About 41.9 percent of American children between 2 and 11 years old took a dietary supplement in the past 30 days. That figure comes from the National Center for Health Statistics, using national survey data collected between August 2021 and August 2023.
The American Academy of Pediatrics says healthy children eating a normal, well-balanced diet do not need vitamin supplementation beyond the recommended dietary allowances.
Both of those statements are true at the same time. The gap between them runs through every life stage covered here.
The populations where supplementation has the strongest evidence behind it are mostly not the ones being advertised to. Some of them aren’t thought of as supplement users at all.
The age curve of supplement use
The National Center for Health Statistics reported in May 2026 that 35.7 percent of Americans aged 0 to 19 and 60.2 percent of adults 20 and over had used a dietary supplement in the previous 30 days. Among adults, use climbed steadily with age: 46.3 percent at 20 to 39, 60.3 percent at 40 to 59, and 75.9 percent at 60 and older.
Inside the youth numbers the curve is a hump rather than a slope: children aged 2 to 11 were the heaviest users at 41.9 percent, teenagers aged 12 to 19 the lightest at 30.1 percent.
A 2020 CDC report in the Morbidity and Mortality Weekly Report broke that down: of everyone 19 and under in 2017 and 2018, 23.8 percent took a multivitamin-mineral product.
Now hold that against what follows. The strongest supplement recommendation in American preventive medicine applies to people who are not pregnant yet. The clearest case in the subject involves a product nobody buys, given once, in a hospital.
Before pregnancy, not during it
On August 1, 2023, the US Preventive Services Task Force issued an A grade, its highest, for folic acid. The recommendation covers anyone who is planning to become pregnant or could become pregnant, and it names a daily supplement containing 0.4 to 0.8 mg of folic acid.
The timing is the whole point. The neural tube, which becomes the brain and spinal cord, closes very early. The NIH Office of Dietary Supplements states that folic acid reduces neural tube defect risk specifically before conception and during the first 28 days after it.
Two randomized trials built the case, and they built it in two different populations. The British Medical Research Council trial, published in 1991, enrolled women who had already had a pregnancy affected by a neural tube defect, and folic acid cut the defect rate by 72 percent. A Hungarian trial reported the following year enrolled women with no such history, most of them planning a first pregnancy, and found the same direction of benefit. Article 326 carries the enrollment numbers, the outcome counts and the confidence intervals for both.
Note what the Hungarian trial also reported. Cleft lip, with or without cleft palate, was not reduced. A supplement that prevents one malformation does not prevent malformations generally.
One point the marketing obscures: the Office of Dietary Supplements states that folic acid is the only form of folate currently proven to reduce neural tube defect risk. The methylated form sold in some products has not been tested in trials for that outcome.
US bodies cluster closely on the amount. The Office of Dietary Supplements records CDC at 400 mcg a day and the American College of Obstetricians and Gynecologists at 400 mcg starting at least a month before conception. For someone with a previous affected pregnancy, several bodies list 4,000 mcg a day, ten times the general figure and under clinical supervision.
There is an upper limit, and people cross it. The tolerable upper intake level for supplemental folate is 1,000 mcg a day at ages 19 to 50, and 33.4 percent of pregnant women aged 20 to 40 exceeded it in survey data from 2001 to 2004.
During pregnancy: iodine, iron and the vitamin that works backwards
Iodine
The recommended dietary allowance for iodine in pregnancy is 220 mcg a day. The Office of Dietary Supplements reports that many professional organizations recommend a supplement before and during pregnancy, typically at 150 mcg a day. The American Thyroid Association specifies 150 mcg as potassium iodide, ideally starting three months before conception.
The agency reports that in survey data from 2017 to 2020, 63.2 percent of pregnant women fell below the urinary iodine concentration that marks sufficiency.
Iron
Here two authoritative American bodies disagree, and the disagreement is current. The American College of Obstetricians and Gynecologists recommends low-dose iron supplementation for all pregnant women starting in the first trimester, along with screening for anemia in the first trimester and again at 24 to 28 weeks.
The US Preventive Services Task Force, in a final recommendation dated August 20, 2024, assigned an I grade to both screening and routine supplementation in asymptomatic pregnant adolescents and adults. An I grade records that the available studies left the Task Force unable to decide whether the benefits outweigh the harms. It is explicitly not a recommendation against either practice, and the Task Force says clinicians should use clinical judgment in the absence of evidence.
That statement also carves out who it does not cover: people who are severely malnourished, who have symptoms of iron deficiency or anemia, or who have conditions such as sickle cell disease. Iron’s strongest evidence sits in documented deficiency, and nobody disputes it there.
