Verified Supplement Data Primary-sourced

Best Supplements for Women by Life Stage, Ranked by Evidence

By Erin Rose · Published · Reviewed against primary sources · Methodology · About Us

Informational summary of published trials, guidelines and NIH label data, not medical advice. In pregnancy, while breastfeeding, or with kidney disease or a diagnosed deficiency, the clinician managing your care decides any dose.

Quick answer

Three supplements have strong evidence for women, and each is tied to a stage rather than to being female. Iron if you menstruate and a ferritin test is low. Folic acid at 400–800 mcg if you could become pregnant, the only A-grade recommendation here. Vitamin D if you test low, with a case for going above the RDA in pregnancy. After those, the ranking turns on who you are: choline and DHA in pregnancy, calcium and creatine after menopause, collagen for skin. “Hormone balance” and “hair, skin and nails” blends sit in the hopeful tier.

The women’s aisle is dosed for the shopper, not the trial. From the label censuses behind our women’s guides: 72.1% of prenatals carry under 1,000 IU of vitamin D, 14.3% of women’s probiotics name the strains with vaginal trials, creatine HCl sits at a median 2 g against 5 g for monohydrate, and 70.8% of collagen capsules direct less than the 2.5 g skin dose. See what the aisle sells →

Women 31–50 with ferritin under 1210.5%vs 0.3% of men · NHANES
Folic acid · USPSTF gradeA400–800 mcg if you could conceive
The core three $0.28 per day, our catalog picks

Over 50? The stack for adults over 50 covers the age-driven changes that apply to either sex.

On this page
  1. The ranked table
  2. Menstruating
  3. Trying or pregnant
  4. Breastfeeding
  5. Perimenopause
  6. After menopause
  7. The multivitamin question
  8. The hopeful tier
  9. What to test first
  10. What it costs
  11. FAQ

Eleven supplements sold to women, ranked by the strength of their evidence

Ordered by the size and quality of the randomized trials in women; outside the “who” column the grade usually drops to null. Cost is our catalog pick at the studied dose. Each row links to its section, and each section to the deep guide.

Supplements for women ranked by trial evidence: who each applies to, the studied dose, our pick and its cost per day at that dose. Prices reviewed 2026-09-17.
#IngredientWhoWhat the trials sayStudied doseOur pickCost/day
1 Iron (bisglycinate) Menstruating, ferritin low Strong if low: fatigue improves even without anemia. Null if not. 18 mg/day RDA; 25–36 mg on alternate days NOW Foods Iron 36 mg Double Strength (Ferrochel) $0.10
2 Folic acid / folate Could become pregnant USPSTF grade A: fewer neural tube defects. The trials used folic acid. 400–800 mcg/day, from a month before conception Jarrow Formulas Methyl Folate 400 mcg
methylfolate, not the trial agent 		$0.13
3 Vitamin D3 Tests low; pregnancy Corrects a deficiency; null in women who already have enough. 1,000–2,000 IU/day; 4,000 IU in the pregnancy trial Nature Made Vitamin D3 2000 IU $0.05
4 Choline Pregnant One controlled-feeding trial; under one in ten pregnant women reach the AI. 450 mg/day AI; 930 mg in the trial Nutricost Choline Bitartrate 650mg
about 260 mg choline per capsule 		$0.07
5 Calcium (citrate) + D After menopause, food gap only Fracture benefit only in women low in both calcium and D. 1,200 mg/day total from 51; a 200–500 mg gap Solgar Calcium Citrate with Vitamin D3
250 mg per tablet; priced at two 		$0.18
6 Creatine monohydrate Women who lift, any age Strength real; lean mass small; nothing without training; no pregnancy trial. 3–5 g/day Optimum Nutrition Micronized Creatine Monohydrate (60 servings) $0.27
7 Omega-3 (DHA) Pregnant, little fish Fewer preterm births, high-quality evidence; no effect on infant cognition. About 200 mg DHA/day Sports Research Triple Strength Omega-3 (1250mg)
260 mg DHA per softgel; priced at one 		$0.32
8 Probiotic, by strain On antibiotics; BV add-on Antibiotic diarrhea: strong. BV: one strong trial, Cochrane says insufficient. UTI: null. 1 billion CFU each of GR-1 + RC-14 twice daily; 5 billion CFU/day or more with antibiotics Culturelle Daily Probiotic (10B CFU, 30ct)
L. rhamnosus GG, for the antibiotic course 		$0.59
9 Collagen peptides Skin, 35–65; bone after menopause Skin: instrument-measured gains. Bone: one trial. Hair: nothing. 2.5 g/day skin; 5 g bone Sports Research Collagen Peptides (Unflavored)
priced at 2.5 g 		$0.18
10 Magnesium glycinate Sleep and PMS shoppers Sleep: three small trials, low quality. PMS: insufficient. 200–400 mg elemental Vitamin Shoppe Magnesium Glycinate 400mg $0.23
11 Multivitamin Could conceive; restricted diet Insufficient for disease prevention; slower cognitive aging at a mean age of 73. One a day; iron only before menopause NATURELO One Daily Multivitamin for Women
iron-free alternative below 		$0.40

