--- topic: "Supplement Basics" title: "Do You Need a Supplement?" order: 1 description: "How to decide whether a vitamin or mineral supplement is worth taking: food first, which blood test answers which question, the groups with a proven need, and what the big multivitamin trials found for everyone else." question: "Do you need a vitamin or mineral supplement, and how can you tell?" answer: "Most healthy adults who eat varied food probably gain little from supplements; pregnancy, vegan diets, older age, breastfed infants and some medicines create real needs." actions: - "Could you become pregnant? The US Preventive Services Task Force recommends a daily supplement with 400 to 800 micrograms of folic acid [7]." - "Breastfeeding, fully or partly? Pediatricians advise 400 IU of vitamin D drops a day for the baby, starting soon after birth [10]." - "Vegan, or over 50? Get vitamin B12 from fortified foods or a supplement: plant foods lack it, and many older people absorb food B12 poorly [14][15]." cautions: - "Taking metformin, or an acid-reducing medicine for two years or more? Ask about a B12 test, and magnesium with proton pump inhibitors, instead of guessing [22][24][26]." - "Pregnant or planning? Choose a prenatal with iodine, and keep preformed vitamin A (retinol) from supplements under 10,000 IU a day [8][28]." - "Thinking of iron for tiredness? Get ferritin checked first: iron helped tired women with low stores, but people with hemochromatosis must avoid it [20][21]." confidence: 4 confidenceNote: "Long randomized trials found little or no benefit from multivitamins in well-fed adults; the needs of specific groups rest on task-force reviews, randomized trials and deficiency surveys." evidenceSummary: rctCount: 6 observationalCount: 5 metaAnalysisCount: 1 totalParticipants: "390,000+" replicated: true newestStudyYear: 2026 references: - id: "1" pmid: "30959527" title: "Association Among Dietary Supplement Use, Nutrient Intake, and Mortality Among U.S. Adults: A Cohort Study" authors: "Chen F, Du M, Blumberg JB, et al." year: 2019 journal: "Annals of Internal Medicine" - id: "2" pmid: "35727271" title: "Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: US Preventive Services Task Force Recommendation Statement" authors: "Mangione CM, Barry MJ, Nicholson WK, et al." year: 2022 journal: "JAMA" - id: "3" pmid: "23117775" title: "Multivitamins in the prevention of cardiovascular disease in men: the Physicians' Health Study II randomized controlled trial" authors: "Sesso HD, Christen WG, Bubes V, et al." year: 2012 journal: "JAMA" - id: "4" pmid: "23162860" title: "Multivitamins in the prevention of cancer in men: the Physicians' Health Study II randomized controlled trial" authors: "Gaziano JM, Sesso HD, Christen WG, et al." year: 2012 journal: "JAMA" - id: "5" pmid: "35294969" title: "Multivitamins in the prevention of cancer and cardiovascular disease: the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized clinical trial" authors: "Sesso HD, Rist PM, Aragaki AK, et al." year: 2022 journal: "American Journal of Clinical Nutrition" - id: "6" pmid: "38922615" title: "Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts" authors: "Loftfield E, O'Connell CP, Abnet CC, et al." year: 2024 journal: "JAMA Network Open" - id: "7" pmid: "37526713" title: "Folic Acid Supplementation to Prevent Neural Tube Defects: US Preventive Services Task Force Reaffirmation Recommendation Statement" authors: "Barry MJ, Nicholson WK, Silverstein M, et al." year: 2023 journal: "JAMA" - id: "8" url: "https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/" title: "Iodine: Fact Sheet for Health Professionals" authors: "NIH Office of Dietary Supplements" year: 2024 journal: "NIH Office of Dietary Supplements" - id: "9" url: "https://ods.od.nih.gov/factsheets/Choline-HealthProfessional/" title: "Choline: Fact Sheet for Health Professionals" authors: "NIH Office of Dietary Supplements" year: 2022 journal: "NIH Office of Dietary Supplements" - id: "10" pmid: "18977996" title: "Prevention of rickets and vitamin D deficiency in infants, children, and adolescents" authors: "Wagner CL, Greer FR" year: 2008 journal: "Pediatrics" - id: "11" url: "https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/" title: "Vitamin D: Fact Sheet for Health Professionals" authors: "NIH Office of Dietary Supplements" year: 2025 journal: "NIH Office of Dietary Supplements" - id: "12" pmid: "38828931" title: "Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline" authors: "Demay MB, Pittas AG, Bikle DD, et al." year: 2024 journal: "Journal of Clinical Endocrinology and Metabolism" - id: "13" pmid: "33847711" title: "Screening for Vitamin D Deficiency in Adults: US Preventive Services Task Force Recommendation Statement" authors: "Krist AH, Davidson KW, Mangione