The federal numbers show why the question is hard. The Office of Dietary Supplements estimates that 10 to 16 percent of US women have iron deficiency during pregnancy, rising to roughly 25 percent in the third trimester. It also reports that 27.9 percent of pregnant women exceed the upper limit once supplements are added to food. The Food and Nutrition Board set that limit at 45 milligrams a day for everyone aged 14 and over, pregnancy included, and ODS says it covers iron from food and supplements together.
The agency’s own summary is unusually direct: “These findings suggest a U-shaped risk of adverse health effects with both iron deficiency and iron excess.” Both ends of that curve are real, which is why expert groups land in different places. We are not resolving it, and neither has the field.
Preformed vitamin A
This one reverses the usual direction. More is not neutral, and the form matters more than the amount. A 1995 study in the New England Journal of Medicine followed 22,748 pregnant women screened between October 1984 and June 1987. Among their babies, 339 had birth defects and 121 of those involved sites that originate in the cranial neural crest, the tissue that forms much of the face and skull.
Women consuming more than 15,000 IU a day of preformed vitamin A from food and supplements combined had a prevalence ratio of 3.5 for those defects, with a confidence interval of 1.7 to 7.3, compared with women at 5,000 IU or less. From supplements alone, above 10,000 IU a day, the ratio was 4.8. The authors found an apparent threshold near 10,000 IU a day of supplemental vitamin A, and estimated that about 1 infant in 57 born to women above it had a malformation attributable to the supplement.
The Office of Dietary Supplements, in its vitamin A fact sheet updated March 10, 2025, sets the pregnancy upper limit at 2,800 mcg RAE for ages 14 to 18 and 3,000 mcg RAE for 19 and over, covering preformed vitamin A from food and supplements together. Three thousand mcg RAE is roughly 10,000 IU, so a 1995 epidemiological threshold and a current federal limit point at the same number from different directions.
Then comes the distinction that keeps readers from avoiding the wrong foods. The agency writes: “Unlike preformed vitamin A, beta-carotene is not known to be teratogenic or lead to reproductive toxicity.”
Carrots and sweet potatoes are not the issue. Retinol and its ester forms are, and those are what the upper limit is written about.
The newborn case that is not like the others
Every other item here involves a product someone chooses to buy. Vitamin K at birth does not, and that is what makes it the clearest case in this subject.
CDC describes three forms of vitamin K deficiency bleeding. Early onset occurs within the first 24 hours after birth, the classical form between two days and one week, and late onset between one week and six months, most commonly between two and eight weeks.
The agency gives early and classical bleeding as occurring in 1 in 60 to 1 in 250 newborns, and late bleeding in 1 in 14,000 to 1 in 25,000 infants. In late cases, CDC reports bleeding within the brain in 30 to 60 percent of affected infants.
The number that distinguishes this case from everything else is the comparison. CDC states that infants who do not receive a vitamin K shot at birth are 81 times more likely to develop late bleeding than infants who do.
That comparison exists because some parents decline. It is not a randomized trial, and nobody would run one now. It is a natural experiment produced by a choice, measured at national scale.
It also marks a situation that is not a supplement question at all. An infant who did not receive the injection, in that two-to-eight-week window, with unexplained bruising, bleeding from the nose or gums, or blood in a stool, needs emergency care rather than a product.
The American Academy of Pediatrics has recommended the injection since 1961. Its parent-facing guidance describes a shot given in the baby’s thigh within six hours of birth, and notes that exclusively breastfed babies carry higher risk.
Four things make this unlike the rest of the article. It prevents a bleeding disorder rather than correcting a dietary shortfall. It is given once, not daily. The amount is set by a clinician. And the question parents face is yes or no, not which product.
The first year, and then childhood
Infant vitamin D
CDC’s guidance for health professionals, last reviewed September 23, 2025, states that breastfed and partially breastfed infants should receive 400 International Units of vitamin D daily, starting in the first few days of life. Under 12 months the figure is 400 IU a day; from 12 to 24 months it is 600 IU.
CDC frames it the other way round: it says partially breastfed infants consuming less than 32 ounces of infant formula a day need an additional source of vitamin D. Which side of that line a particular baby falls on, and what follows, is a question for the pediatrician rather than an inference from the page.
Note the attribution. CDC credits this recommendation to the Dietary Guidelines for Americans and the American Academy of Pediatrics rather than to its own analysis.
Note also what CDC’s page does not say. It gives no guidance on excess intake and none on how concentrated a particular infant product is. Liquid vitamin D for infants is sold at different strengths, so the same dropperful can deliver different amounts. Matching a published figure to an actual product is a conversation with a pediatrician, not something a label settles.
Children and teenagers
The American Academy of Pediatrics position, last updated February 18, 2025, is that healthy children on a normal, well-balanced diet do not need vitamin supplementation beyond the recommended allowances. Its vitamin D reference figures are 400 IU a day under age 1 and 600 IU over age 1.