By life stage: what changes, and what does not

Most “for women” supplements are the same molecule at the same dose as for men, with a pink label. The real exceptions track life stage: menstrual iron loss, the folate window before a pregnancy is known, a fetus’s choline and DHA demand, and the calcium step-up and iron step-down at 51.

Menstruating: test ferritin, then decide about iron

Iron is the one nutrient whose requirement is set by being a woman of reproductive age: the RDA is 18 mg against 8 mg for men, and iron-deficiency anemia is concentrated in menstruating women (Tang 2024, PMID: 38042684). In CDC NHANES measurements, 9.5% of women aged 18–30 and 10.5% of women 31–50 have serum ferritin below 12 ng/mL, against 0.6% and 0.3% of men the same ages; 35.7% and 32.9% sit below 30 ng/mL, where stores count as low.

Adults with serum ferritin below 12 ng/mL, by age and sex
0% 6% 12% 18% 24% Women 18–30 35.7% below 30 ng/mL 9.5% Women 31–50 32.9% below 30 ng/mL 10.5% Women 51–65 10.7% below 30 ng/mL 2.7% Women 65+ 9.5% below 30 ng/mL 0.5% Men 18–30 2.3% below 30 ng/mL 0.6% Men 31–50 3.4% below 30 ng/mL 0.3%
10.5% of women aged 31–50 and 9.5% of women 18–30 test below 12 ng/mL, against 0.3% and 0.6% of men the same ages; the deficiency is a reproductive-years problem and it closes after menopause. Source: CDC NHANES 2017–March 2020 pre-pandemic cycle, serum ferritin, survey-weighted (n=8,360).
Adults with serum ferritin below 12 ng/mL, by age and sex
ItemValue (%)
Women 18–309.5%
Women 31–5010.5%
Women 51–652.7%
Women 65+0.5%
Men 18–300.6%
Men 31–500.3%

Low stores matter before anemia does: in 198 menstruating women with unexplained fatigue, ferritin under 50 µg/L and normal hemoglobin, 12 weeks of 80 mg of iron cut the fatigue score by 47.7% against 28.8% on placebo (Vaucher 2012, PMID: 22777991). Iron is not excreted, though, and taking it with normal stores buys nothing. So test, supplement, retest, with a bisglycinate form every other day, which absorbs a larger fraction of each dose (Stoffel 2017, PMID: 29032957). Our pick is the iron for women guide’s value pick, NOW Foods Iron 36 mg Double Strength (Ferrochel) $0.10/day.

Two smaller notes. For PMS, the 2025 review of 31 randomized trials found consistent effects for vitamin B6, calcium and zinc, and insufficient evidence for magnesium (Robinson 2025, PMID: 38684926). A probiotic earns its place during an antibiotic course: across 63 trials, probiotics cut antibiotic-associated diarrhea by 42% (Hempel 2012, PMID: 22570464). For the vaginal tract, L. rhamnosus GR-1 and L. reuteri RC-14 added to metronidazole raised the day-30 BV cure rate from 40% to 88% among 106 completers (Anukam 2006, PMID: 16697231), which Cochrane called promising and insufficient (Senok 2009, PMID: 19821358); the probiotics for women guide has the strain-by-problem table.

