Evidence explainerIron (ferrous sulfate vs bisglycinate vs other forms)
Iron After 50: Why Most Men and Postmenopausal Women Shouldn’t Take It Without a Blood Test
Tired? Iron is one of the first supplements people reach for. After menopause and for most men, needs drop to 8 mg a day, and extra iron has real downsides.
Key takeaways
- The iron RDA drops to 8 mg/day for men and for women 51 and older, versus 18 mg/day for women 19 to 50 [1].
- NIH advises checking iron status with a clinician before long-term supplementation, especially for men and postmenopausal women [1].
- People with hereditary hemochromatosis absorb too much iron and are advised to avoid iron and vitamin C supplements [1].
- Iron reduces absorption of levothyroxine and levodopa, two medicines common after 50 [1].
- The adult upper limit is 45 mg/day, based on gut side effects [1].
The evidence, graded
Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.
- Grade AImprovedStomach and bowel side effects with ferrous sulfateFerrous sulfate raised the odds of gastrointestinal side effects versus placebo (OR 2.32; 95% CI 1.74-3.08). Meta-regression found no clear link with the iron amount.
- Grade AImprovedHemoglobin and iron status in menstruating womenHemoglobin was 5.30 g/L higher with iron (high-quality evidence). Iron also lowered the risk of anaemia (RR 0.39; 3273 women) and iron deficiency (RR 0.62; 1088 women), moderate-quality evidence.
Your iron needs drop after menopause
Women aged 19 to 50 need 18 mg of iron a day, largely to replace menstrual losses; after 51 the RDA falls to 8 mg, the same as for adult men [1]. Many multivitamins aimed at younger women carry 18 mg, and standalone iron pills often carry far more.
The big iron trials were mostly in menstruating or pregnant women [2]. They show iron helps people who are low; they do not show it helps people who are not.
Why testing comes first
NIH notes that low iron has many causes and advises checking iron status with a clinician before long-term supplementation, especially for men and postmenopausal women, whose needs are low [1]. A test also tells your clinician whether low iron needs its cause looked into before anything is added.
The downsides of iron you don’t need
If a blood test does show low iron, your clinician will choose a form and schedule; the evidence on gentler schedules is in every-other-day iron. Feeling tired has many causes; B12 is another one worth testing after 50, see B12 in later life and on metformin [1].
- Gut side effects: ferrous sulfate roughly doubled the odds of stomach and bowel problems versus placebo [3].
- Hemochromatosis: people with this inherited condition absorb too much iron; liver specialists cited by NIH advise them to avoid iron and vitamin C supplements [1].
- Medicine interactions: iron lowers absorption of levothyroxine (some labels advise a 4-hour gap) and levodopa [1].
- Proton pump inhibitors can reduce iron absorption, so people on them may respond less to oral iron [1].
Keep reading
Full monographs
Related articles
- Iron Pills Without the Stomach Upset? The Case for Every-Other-Day Dosing
- Ashwagandha for Stress and Sleep: What the Trials Found, and Why the Results Vary So Much
- Ashwagandha Side Effects: The Liver, Thyroid and Pregnancy Warnings Behind Denmark’s Ban
- B12 After 50 and on Metformin: Why Levels Drop, and What the Trials Say About Fixing Them
Browse the full Supplement & Nutrient Encyclopedia or all supplement articles.
References
- [1]Iron: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025.
- [2]Daily iron supplementation for improving anaemia, iron status and health in menstruating women. Cochrane Database Syst Rev, 2016.
- [3]Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLoS One, 2015.