CM, et al." year: 2021 journal: "JAMA" - id: "14" url: "https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/" title: "Vitamin B12: Fact Sheet for Health Professionals" authors: "NIH Office of Dietary Supplements" year: 2025 journal: "NIH Office of Dietary Supplements" - id: "15" url: "https://nap.nationalacademies.org/read/6015/chapter/11" title: "Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline: Chapter 9, Vitamin B12" authors: "Institute of Medicine, Food and Nutrition Board" year: 1998 journal: "National Academies Press" - id: "16" pmid: "23356638" title: "How prevalent is vitamin B(12) deficiency among vegetarians?" authors: "Pawlak R, Parrott SJ, Raj S, et al." year: 2013 journal: "Nutrition Reviews" - id: "17" pmid: "24679552" title: "Blood docosahexaenoic acid and eicosapentaenoic acid in vegans: Associations with age and gender and effects of an algal-derived omega-3 fatty acid supplement" authors: "Sarter B, Kelsey KS, Schwartz TA, Harris WS" year: 2015 journal: "Clinical Nutrition" - id: "18" url: "https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/" title: "Omega-3 Fatty Acids: Fact Sheet for Health Professionals" authors: "NIH Office of Dietary Supplements" year: 2025 journal: "NIH Office of Dietary Supplements" - id: "19" pmid: "15208005" title: "The Omega-3 Index: a new risk factor for death from coronary heart disease?" authors: "Harris WS, Von Schacky C" year: 2004 journal: "Preventive Medicine" - id: "20" url: "https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/" title: "Iron: Fact Sheet for Health Professionals" authors: "NIH Office of Dietary Supplements" year: 2025 journal: "NIH Office of Dietary Supplements" - id: "21" pmid: "22777991" title: "Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial" authors: "Vaucher P, Druais PL, Waldvogel S, Favrat B" year: 2012 journal: "CMAJ" - id: "22" pmid: "26900641" title: "Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study" authors: "Aroda VR, Edelstein SL, Goldberg RB, et al." year: 2016 journal: "Journal of Clinical Endocrinology and Metabolism" - id: "23" pmid: "20488910" title: "Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial" authors: "de Jager J, Kooy A, Lehert P, et al." year: 2010 journal: "BMJ" - id: "24" pmid: "24327038" title: "Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency" authors: "Lam JR, Schneider JL, Zhao W, Corley DA" year: 2013 journal: "JAMA" - id: "25" pmid: "26108134" title: "Proton pump inhibitors linked to hypomagnesemia: a systematic review and meta-analysis of observational studies" authors: "Cheungpasitporn W, Thongprayoon C, Kittanamongkolchai W, et al." year: 2015 journal: "Renal Failure" - id: "26" url: "https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/" title: "Magnesium: Fact Sheet for Health Professionals" authors: "NIH Office of Dietary Supplements" year: 2026 journal: "NIH Office of Dietary Supplements" - id: "27" pmid: "39163015" title: "Screening and Supplementation for Iron Deficiency and Iron Deficiency Anemia During Pregnancy: US Preventive Services Task Force Recommendation Statement" authors: "Nicholson WK, Silverstein M, Wong JB, et al." year: 2024 journal: "JAMA" - id: "28" pmid: "7477116" title: "Teratogenicity of high vitamin A intake" authors: "Rothman KJ, Moore LL, Singer MR, et al." year: 1995 journal: "New England Journal of Medicine" --- In healthy adults, the largest trials of daily multivitamins found little or no protection against heart disease, cancer or early death, and nutrients from food, not pills, went with longer life [1][3][5][6]. Supplements earn their place for a known gap: folic acid if you could become pregnant, vitamin D drops for breastfed babies, B12 for vegans and many older adults, iron when stores are low [7][10][15][16][21]. When unsure, the right blood test beats a guess. ## How it works **Start with food.** In a study that followed 30,899 US adults for about six years, getting enough vitamin A, vitamin K, magnesium, zinc and copper went with lower death rates only when the nutrients came from food, and taking supplements did not go with longer life [1]. That study was observational, but it points the same way as the trials below. **What the multivitamin trials found for everyone else.** The US Preventive Services Task Force (USPSTF) found too little evidence to say whether a multivitamin prevents heart disease or cancer, and it advises against beta-carotene and vitamin E supplements for that purpose [2]. In the Physicians' Health Study II, 14,641 male doctors took a multivitamin or a placebo for a median of 11.2 years: heart attacks and strokes did not fall [3], and total cancer was 8% lower [4]. In COSMOS, 21,442 older adults saw no effect on cancer, heart disease or death [5], and among 390,124 adults followed for up to 27 years, multivitamin users did not live longer [6]. Our article on [multivitamins](/multivitamins/should-you-take-a-multivitamin) goes further. **Test before you take.