Trying to conceive, or pregnant: folic acid first, then vitamin D, choline and DHA

Folic acid is the clearest recommendation on this page. The neural tube closes in the first four weeks, before most pregnancies are confirmed, so the US Preventive Services Task Force recommends that everyone planning or capable of pregnancy take 400–800 mcg of folic acid daily: grade A in 2017 (Bibbins-Domingo 2017, PMID: 28097362), reaffirmed in 2023 with high certainty (US Preventive Services Task Force 2023, PMID: 37526713). Our catalog carries no plain folic-acid product: the women’s multi and the standalone pick deliver 400 mcg as methylfolate, which was not the trial agent; the methylfolate guide says not to substitute on your own reasoning. A prenatal is the standard carrier: 86.7% of the 444 prenatal labels in our census carry folate and 74.5% carry iron.

Vitamin D is where 2024 changed the answer. The Endocrine Society now suggests supplementing above the RDA in pregnancy while calling the best dose unsettled (Demay 2024, PMID: 38828931); the safety trial that randomized 494 women to 400, 2,000 or 4,000 IU found 4,000 most effective, with no adverse event attributed to any dose (Hollis 2011, PMID: 21706518). The prenatal usually does not get there: 72.1% of prenatal labels carry less than 1,000 IU and 2.6% reach the trial dose, so the top-up is a conversation for your next appointment (the vitamin D for women guide has the census).

Choline is the pregnancy nutrient the prenatal aisle forgot. The Adequate Intake in pregnancy is 450 mg, and NHANES usual-intake modelling found only 8.5% of pregnant women meet it (Wallace 2017, PMID: 28783055). In the one controlled-feeding trial, women given 930 mg a day in the third trimester, against 480, had infants with faster information-processing speed through 13 months (Caudill 2018, PMID: 29217669). One trial, a functional outcome rather than IQ, at about double the AI: any dose above food plus a prenatal is a clinician’s call (the choline in pregnancy guide).

DHA has the most specific result. The Cochrane review of 70 trials in 19,927 women found omega-3 in pregnancy lowered preterm birth before 37 weeks from 13.4% to 11.9% and early preterm birth before 34 weeks from 4.6% to 2.7%, high-quality evidence (Middleton 2018, PMID: 30480773). It does not make a smarter baby or a happier mother: 800 mg of DHA a day in the 2,399-woman DOMInO trial changed neither postpartum depression nor child cognition at 18 months (Makrides 2010, PMID: 20959577). The omega-3 dosage guide puts the target at about 200 mg of DHA a day; one softgel of our pick carries 260 mg.

Three things not to add. Creatine has no randomized trial in pregnancy; a Cochrane review looked and found none (Dickinson 2014, PMID: 25523279). Collagen has none either (the collagen for women guide). And a probiotic taken as a general pregnancy supplement points the wrong way: the Cochrane review of probiotics to prevent gestational diabetes found no clear effect and more pre-eclampsia (RR 1.85, high certainty) (Davidson 2021, PMID: 33870484).

Breastfeeding: the vitamin D question is the baby’s

Breast milk carries little vitamin D at ordinary maternal intakes, so the standard answer is 400 IU drops for the infant rather than a higher dose for you; the 6,400 IU maternal alternative worked in one trial but sits above the 4,000 IU adult limit and is a conversation with your pediatrician (the vitamin D guide has the trial). Your own numbers shift in two places: the iron RDA falls to 9 mg while you are not menstruating and the choline AI rises to 550 mg (NIH ODS iron; NIH ODS choline). Keep the DHA. Creatine and collagen have no controlled trial in breastfeeding women.

Perimenopause: the symptom claims run ahead of the trials

For hot flashes, the Cochrane review of black cohosh pooled 16 trials in 2,027 women and found no difference from placebo (Leach 2012, PMID: 22972105). The one creatine trial built for perimenopausal women, 36 participants across three creatine HCl arms and placebo, found its effects (faster reaction time, higher brain creatine) in the 1,500 mg medium-dose arm, measured reaction time rather than symptoms, and its mood-swing result did not reach significance (p = 0.06) (Korovljev 2026, PMID: 40854087). Magnesium has no hot-flash trial we would cite. Hormone therapy is the treatment with evidence, and a prescriber’s decision.

What the evidence does support here is less exciting. Periods often get heavier before they stop, so ferritin stays worth testing, and the calcium target steps up to 1,200 mg at 51. If you lift, creatine at 3–5 g of monohydrate a day is the same dose as at any age: strength rises within days, while lean mass barely moves, a non-significant 0.29 kg in the female subgroup of a 35-trial meta-analysis, against 1.46 kg in men (Delpino 2022, PMID: 35986981). Collagen belongs here for skin: 2.5 g a day of hydrolyzed peptides improved elasticity against placebo in 69 women aged 35 to 55 over 8 weeks (Proksch 2014, PMID: 23949208), and a meta-analysis of 19 trials, 95% of them in women, put the course at about 90 days (de Miranda 2021, PMID: 33742704). The gains are instrument-measured, and many trials were manufacturer-run.

