Does iron affect sleep?

For one condition, yes. In people with restless legs syndrome, the urge to move the legs that keeps people awake at night, a 2019 Cochrane review found iron lowered the severity score by 3.78 points more than placebo (95% CI 1.31 to 6.25), across 7 trials with 345 people, on moderate certainty evidence. The same review found iron did not improve how well people said they slept. Outside restless legs, the trials of iron and sleep are few, small and mostly in children.

Established. Iron is a guideline treatment for restless legs syndrome when iron stores are low. The American Academy of Sleep Medicine (AASM) in 2025 strongly recommended intravenous ferric carboxymaltose for adults with restless legs and appropriate iron status, on moderate certainty evidence, and gave oral ferrous sulfate a conditional recommendation.

Drop in restless legs severity score against placebo, points

How far iron lowered the International Restless Legs Severity score (IRLS) beyond placebo, with 95 percent confidence intervals. The two ferric carboxymaltose reviews draw on largely the same trials, so they are not two independent confirmations. None of these bars measures sleep itself. Sources: cards ev-irs-01, ev-irs-04, ev-irs-05 and ev-irs-06 below.

What the trials found

Restless legs symptoms

Four meta-analyses agree that iron lowers restless legs scores. The Cochrane review covered 10 studies with 428 people, measured 2 to 12 weeks after treatment. A separate 2019 meta-analysis of 10 randomized trials found a drop of 3.55 points (95% CI 1.68 to 5.41) and a relative risk of improvement of 2.16. Two later reviews of intravenous ferric carboxymaltose, an iron drip given in clinic, found larger drops of 5.77 and 6.03 points, drawn from largely the same 7 trials. The 2025 one found no significant gain in restless legs quality of life.

Iron against placebo in restless legs, relative risk

Randomized trials, pooled

Relative risks with 95 percent confidence intervals. The cards we hold do not give how many people improved or had side effects in each arm, so these ratios cannot be turned into absolute numbers. The two reviews disagree on whether the excess of side effects is significant. Sources: cards ev-irs-03 and ev-irs-04 below.

The effect is largest when iron is clearly low. In 29 people with restless legs and iron deficiency anemia, one 1,500 mg infusion of ferric carboxymaltose lowered the score by 13.47 points at 6 weeks, against a rise of 1.36 on placebo, and sleep quality improved. That is one small trial in people who were anemic.

Unsettled. Relief of restless legs is not the same as better sleep, and the trials that measured sleep found little. In the Cochrane review, self-rated sleep quality was no different on iron than on placebo, a standardized difference of 0.19 (95% CI -0.18 to 0.56), in 3 trials with 128 people. The one study of sleep efficiency had 18 participants. Too few trials measured sleep to settle it either way.

Sleep outside restless legs

In 20 autistic children with insomnia and low normal ferritin, ferrous sulfate for 3 months raised iron stores but did not significantly shorten the time to fall asleep, -11.0 minutes against placebo (95% CI -28.4 to 6.4), measured with a wrist activity monitor. The trial enrolled fewer children than planned. In two placebo-controlled trials in 1,444 infants in Zanzibar and Nepal, where anemia was common, iron given for 12 months was consistently linked to longer night and total sleep. Sleep there came from mothers' reports as a secondary outcome, and the abstract gives no size of effect. Many of these infants were anemic, so the result may not apply to children who already have enough iron.

In 176 iron-deficient blood donors with ferritin of 30 ng/mL or less, sleep quality and restless legs symptoms improved after 8 to 12 weeks of oral or intravenous iron (p below 0.001), with no difference between the two. There was no placebo arm, so the improvement cannot be separated from expectation. A 2020 scoping review of 93 studies shows how thin this area is: iron deficiency was linked to restless legs in 22 of 42 association studies, and iron helped in 29 of 30 restless legs treatment studies, only 5 of them randomized. We found no randomized trial of iron on sleep quality in adults who are short of iron and do not have restless legs.

Who should be careful

Iron is not harmless to take blind. People with hereditary hemochromatosis absorb too much iron from food and are at risk of iron overload, according to the US National Institutes of Health Office of Dietary Supplements (NIH ODS). NIH ODS also notes that supplemental iron at 45 mg a day or more can cause nausea and constipation. 45 mg is the adult upper limit, and restless legs regimens such as 65 mg of elemental iron sit above it, which is why they are given under medical supervision.

In restless legs trials, the 2019 meta-analysis found side effects twice as likely on iron, a relative risk of 2.04 (95% CI 1.46 to 2.85), none of them severe, and the Cochrane review found a smaller excess that did not reach significance, 1.48 (95% CI 0.97 to 2.25). The intravenous form has its own issue. A 2021 meta-analysis of 42 trials of people treated for iron deficiency found low blood phosphate in 47 percent (95% CI 36 to 58) of those given ferric carboxymaltose, against 4 percent with another intravenous iron. Those figures come from trial arms in iron deficiency generally, not from restless legs trials.