** For several nutrients, a blood test can answer the question directly: | What you want to know | The test | How it is read | |---|---|---| | Am I low in vitamin D? | 25-hydroxyvitamin D, written 25(OH)D | 50 nmol/L (20 ng/mL) or more is enough for most people; under 30 nmol/L (12 ng/mL) raises the risk of deficiency; over 125 nmol/L (50 ng/mL) is linked to possible harm [11] | | Am I low in B12? | Serum B12, plus methylmalonic acid (MMA) when B12 is borderline | B12 under 200 to 250 pg/mL is usually called low; MMA is the most sensitive marker and confirms a deficiency when B12 is between 150 and 399 pg/mL [14] | | Are my iron stores low? | Ferritin, with a blood count | Ferritin measures stored iron, but inflammation can distort it, so it is read alongside other results [20] | | Do I get enough omega-3? | Omega-3 index: EPA plus DHA in red blood cells | Reflects roughly the last four months of intake [18]; researchers who proposed it linked 8% or more with the lowest risk of heart death and 4% or less with the highest [19] | Two limits. Guideline panels do not advise testing everyone for vitamin D: the Endocrine Society suggests against routine 25(OH)D tests in healthy people, including those with obesity or darker skin, and the USPSTF found too little evidence to screen adults without symptoms [12][13]. And some tests answer the question poorly: blood magnesium, for instance, says little about how much magnesium the body holds [26]. Your clinician can order these tests, and several are sold by the [direct-to-consumer lab services](/products/category/health-testing) we review, which we judge on the lab behind them and who reads your results. **Who has a real need.** The groups below have evidence behind them, not just marketing: - **Planning a pregnancy, or could become pregnant:** folic acid, 400 to 800 micrograms a day, which the USPSTF gives its top grade [7]; iodine, 150 micrograms a day as potassium iodide on American Thyroid Association advice, which not every prenatal contains [8]; and enough choline, which most prenatal supplements barely provide [9]. See [eating well during pregnancy](/pregnancy-nutrition/eating-well-during-pregnancy). - **Breastfeeding:** the same iodine advice applies [8], and vegan mothers need a reliable B12 source, because their babies can become deficient very early [14]. - **Breastfed babies:** 400 IU (10 micrograms) of vitamin D a day from soon after birth, until the baby drinks at least 1,000 mL (about a quart) of fortified formula or whole milk a day; breast milk alone does not supply enough [10][11]. - **Over 50:** many older people absorb the B12 in food poorly, so the National Academies advise getting it mainly from fortified foods or a supplement [15]. From 75, the Endocrine Society suggests vitamin D beyond the standard intake [12]. See [who needs B12](/vitamin-b12/neurological-energy-and-who-needs-it). - **Vegans:** B12 is not optional [16]; iodine can run short without dairy, seafood or eggs [8]; and an algae oil is the plant source of ready-made EPA and DHA, because the body converts little of the omega-3 in foods such as flaxseed [17][18]. See [vegan and vegetarian diets](/plant-based-diet/are-vegan-and-vegetarian-diets-healthy). - **Heavy periods, low ferritin or frequent blood donation:** iron, after a test [20][21]. See [iron basics](/iron/iron-basics). - **Little sun:** vitamin D intakes are set on the assumption of minimal sun, and people with little sun exposure or darker skin are more likely to run low [11]. See [vitamin D supplementation](/vitamin-d/supplementation). - **Long-term metformin or acid-reducing medicine:** B12 can fall, and so can magnesium with proton pump inhibitors [22][24][25]. See [which medicines deplete nutrients](/medication-nutrient-depletion/which-medications-deplete-nutrients). Decided you need something? Check [how much is too much](/supplement-basics/how-much-is-too-much) before you buy, read [what to skip](/supplement-basics/supplements-to-skip), then use the [supplement schedule](/schedule) for when to take it. ## The evidence in detail ### Multivitamins in well-nourished adults The Physicians' Health Study II randomized 14,641 male US physicians aged 50 or older (mean age 64.3) to a daily multivitamin or placebo. Over a median of 11.2 years there was no effect on major cardiovascular events (HR 1.01, 95% CI 0.91–1.10) or total mortality (HR 0.94, 95% CI 0.88–1.02) [3]. Total cancer was modestly lower (17.0 versus 18.3 cases per 1,000 person-years; HR 0.92, 95% CI 0.86–0.998), with no effect on prostate or colorectal cancer and no significant change in cancer deaths (HR 0.88, 95% CI 