After menopause: count calcium in food, correct a low D, lift with creatine, drop the iron

Calcium is one of the few nutrients whose RDA rises with age: 1,200 mg a day for women from 51, food and supplements together. Most of that is on your plate already, so the calcium for seniors guide counts food first and supplements only the gap, usually 200–500 mg, in doses of 500 mg or less with a meal, as citrate if you are over 65 or on an acid reducer. The trials explain the restraint. The Women’s Health Initiative gave 36,282 postmenopausal women 1,000 mg of calcium with 400 IU of D for seven years: hip fractures fell but not significantly (hazard ratio 0.88) and kidney stones rose 17% (Jackson 2006, PMID: 16481635); across 26 supplement trials the only trial with a clear fracture reduction was in frail elderly women low in both calcium and vitamin D (Bolland 2015, PMID: 26420387). The US Preventive Services Task Force recommends against 400 IU or less of vitamin D with 1,000 mg or less of calcium for primary fracture prevention in community-dwelling postmenopausal women (Grossman 2018, PMID: 29677309). Correct a low vitamin D; do not expect a pill to replace a bone-density scan.

Creatine after menopause is the best-tested pairing here and the most oversold. Two years of it with resistance training in 237 postmenopausal women left bone density unchanged but preserved femoral-neck geometry (Chilibeck 2023, PMID: 37144634); two years of 3 g a day in 200 women with no exercise program changed nothing (Sales 2020, PMID: 31257405). Pooled, 5 g or more with training added 0.37 kg of lean mass and 7.5 kg on the leg press (Naddafha 2026, PMID: 42141930). Collagen has one 12-month trial here, 5 g a day raising T-scores in 131 postmenopausal women with low bone density (König 2018, PMID: 29337906): a reason to try it, not a body of evidence.

Iron reverses: the RDA drops to the male 8 mg, and a multivitamin with iron taken for years risks overload, which the multivitamin for women guide calls the most common women’s-multi mistake. Magnesium keeps the 320 mg RDA it has had since 31, per the magnesium for seniors guide. The over-50 stack handles B12 and CoQ10.

When a women’s multivitamin is the sensible default, and when it is not

A women’s multi differs from any other in two ingredients, iron and folate, and those two decide it. It is the sensible default for a woman who could become pregnant and does not want to manage folic acid and iron separately, for a restricted diet, and as a prenatal; it is the wrong default after menopause, when the right product is iron-free. For a woman eating a varied diet with no gap to fill, the USPSTF found the evidence insufficient to say any multivitamin prevents cardiovascular disease or cancer (Mangione 2022, PMID: 35727271); the one large positive result is in a different age group, where COSMOS-Mind found better cognition in 2,262 adults with a mean age of 73 (Baker 2023, PMID: 36102337), about two years less cognitive aging (Vyas 2024, PMID: 38244989). The picks follow the multivitamin for women guide: NATURELO One Daily Multivitamin for Women $0.40/day with iron and folate before menopause, and the iron-free Thorne Basic Nutrients 2/Day $1.20/day after it.

The hopeful tier: what the women’s aisle sells without a trial behind it

Hair, skin and nails blends. The active claim is biotin, and the systematic review of biotin for hair found 18 published cases, every one in a person with an underlying cause of hair or nail loss, and no trial in healthy people (Patel 2017, PMID: 28879195). Collagen has no trial with hair as a primary outcome; its evidence is for skin, at 2.5 g, which the blends rarely carry (the hair, skin and nails stack).

“Hormone balance” blends. Vitex, DIM, maca, inositol and adaptogens sold together for cycles, mood and “estrogen dominance”. We could not find a randomized trial of any such blend, and the individual herbs’ small trials do not transfer to a blend at a fraction of the dose. A changed cycle or heavy bleeding needs a clinician and bloodwork.

“Women’s creatine” and gummies. On the 1,200 creatine labels in our census, monohydrate, the form every trial in women used, sits at a median 5 g per serving; creatine HCl, sold as gentler and “micro-dosed”, sits at 2 g. A smaller number, not a better one.

