above 375 to 500 nmol/L.
• Doses in trials. In a meta-analysis of 22 trials of 3,200 to 4,000 IU a day, high blood calcium was about twice as likely (relative risk 2.21). That meant 4 extra cases per 1,000 people, and falls and hospital stays were also higher. Over 3 years, 4,000 and 10,000 IU a day lowered bone density compared with 400 IU. One yearly dose of 500,000 IU raised falls and fractures. Possible high urinary calcium was more common at 28,000 IU a week in pregnancy.
• Kidney stones. In the Women’s Health Initiative, 1,000 mg of calcium with 400 IU of vitamin D3 a day raised kidney stones by 17%. That was over 7 years. The NIH says other, shorter trials of vitamin D alone or with calcium found more high blood and urinary calcium but not more kidney stones.
• Drug interactions. The NIH lists several. Orlistat can lower vitamin D absorption. Statins may reduce vitamin D synthesis, while very high vitamin D might blunt atorvastatin, lovastatin and simvastatin. Corticosteroids such as prednisone reduce calcium absorption and impair vitamin D metabolism. Thiazide diuretics lower urinary calcium, and with vitamin D they can cause high blood calcium. That is especially so in older adults and people with kidney problems or an overactive parathyroid.
• Who should ask a doctor. People with kidney disease or hyperparathyroidism (an overactive parathyroid) should check first. So should people taking thiazide diuretics, orlistat, statins or steroids, and anyone planning to take more than the upper level. The Endocrine Society’s 2024 guideline suggests against taking more than the recommended intake to lower disease risk in healthy adults under 75.

How to get more vitamin D

• Best foods. One mackerel fillet gives 18 mcg and 3 oz of farmed Atlantic salmon 9.4 mcg in our ranking. The NIH adds cod liver oil at 34.0 mcg per tablespoon and UV-treated mushrooms at 9.2 mcg per ½ cup. Fortified milk gives 2.9 mcg per cup. Cooking costs little: trout kept 85% to 114% of its vitamin D3.
• Sun, with care. Some expert bodies suggest about 5 to 30 minutes of sun a few times a week on bare skin is usually enough. But a year of daily SPF 50+ sunscreen lowered 25(OH)D by 5.2 nmol/L, and the NIH still advises sun protection.
• Daily supplement, if needed. Daily doses are the best-studied schedule, and D3 raised levels more than D2 in several comparisons. A meal with fat raised absorption in one trial, though blood levels after weeks did not differ in another. Stay under 100 mcg (4,000 IU) a day unless a doctor directs otherwise.

History of vitamin D

Rickets was described long before vitamin D was known. The English physicians Daniel Whistler (1645) and Francis Glisson (1650) gave the first clear descriptions. Cases rose from the 17th to the 19th century as people crowded into smoggy industrial cities. Doctors blamed syphilis, tuberculosis, bad air and bad diet, and the real cause stayed unclear until the 1920s.

In 1917 the pediatrician Alfred Hess pioneered cod liver oil supplements in an African American community. In 1919 Mellanby wrote that rickets is a deficiency disease caused by the lack of an anti-rachitic food factor. McCollum, who had suspected a fat-soluble factor, named it vitamin D. Animal experiments by Shipley and Park showed that cod liver oil and UVB light both healed rickets.

Fortified food, cod liver oil and infant formula cut rickets over the following decades, and the NIH dates milk fortification from the 1930s. Rickets came back in waves, first among immigrants to Europe in the 1960s and 1970s. It is back again now in Australia, Canada and New Zealand, partly because of sun avoidance and sunscreen. In 2016 an international group of experts published global guidance on preventing and treating nutritional rickets.

Frequently asked questions about vitamin D

How much vitamin D should you take a day?

Adults need 15 mcg (600 IU) a day up to age 70 and 20 mcg (800 IU) after that in the US. EFSA’s adequate intake for adults is 15 mcg. These values assume little sun, so people who get regular sun may need less. The US upper limit is 100 mcg (4,000 IU) a day. The Endocrine Society’s 2024 guideline suggests supplements for children and teens aged 1 to 18, adults 75 and older, pregnancy and high-risk prediabetes. It suggests against going above the recommended intake in healthy adults under 75.

Can you get enough vitamin D from food alone?

Rarely, unless you eat fatty fish often or use fortified foods. In 2013 to 2016 US survey data, 94% of people aged 1 and older got under 10 mcg (400 IU) from food and drink. In 2015 to 2016, adult men averaged 5.1 mcg and women 4.2 mcg. One mackerel fillet gives 18 mcg and a large egg 1 mcg in our ranking. Sunlight supplies part of the rest, and the NIH says most Americans still have adequate blood levels.

Which is better, vitamin D2 or D3?

D3 raised blood 25(OH)D more in a meta-analysis of randomized trials. It also did in a 12-week trial of 15 mcg a day, where it gained 15.3 to 16.9 nmol/L more than D2. But the gap was lost with daily dosing in the meta-analysis, and the NIH says both forms seem equally able to cure rickets. These comparisons measured blood levels, not health outcomes. In a meta-analysis of mortality trials, D3 trials showed lower all-cause mortality than D2 trials, but neither form alone made a clear difference.

Does vitamin D need to be taken with food?

Not necessarily, but fat in a meal can help absorption. Fat raised the peak of blood vitamin D3 by 32% after one 50,000 IU dose in 50 older adults. Yet in a 90-day trial, 25(OH)D levels did not differ between meal types. In 80 adults, a liquid supplement taken with or without food raised levels by the same 59.3 nmol/L. In these studies the difference in blood levels after weeks was small or absent.

Does vitamin D prevent colds or COVID-19?

Slightly for colds and other respiratory infections, and mostly in people who start very low. A pooled analysis of 25 trials found 0.88 times the odds, and 0.30 times in daily or weekly users who started below 25 nmol/L. A 2021 update of 46 trials found 0.92 times. The 6,200-person CORONAVIT trial found no fewer infections or COVID-19 cases with 800 or 3,200 IU a day.

Do vitamin D supplements prevent fractures and falls?

Not on their own. A meta-analysis of 81 trials found no effect on fractures (1.00 times the risk) or falls (0.97 times). A Cochrane review found that vitamin D with calcium lowered hip fracture risk slightly (0.84 times), while vitamin D alone did not. A yearly dose of 500,000 IU and monthly doses of 60,000 IU were linked to more falls.

Does sunscreen stop you making vitamin D?

It lowers it a little. In a year-long trial of 628 Australians, people used SPF 50+ sunscreen on days with a UV index of 3 or higher. That lowered 25(OH)D by 5.2 nmol/L. The comparison was using sunscreen at will, and 45.7% against 36.9% had levels below 50 nmol/L. The NIH notes that people rarely apply enough sunscreen to cover all skin, and it still advises sun protection to prevent skin cancer.

Should I get my vitamin D level tested?

Usually not, if you are healthy and have no risk factors. The Endocrine Society’s 2024 guideline suggests against routine testing in the general population. The US Preventive Services Task Force found insufficient evidence on screening adults, and the NIH notes that lab assays vary. A test makes sense for people with bone disease, poor fat absorption or another established reason, on a doctor’s advice.