0.77–1.01) [4]. COSMOS randomized 21,442 US adults (women aged 65 or older, men aged 60 or older) to a multivitamin-multimineral or placebo. Over a median of 3.6 years, invasive cancer (HR 0.97, 95% CI 0.86–1.09), cardiovascular events (HR 0.98, 95% CI 0.86–1.12) and all-cause mortality (HR 0.93, 95% CI 0.81–1.08) did not differ. Lung cancer was lower (HR 0.62, 95% CI 0.42–0.92), a secondary finding [5]. Because the trials had limited follow-up, a 2024 cohort study pooled 390,124 adults without chronic disease from three US cohorts, with up to 27 years of follow-up and 164,762 deaths. Daily multivitamin use was not linked to lower mortality (HR 1.04, 95% CI 1.02–1.07 in the first half of follow-up; HR 1.04, 95% CI 0.99–1.08 in the second) [6]. Users were more often women and college educated and less often smokers, a reminder that people who take supplements differ from those who do not. The USPSTF weighed this evidence in 2022. It issued an I statement (insufficient evidence) for multivitamins and for single or paired nutrients other than beta-carotene and vitamin E, and a D recommendation (against) for those two, for preventing cardiovascular disease or cancer. At the time, 52% of US adults reported using at least one supplement and 31% a multivitamin-mineral [2]. The food comparison comes from 30,899 adults in the National Health and Nutrition Examination Survey (NHANES), followed for a median of 6.1 years (3,613 deaths). Ever-use of supplements was not associated with mortality. Adequate intakes of vitamin A, vitamin K, magnesium, zinc and copper were associated with lower all-cause or cardiovascular mortality, but only when they came from food [1]. Calcium from supplements at 1,000 mg a day or more was associated with more cancer deaths (rate ratio 1.53, 95% CI 1.04–2.25) [1]. Residual confounding and recall bias are possible in a study like this. All of these studies enrolled mostly well-nourished US adults; none tested people with a known deficiency. ### What guideline panels say about testing The 2024 Endocrine Society guideline found no trial evidence to support routine 25(OH)D screening in the general population, including people with obesity or a dark complexion, and no clear evidence for an optimal blood level, so it suggests against routine testing [12]. The same panel suggests vitamin D beyond the dietary reference intake for ages 1 to 18, adults over 75, pregnancy and high-risk prediabetes, and against it for healthy adults under 75; it calls the best doses unclear [12]. The USPSTF noted that no single blood level defines deficiency and gave screening of adults without symptoms an I statement [13]. The cut-offs in the table come from the Food and Nutrition Board for vitamin D [11], and from laboratory practice for B12 and MMA, where an MMA above 0.271 micromol/L suggests deficiency [14]. Ferritin reflects iron stores but can be affected by inflammation, and hemoglobin is neither sensitive nor specific, so clinicians often combine measures [20]. Red-cell fatty acids reflect about 120 days of intake, while plasma levels swing with the last meal [18]. The omega-3 index was proposed by its developers as a heart-risk marker: in their analysis an index of 8% or more went with the greatest protection and 4% or less with the least [19]. ### Pregnancy and infancy The USPSTF concluded with high certainty that folic acid has a substantial net benefit and recommends 0.4 to 0.8 mg (400 to 800 micrograms) a day for anyone planning or able to become pregnant (grade A); about 3,000 US pregnancies a year are affected by neural tube defects [7]. For iodine, the American Thyroid Association advises 150 micrograms a day as potassium iodide for anyone planning a pregnancy, pregnant or breastfeeding, and the American Academy of Pediatrics advises at least 150 micrograms plus iodized salt; of 59 best-selling prenatal supplements in 2016 to 2017, only 34 contained iodine [8]. About 90% to 95% of pregnant women take in less choline than the adequate intake of 450 mg a day, and prenatal supplements typically contain little or none [9]. Iron needs rise in pregnancy (the RDA is 27 mg a day) [20]. Yet the USPSTF found the evidence insufficient to judge either screening or routine iron supplementation in pregnant people without symptoms, although iron deficiency affects about 18% of pregnancies and rises from 6.9% to 28.4% between the first and third trimesters [27]. That is a question for your prenatal care team rather than a reason to add iron on your own. Preformed vitamin A needs a ceiling. Among 22,748 pregnant women, those taking more than 10,000 IU a day from supplements had 4.8 times the rate of cranial-neural-crest birth defects seen with 5,000 IU or less (95% CI 2.2–10.5), mostly when exposure came before the seventh week; the authors estimated