“Women’s probiotics.” Of 77 women-marketed labels, 14.3% name GR-1 or RC-14, the strains with the vaginal trials, and 93.5% hide their strain amounts inside a proprietary blend. For recurrent UTI the probiotic evidence is null (risk ratio 0.82, not significant) (Schwenger 2015, PMID: 26695595); cranberry probably helps (risk ratio 0.74) (Williams 2023, PMID: 37947276), at a dose a combined capsule does not carry.

Menopause blends and “menopause skin” capsules. Black cohosh is the best-tested ingredient and it failed its Cochrane review (Leach 2012, above). Collagen capsules run into arithmetic: of the 144 capsule labels in our format census, 70.8% direct less than the 2.5 g skin dose at the label’s maximum.

Magnesium for sleep and PMS. The sleep evidence is three trials in 151 older adults, sleep onset 17 minutes faster, at low to very low quality (Mah 2021, PMID: 33865376); PMS was rated insufficient in the 2025 review above; anxiety is suggestive in vulnerable groups and poor in quality (Boyle 2017, PMID: 28445426). It stays in the table because it is cheap and safe with normal kidneys.

What to test first: ferritin, 25(OH)D, and B12 if you are vegetarian or on metformin

Ferritin decides iron: below 30 ng/mL stores are low, and the fatigue trial above treated women under 50 µg/L; the ferritin test guide explains why it reads falsely normal when you are inflamed. 25-hydroxyvitamin D decides vitamin D: below 20 ng/mL is deficient, and in NHANES the share of women below 50 nmol/L is highest at 18–30 (31%) and lowest at 65 and over (7.8%), the reverse of the intuition; the 25(OH)D test guide covers reading the result. B12 decides a supplement most women do not think about: metformin lowered B12 by 19% over 4.3 years in a randomized trial, a number needed to harm of about 14 for outright deficiency (de Jager 2010, PMID: 20488910); among vegetarians, reviewed studies reported deficiency in 62% of pregnant women (Pawlak 2013, PMID: 23356638); and after 50, stomach acid declines. The MMA test guide and the B12 for vegetarians guide take it from there.

What it costs: $0.28/day for the core, $2.52/day for everything the aisle sells

A day of our catalog pick for each ingredient, at the studied dose. The core three for a menstruating woman (iron if low, folate, vitamin D) come to $0.28/day, about $8 a month. The pregnancy additions (choline, one softgel of DHA, vitamin D) are $0.44/day on top of a prenatal. The after-menopause core (a 500 mg calcium gap, vitamin D, creatine) is $0.50/day. All eleven cost $2.52/day, about $76 a month, most of it on ingredients whose evidence applies to a stage you are not in.

Cost per day in US dollars of our pick for each ingredient, at the studied dose
0 0.4 0.8 1.1 1.5 Iron (bisglycinate) $0.10 Folic acid / folate $0.13 Vitamin D3 $0.05 Choline $0.07 Calcium (citrate) + D $0.18 Creatine monohydrate $0.27 Omega-3 (DHA) $0.32 Probiotic, by strain $0.59 Collagen peptides $0.18 Magnesium glycinate $0.23 Multivitamin $0.40
The three with strong evidence (teal) total $0.28/day. The stage-specific four (amber) and the four with weaker or narrower evidence (grey) bring everything to $2.52/day. Source: Verified Supplement Data catalog, prices reviewed 2026-09-17; servings per day set by the cited trial or guideline dose.
Cost per day in US dollars of our pick for each ingredient, at the studied dose
ItemValue
Iron (bisglycinate)$0.10
Folic acid / folate$0.13
Vitamin D3$0.05
Choline$0.07
Calcium (citrate) + D$0.18
Creatine monohydrate$0.27
Omega-3 (DHA)$0.32
Probiotic, by strain$0.59
Collagen peptides$0.18
Magnesium glycinate$0.23
Multivitamin$0.40

Method: catalog price divided by servings per container, multiplied by the servings needed to reach the studied dose (two tablets of the calcium pick for a 500 mg gap, one softgel of the omega-3 pick, 2.5 g of the collagen scoop; one serving for the rest). Where that dose is smaller than the one the product's own listing is priced at (the omega-3 pick is listed at two softgels, the collagen pick at a full scoop), the figure here is lower than the listing's cost per day by exactly that ratio. Picks are the products the linked guides already recommend. Label figures come from four NIH DSLD censuses run for those guides; only findings that held in both halves of each read are printed, with denominators on the linked pages. What it cannot tell you: whether a cheaper product would serve you as well, what any product costs at checkout today, or which of these you personally need.