The Academy warns that megadoses of vitamins, naming A, C and D, can produce toxic symptoms ranging from nausea and rashes to headaches and more serious problems. It names no group of healthy children who should supplement.
Set that beside what children are swallowing. Pediatric melatonin ingestions reported to US poison centers climbed steeply through the 2010s, two children died, and the market expanded alongside the call volume. Article 325 carries the CDC counts, the share of all pediatric ingestions and the sales figures. The mismatch is the point: the pediatric supplement category that grew fastest is one no pediatric body recommends for healthy children.
Creatine and adolescents is a separate and genuinely unsettled question, including the state laws now restricting some sales to minors. Article 339 covers it.
Older adults: one real absorption problem, one real swallowing problem
Vitamin B12 is the strongest absorption case here, and the mechanism is worth understanding. B12 in food arrives bound to protein. The Office of Dietary Supplements, in a fact sheet updated July 2, 2025, describes hydrochloric acid and gastric protease in the stomach releasing it from that food matrix. Intrinsic factor, a binding protein secreted by the stomach’s parietal cells, then carries it onward.
Atrophic gastritis interrupts both steps. The agency describes it as an autoimmune condition affecting 2 percent of the general population but 8 to 9 percent of adults aged 65 and older, which decreases production of intrinsic factor and secretion of hydrochloric acid.
The agency also names the other groups at risk: people with pernicious anemia or gastrointestinal disorders, people who have had gastrointestinal surgery, people following vegetarian diets, and infants of women following vegan diets. In those groups B12 status is something a clinician measures, and the result changes the answer.
How common is the resulting deficiency? The agency gives a range of 3 to 43 percent of community-dwelling older adults, depending on the definition used. That spread is what happens when prevalence depends on where a threshold is drawn.
A 2021 study in the American Journal of Clinical Nutrition measured it in 3,299 non-institutionalized adults aged 60 and over who were not taking B12 supplements, recruited between 2008 and 2012. Atrophic gastritis appeared in 15 percent. In that group, B12 deficiency prevalence was 38 percent, against 21 percent in proton pump inhibitor users and 15 percent in controls.
The same study explains why fortified foods behave differently. The crystalline B12 added to them does not require gastric acid for absorption. Regular consumption tracked with better B12 biomarkers, but it was not enough to restore normal status in people with atrophic gastritis. Proton pump inhibitors sit on the boundary with drug interactions, which article 677 covers.
This age group also has a physical problem with supplements that gets almost no attention. A 2015 study in the New England Journal of Medicine used surveillance from 63 emergency departments between 2004 and 2013 to estimate 23,005 emergency visits a year for supplement-related adverse events. Among adults 65 and older, choking or pill-induced swallowing difficulty caused 37.6 percent of those visits, and micronutrients were implicated in 83.1 percent of them.
That is a problem with the physical object, not the ingredient, and it is the one finding here that argues for thinking about tablet size before thinking about contents.
Who is at risk from contaminated products
Contamination risk is concentrated in product categories, not spread evenly across people. A 2004 international study analyzed 634 non-hormonal nutritional supplements bought between October 2000 and November 2001 in 13 countries, from 215 suppliers. Of those, 94, or 14.8 percent, contained anabolic androgenic steroids not declared on the label. Among products bought in the USA the figure was 18.8 percent.
The supplier mattered more than the country: products from companies that also sold prohormones were positive 21.1 percent of the time, against 9.6 percent for companies that did not. Those purchases are now more than two decades old. The modern picture comes from a 2018 analysis in JAMA Network Open of FDA’s database of tainted products. From 2007 through 2016 it identified 776 adulterated supplements from 146 companies, most marketed for sexual improvement (45.5 percent), weight loss (40.9 percent) or muscle building (11.9 percent). Synthetic steroids turned up in 89.1 percent of the adulterated muscle-building products.
Athletes are exposed because those categories overlap with what performance marketing sells, not because athletes are biologically vulnerable. Articles 340 and 326 cover the mitigations: heavy metals in powders and third-party verification marks.
One honest gap. We looked for evidence that pregnant or breastfeeding people face a documented, pregnancy-specific risk from contaminated supplements and found no source establishing it. The well-documented pregnancy risk here comes from intended ingredients at high doses, which is the vitamin A evidence above.
Five questions that decide whether a recommendation is about you
Most confusion here comes from applying a real finding to the wrong person. These five questions sort that out, and they work on any claim you meet.
Which population was studied? The 1991 folic acid trial enrolled women who had already had an affected pregnancy. The 1992 trial enrolled women who had not. Same nutrient, two questions, two answers.
Is the number an allowance, an upper limit, or a trial dose? Those are three different kinds of figure, and swapping them is the most common error in supplement writing.