that about 1 in 57 exposed babies had a malformation caused by the supplement [28]. That was a single observational cohort; its apparent threshold, near 10,000 IU a day of supplemental vitamin A, is the same as the adult upper limit in [how much is too much](/supplement-basics/how-much-is-too-much). For infants, the American Academy of Pediatrics raised its advice to at least 400 IU of vitamin D a day for all infants, including those exclusively breastfed, starting soon after birth [10]. Human milk provides only about 25 to 78 IU per liter, and the advice lasts until a baby drinks at least 1,000 mL a day of vitamin D-fortified formula or whole milk [11]. ### B12: age, diet and medicines The National Academies estimated that 10% to 30% of older people may be unable to absorb the B12 naturally present in food, while absorption of the crystalline B12 used in fortified foods and supplements does not appear to fall with age; hence the advice that people over 50 meet their needs mainly from those sources [15]. Atrophic gastritis, which cuts the acid and intrinsic factor needed to absorb food B12, affects 2% of the general population but 8% to 9% of adults aged 65 and older [14]. A review of 18 studies that measured deficiency with MMA or holotranscobalamin found it in 62% of pregnant vegetarian women, 25% to almost 86% of children, 21% to 41% of adolescents and 11% to 90% of older adults, with higher rates in vegans and in people vegetarian since birth [16]. Fortified foods and supplements substantially reduce the risk [14]. In a randomized trial in the Netherlands, 390 people with type 2 diabetes on insulin took metformin 850 mg three times a day or placebo for 4.3 years; B12 ended 19% lower than with placebo, and the absolute risk of deficiency was 7.2 percentage points higher, a number needed to harm of 13.8 [23]. In the Diabetes Prevention Program Outcomes Study, low B12 was more common with metformin at 5 years (4.3% versus 2.3%), low or borderline B12 at 5 and 13 years (19.1% versus 9.5%, and 20.3% versus 15.6%), and each year of use raised the odds (OR 1.13, 95% CI 1.06–1.20) [22]. Both teams suggested regular B12 checks. In a case-control study in Kaiser Permanente Northern California, 25,956 people with B12 deficiency were compared with 184,199 without: two or more years of proton pump inhibitors (OR 1.65, 95% CI 1.58–1.73) or H2 blockers (OR 1.25, 95% CI 1.17–1.34) were associated with deficiency [24]. For magnesium, a meta-analysis of nine observational studies (109,798 patients) found a pooled risk ratio of 1.43 (95% CI 1.08–1.88) with proton pump inhibitors [25]. The FDA advises clinicians to consider checking magnesium before and periodically during long-term use; in a quarter of the cases it reviewed, supplements did not correct the low level and the drug had to be stopped [26]. ### Iron: when it helps and when it harms A trial in France randomized 198 menstruating women aged 18 to 53 with unexplained fatigue, ferritin under 50 µg/L and normal hemoglobin to 80 mg of elemental iron a day or placebo for 12 weeks. Fatigue scores fell by 47.7% with iron and 28.8% with placebo (difference −18.9%, 95% CI −34.5 to −3.2), with no change in quality of life, depression or anxiety, and ferritin rose 11.4 µg/L more than with placebo [21]. The authors suggest checking blood markers after six weeks [21]. Iron is not harmless when stores are full: about 1 in 10 white people carry the most common hemochromatosis gene variant and about 4.4 per 1,000 have two copies, and liver specialists advise people with hemochromatosis to avoid iron and vitamin C supplements [20]. People on vegetarian diets need about 1.8 times as much iron, because plant iron is absorbed less well [20]. ### Omega-3 for vegans Among 165 long-term vegans, the mean omega-3 index was 3.7%, similar to omnivores who get very little EPA and DHA [17]. In 46 with an index below 4%, an algae-derived supplement giving 254 mg of EPA plus DHA a day for 4 months raised the index from 3.1% to 4.8% [17]. That study measured blood levels, not health outcomes. The body converts less than 15% of plant omega-3 (ALA) into EPA and DHA [18]. ### Bottom line (confidence 4 of 5) For well-nourished adults, long randomized trials found little benefit from a daily multivitamin, and a very large cohort points the same way. Real needs in pregnancy, infancy, older age, vegan diets, low iron stores and long-term metformin or acid-reducer use rest on task-force reviews, randomized trials and deficiency surveys. Testing helps when there is a reason to suspect a gap; for vitamin D, guideline panels advise against routine testing of healthy people. None of this replaces advice from your own clinician or pharmacist, especially if you are pregnant, take prescription medicines or have a chronic condition.