Not for everyone. If you take levodopa, a drug used for Parkinson's disease and also for restless legs, NIH ODS warns that iron supplements can reduce how much of it you absorb. Observational data across 6 studies link low ferritin to augmentation, a worsening of restless legs caused by dopamine drugs, an association that does not show iron prevents it. If you have hemochromatosis, iron for sleep is not for you. For everyone else the AASM thresholds below depend on a blood test, so the test comes before the iron.

What expert bodies say

The AASM 2025 guideline advises iron for adults with restless legs when ferritin is 75 ng/mL or lower or transferrin saturation is under 20 percent, oral or intravenous. Between 75 and 100 ng/mL it advises intravenous iron only. In children the threshold is ferritin under 50 ng/mL. The guideline itself says these thresholds are consensus and have not been empirically tested. They are also higher than the cut-offs used to diagnose iron deficiency in general. No expert body in our cards recommends iron for sleep in people without restless legs.

How we searched

Searched: a local copy of PubMed for iron, ferritin, ferric carboxymaltose or ferrous with sleep, insomnia, restless legs or Willis-Ekbom disease, which returned 396 records, of which we scanned the top 60. Narrower searches returned 13 records on iron and sleep in infants and children, 21 on ferric carboxymaltose and low phosphate, and 4 on iron and restless legs from 2025. We also checked the NIH ODS iron fact sheet, which has no sleep content, the US trial registry, which had no trial of iron for restless legs, the open web, and the retraction database, which listed none of the included papers. Search run on 7 October 2026.

Included: the 2019 Cochrane review, three other meta-analyses of iron in restless legs, four randomized trials, a scoping review, a meta-analysis of observational studies on augmentation, a meta-analysis of low phosphate after intravenous iron, the AASM 2025 guideline and the NIH ODS fact sheet.

Excluded: biomarker and brain imaging studies that describe mechanism only, restless legs studies in kidney disease and dialysis already covered by the Cochrane review, a scoping review of guidelines with no effect sizes, and off-topic hits from the broad search.

What we read: the full text of the 2025 ferric carboxymaltose meta-analysis, abstracts for the other papers, and the NIH ODS page itself.

What we could not get: the full texts of the Cochrane review and of the AASM guideline, so their abstracts are what we used. A 2025 systematic review of 12 randomized trials in 511 patients turned up on the open web, was not in our corpus, and is not on this page.

What would change this answer

A placebo-controlled trial of iron on sleep quality in adults who are low in iron and do not have restless legs. This is the main gap, and it is the question most people are asking.
Restless legs trials that report sleep as a main outcome, not a side measure. Three trials with 128 people are too few to say whether easing the legs improves the night.
Trials that report how many people improved and had side effects in each arm, so the relative risks of 2.16 and 2.04 can be stated in absolute terms.
A test of the AASM ferritin thresholds, which the guideline says rest on consensus.

More on iron itself, including how much you need and where to get it: Iron guide.

The rest of the nutrient, in one place. Iron: why the number on the label is not the number your body gets → What it does, how much you need, who runs short, and what too much does, with the evidence level shown on every line.

The full guide

Iron: why the number on the label is not the number your body gets

The same question for other foods (sleep)