Does the recommendation have a timing window? Folic acid’s opens before conception. Vitamin K’s is six hours wide. A recommendation with a deadline is not the same as a standing one.
Does it name an exception that includes you? The infant vitamin D guidance names babies taking less than 32 ounces of formula a day. The iron statement excludes anyone with symptoms or a documented condition. Exceptions are where most readers live.
Who decides the amount? For newborn vitamin K and for treating a documented deficiency, a clinician does. That is a different situation from choosing a product yourself.
The pattern worth carrying away is this. The best evidence in this field clusters in narrow windows near the beginning of life, in populations defined by a specific risk, and in amounts set by somebody with your test results in front of them. Almost none of it was generated in the decades where supplement use is highest.
Sources
- National Center for Health Statistics, CDC. “Dietary Supplement Use: United States, August 2021-August 2023 (NCHS Data Brief No. 561, May 2026).” cdc.gov
- Centers for Disease Control and Prevention. “Dietary Supplement Use in Children and Adolescents Aged <=19 Years – United States, 2017-2018 (MMWR, October 30, 2020).” cdc.gov
- NIH Office of Dietary Supplements. “Dietary Supplements for Pregnancy – Health Professional Fact Sheet.” ods.od.nih.gov
- NIH Office of Dietary Supplements. “Vitamin A and Carotenoids – Health Professional Fact Sheet (updated March 10, 2025).” ods.od.nih.gov
- NIH Office of Dietary Supplements. “Vitamin B12 – Health Professional Fact Sheet (updated July 2, 2025).” ods.od.nih.gov
- US Preventive Services Task Force. “Folic Acid Supplementation to Prevent Neural Tube Defects: Final Recommendation Bulletin (August 1, 2023, Grade A).” uspreventiveservicestaskforce.org
- US Preventive Services Task Force. “Iron Deficiency and Iron Deficiency Anemia During Pregnancy: Screening and Supplementation (final recommendation, August 20, 2024).” uspreventiveservicestaskforce.org
- Centers for Disease Control and Prevention. “Vitamin D and Breastfeeding (last reviewed September 23, 2025).” cdc.gov
- Centers for Disease Control and Prevention. “About Vitamin K Deficiency Bleeding (last reviewed January 17, 2025).” cdc.gov
- American Academy of Pediatrics (HealthyChildren.org). “Why Your Newborn Needs a Vitamin K Injection.” healthychildren.org
- American Academy of Pediatrics (HealthyChildren.org). “Where We Stand: Vitamins (last updated February 18, 2025).” healthychildren.org
- PubMed. “Rothman KJ, Moore LL, Singer MR, Nguyen US, Mannino S, Milunsky A. "Teratogenicity of high vitamin A intake." New England Journal of Medicine, 1995. PubMed. DOI: 10.1056/NEJM199511233332101.” doi.org
- PubMed. “MRC Vitamin Study Research Group. "Prevention of neural tube defects: results of the Medical Research Council Vitamin Study." Lancet, 1991. PubMed. PMID: 1677062.” pubmed.ncbi.nlm.nih.gov
- PubMed. “Czeizel AE, Dudas I. "Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation." New England Journal of Medicine, 1992. PubMed. DOI: 10.1056/NEJM199212243272602.” doi.org
- PubMed. “Porter KM et al. "Associations of atrophic gastritis and proton-pump inhibitor drug use with vitamin B-12 status, and the impact of fortified foods, in older adults." American Journal of Clinical Nutrition, 2021. PubMed. DOI: 10.1093/ajcn/nqab193.” doi.org
- PubMed. “Geller AI et al. "Emergency Department Visits for Adverse Events Related to Dietary Supplements." New England Journal of Medicine, 2015. PubMed. DOI: 10.1056/NEJMsa1504267.” doi.org
- PubMed. “Geyer H, Parr MK, Mareck U, Reinhart U, Schrader Y, Schanzer W. "Analysis of non-hormonal nutritional supplements for anabolic-androgenic steroids: results of an international study." International Journal of Sports Medicine, 2004. PubMed. DOI: 10.1055/s-2004-819955.” doi.org
- PubMed. “Lelak K, Vohra V, Neuman MI, Toce MS, Sethuraman U. "Pediatric Melatonin Ingestions: United States, 2012-2021." MMWR, 2022. PubMed. DOI: 10.15585/mmwr.mm7122a1.” doi.org
- PubMed. “Tucker J, Fischer T, Upjohn L, Mazzera D, Kumar M. "Unapproved Pharmaceutical Ingredients Included in Dietary Supplements Associated With US Food and Drug Administration Warnings." JAMA Network Open, 2018. PubMed. DOI: 10.1001/jamanetworkopen.2018.3337.” doi.org