The product links below go to Amazon and we may earn a commission if you buy. It never changes which products we pick or what we say about them. How we choose.

Before menopause, $0.28/day (about $8/month): NOW Foods Iron 36 mg Double Strength (Ferrochel) $0.10/day if ferritin is low, Jarrow Formulas Methyl Folate 400 mcg $0.13/day if you could conceive, and Nature Made Vitamin D3 2000 IU $0.05/day if you test low.

Pregnant, $0.44/day on top of your prenatal: Nutricost Choline Bitartrate 650mg $0.07/day, one softgel of Sports Research Triple Strength Omega-3 (1250mg) $0.32/day, and the same vitamin D.

After menopause, $0.50/day: two tablets of Solgar Calcium Citrate with Vitamin D3 $0.18/day for a 500 mg gap, the same vitamin D, and Optimum Nutrition Micronized Creatine Monohydrate (60 servings) $0.27/day at 5 g if you lift. The product that names GR-1 and RC-14, Jarrow Fem-Dophilus, currently shows no offer on Amazon and we will not substitute for a strain-specific claim; for an antibiotic course, Culturelle Daily Probiotic (10B CFU, 30ct) $0.59/day carries the tested strain.

Check vitamin D price →

Frequently asked questions

What supplements should a woman take every day?

It depends on her stage. Before menopause: folic acid at 400 to 800 mcg if she could become pregnant, iron only if ferritin tests low, and vitamin D at 1,000 to 2,000 IU if she tests low; that core costs $0.28/day from our picks. In pregnancy: a prenatal, choline, about 200 mg of DHA and a vitamin D top-up. After menopause: the calcium gap after counting food, vitamin D if low, creatine if she lifts, no iron unless tested.

Do women need a different multivitamin than men?

Only in two ingredients, iron and folate; the rest matches any multivitamin. After menopause the iron becomes a liability, so the right multi is iron-free. For a woman eating a varied diet, the USPSTF found insufficient evidence that any multivitamin prevents heart disease or cancer; the one large positive result, in the COSMOS trials, was in adults with a mean age of 73.

Should women take iron every day?

Not without a test. In CDC NHANES data 10.5% of women aged 31 to 50 have ferritin below 12 ng/mL against 0.3% of men the same age. Iron accumulates, and taking it with normal stores buys nothing but stomach upset. Test ferritin; if it is low, take a bisglycinate form every other day and retest in two to three months. After menopause the RDA drops to 8 mg and most women should stop.

What supplements should I take when trying to get pregnant?

Folic acid, 400 to 800 mcg a day from at least a month before conception, because the neural tube closes before most women know they are pregnant; a prenatal delivers it with iron. Add vitamin D if you test low, and choline and DHA once pregnant. Creatine and collagen have no human trial in pregnancy; take a probiotic only for a specific reason agreed with your clinician.

What supplements help with perimenopause and menopause symptoms?

For hot flashes, none has held up: the Cochrane review of black cohosh in 2,027 women found no difference from placebo, and the one creatine trial in perimenopausal women measured reaction time, not symptoms. What the evidence supports here is unglamorous: keep testing ferritin while periods continue, count calcium in food against the 1,200 mg target from 51, correct a low vitamin D, and lift weights with 5 g of creatine.

Is creatine good for women?

Yes, at the same 3 to 5 g of monohydrate a day as men. In women who lift, strength rises within days; lean mass barely moves (a non-significant 0.29 kg in the female subgroup of a 35-trial meta-analysis). After menopause, two years with resistance training preserved bone geometry but not density, and 3 g a day without training did nothing. On the labels we read, creatine HCl sits at a median 2 g per serving against 5 g for monohydrate.

What blood tests should I get before buying supplements?

Three cover most of the women’s aisle: ferritin, because it decides whether iron helps or harms; 25-hydroxyvitamin D, because every vitamin D trial that failed gave it to people who already had enough; and B12 if you are vegetarian or vegan, take metformin, or are over 50. Nothing else on this page has a test that changes the decision.

Related guides

Sources

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