Sources

ev-irs-01 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of controlled trials · n = 345
Combining data from the seven trials using the IRLS to compare iron and placebo, use of iron resulted in greater improvement in IRLS scores (MD -3.78, 95% CI -6.25 to -1.31; I2= 66%, 7 studies, 345 participants) measured 2 to 12 weeks after treatment.
Who: adults diagnosed with restless legs syndrome, measured 2 to 12 weeks after treatment
Effect: IRLS MD -3.78 (95% CI -6.25 to -1.31); 7 trials, 345 participants; I2 66%; moderate-certainty evidence
Certainty: Best synthesis. 10 studies, 428 people overall; search to September 2017. Oral vs IV and low ferritin inclusion showed no significant subgroup differences; more benefit in dialysis trials.
Cochrane Database Syst Rev, 2019 · checked 2026-10-07 · we read the abstract
ev-irs-02 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of controlled trials · n = 128
Subjective sleep quality was no different between iron and placebo groups (SMD 0.19, 95% CI -0.18 to 0.56; I2 = 9%, 3 studies, 128 participants), nor was objective sleep quality, as measured by change in sleep efficiency in a single study (-35.5 +/- 92.0 versus -41.4 +/- 98.2, 18 participants).
Who: adults with restless legs syndrome
Effect: subjective sleep quality SMD 0.19 (95% CI -0.18 to 0.56); 3 studies; GRADE low to very low for secondary outcomes
Certainty: Key nuance for 'does iron help sleep': symptom relief is shown, sleep quality itself is not, with few trials measuring it.
Cochrane Database Syst Rev, 2019 · checked 2026-10-07 · we read the abstract
ev-irs-03 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of controlled trials · n = 298
Iron did not result in significantly more adverse events than placebo (RR 1.48, 95% CI 0.97 to 2.25; I2=45%, 6 studies, 298 participants).
Who: adults with restless legs syndrome
Effect: adverse events RR 1.48 (95% CI 0.97 to 2.25); 6 studies; I2 45%
Certainty: Point estimate leans toward more adverse events; trials short. See ev-irs-04 for a pooled RR that reached significance.
Cochrane Database Syst Rev, 2019 · checked 2026-10-07 · we read the abstract
ev-irs-04 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 10 RCTs
Iron therapy was associated with a significant decrease of the IRLSS of -3.55 [95% CI (-5.41) - (-1.68)] points and an increase in the percentage of patients with improvement of the IRLSS score, RR of 2.16 [95% CI 1.56-2.98].
Who: patients with restless legs syndrome in randomized trials of iron vs no iron
Effect: IRLSS -3.55 (95% CI -5.41 to -1.68); improvement RR 2.16 (95% CI 1.56 to 2.98); adverse events RR 2.04 (95% CI 1.46 to 2.85), not severe
Certainty: Consistent with Cochrane on efficacy; differs on adverse events (significant here). Adverse events did not raise discontinuation.
Eur J Intern Med, 2019 · checked 2026-10-07 · we read the abstract
ev-irs-05 · Meta-analysis or systematic review · systematic review and meta-analysis of studies of intravenous ferric carboxymaltose · n = 539
FCM significantly reduced IRLS scores (WMD = -5.77; 95% CI = [-8.85, -2.70]; p = 0.0002) and improved VAS and SF-36 scores compared to placebo.
Who: patients diagnosed with restless legs syndrome
Effect: IRLS WMD -5.77 (95% CI -8.85 to -2.70); RLS quality of life not significantly improved; more adverse events, mainly nausea, no difference in severe events
Certainty: IV iron, a clinic treatment, not a dietary supplement. Overlaps with ev-irs-06 (same trials).
Front Neurol, 2024 · checked 2026-10-07 · we read the abstract
ev-irs-06 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 537
All 7 studies reported international RLS severity scale (IRLS) and the pooled analysis revealed a significant reduction in IRLS score favoring IV FCM [WMD: -6.03, 95 % CI (-10.11, -1.96), p = 0.004].
Who: patients with restless legs syndrome
Effect: IRLS WMD -6.03 (95% CI -10.11 to -1.96), p = 0.004; SF-36 WMD 7.44 (95% CI 1.67 to 13.20)
Certainty: Same evidence base as ev-irs-05; searched PubMed, Google Scholar, Medline only.
Sleep Med, 2024 · checked 2026-10-07 · we read the abstract
ev-irs-07 · Randomized controlled trial(s) · randomized double-blind placebo-controlled trial · n = 29
At week six post-infusion, FCM compared to placebo group showed significant improvement from baseline in IRLS score (-13.47 ± 7.38 vs. 1.36 ± 3.59).
Who: restless legs syndrome patients with iron deficiency anemia
Effect: IRLS change at week 6: -13.47 +/- 7.38 (FCM) vs 1.36 +/- 3.59 (placebo); sleep quality improved; no serious adverse events
Certainty: Small; the effect is largest when iron deficiency is clear.
Sleep Med, 2021 · checked 2026-10-07 · we read the abstract
ev-irs-08 · Randomized controlled trial(s) · randomized placebo-controlled trial, ferrous sulfate 3 mg/kg/day for 3 months · n = 20
Iron supplementation improved iron status (+18.4 ng/mL active versus -1.6 ng/mL placebo, P = 0.044) but did not significantly improve the primary outcome measures of sleep onset latency (-11.0 minutes versus placebo, 95% confidence interval -28.4 to 6.4 minutes, P = 0.22) and wake time after sleep onset (-7.7 minutes versus placebo, 95% confidence interval -22.1 to 6.6 min, P = 0.29) as measured by actigraphy.
Who: children with autism spectrum disorders, insomnia and low normal ferritin
Effect: sleep onset latency -11.0 min vs placebo (95% CI -28.4 to 6.4), P = 0.22; wake after sleep onset -7.7 min (95% CI -22.1 to 6.6)
Certainty: Underpowered (low enrollment); clinician global sleep score improved (P = 0.047).
Pediatr Neurol, 2020 · checked 2026-10-07 · we read the abstract
ev-irs-09 · Randomized controlled trial(s) · two randomized placebo-controlled trials of iron-folic acid with or without zinc, 12 months · n = 1444
Supplemental iron was consistently associated with longer night and total sleep duration.
Who: infants in Pemba Island, Zanzibar (n=877) and Nepal (n=567), many anemic
Effect: supplemental iron consistently associated with longer night and total sleep duration (maternal report); effect size not given in the abstract
Certainty: Sleep by maternal report, secondary outcome; populations with high anemia, so results may not apply to iron-replete children.
J Dev Behav Pediatr, 2009 · checked 2026-10-07 · we read the abstract
ev-irs-10 · Observational data · randomized controlled trial (IV vs oral iron, no placebo), pre-planned secondary analysis · n = 176
We found a significant improvement in the severity of symptoms for RLS, fatigue and sleep quality (p < 0.001).
Who: whole-blood and platelet donors aged 18-65 with ferritin <=30 ng/mL
Effect: significant improvement in RLS, fatigue and sleep quality severity (p < 0.001); IV vs oral no difference
Certainty: No placebo arm: before-after comparison for sleep, so placebo effect cannot be excluded.
Nutrients, 2020 · checked 2026-10-07 · we read the abstract
ev-irs-11 · Position of an expert body · clinical practice guideline, GRADE-based systematic review · n = —
Consensus guidelines, which have not been empirically tested, suggest that supplementation of iron in adults with RLS should be instituted with oral or IV iron if serum ferritin ≤ 75 ng/mL or transferrin saturation < 20%, and only with IV iron if serum ferritin is between 75 and 100 ng/mL.
Who: adults and children with restless legs syndrome
Effect: oral or IV iron if ferritin <=75 ng/mL or TSAT <20%; IV only if ferritin 75-100 ng/mL; children: ferritin <50 ng/mL
Certainty: Thresholds are higher than for general iron deficiency and, per the guideline, consensus-based and not empirically tested.
J Clin Sleep Med, 2025 · checked 2026-10-07 · we read the abstract
ev-irs-12 · Position of an expert body · clinical practice guideline, GRADE-based systematic review · n = —
In adults with RLS, the AASM recommends the use of IV ferric carboxymaltose over no IV ferric carboxymaltose in patients with appropriate iron status (see good practice statement for iron parameters) (strong recommendation, moderate certainty of evidence).
Who: adults with restless legs syndrome and appropriate iron status
Effect: IV ferric carboxymaltose: strong recommendation, moderate certainty; ferrous sulfate: conditional, moderate certainty
Certainty: Iron sits alongside gabapentinoids as a first-line option; dopamine agonists now suggested against for standard use.
J Clin Sleep Med, 2025 · checked 2026-10-07 · we read the abstract
ev-irs-13 · Observational data · scoping review of mixed study designs · n = 93 studies
A statistically supported positive association with ID was found in 22/42 RLS, 3/8 PLMs, 1/2 SDB, 3/4 GSD, and 1/2 ADHD-SDs association studies.
Who: studies of iron deficiency and sleep disorders, 1972-2019
Effect: positive association with ID in 22/42 RLS studies, 3/4 general sleep disturbance studies; iron beneficial in 29/30 RLS treatment studies (5 RCTs)
Certainty: Vote counting, mixed designs; shows how little exists on iron and sleep outside RLS.
Sleep Med Rev, 2020 · checked 2026-10-07 · we read the abstract
ev-irs-14 · Observational data · systematic review and meta-analysis of observational studies · n = 907
The results revealed that augmented RLS was significantly associated with low serum ferritin levels (p = 0.002), high LEDs (p = 0.026), and nonsignificantly associated with high IRLS scores (p = 0.227).
Who: RLS patients with (n=220) and without (n=687) augmentation
Effect: augmented RLS significantly associated with low serum ferritin (p = 0.002)
Certainty: Observational; association only.
Sleep Med, 2023 · checked 2026-10-07 · we read the abstract
ev-irs-15 · Observational data · systematic review and meta-analysis of prospective clinical trials (single-arm and comparative) · n = 42 trials
Across the 42 clinical trials included in the meta-analysis, FCM induced a significantly higher incidence of hypophosphataemia than IIM (47%, 95% CI 36-58% vs. 4%, 95% CI 2-5%), and significantly greater mean decreases in serum phosphate (0.40 vs. 0.06 mmol/L).
Who: patients treated for iron deficiency with IV ferric carboxymaltose or iron isomaltoside
Effect: hypophosphatemia incidence FCM 47% (95% CI 36-58%) vs IIM 4% (95% CI 2-5%)
Certainty: Relevant because FCM is the AASM's strongly recommended RLS iron. Pooled incidences from trial arms, not randomized comparisons.
Br J Clin Pharmacol, 2021 · checked 2026-10-07 · we read the abstract
ev-irs-16 · Position of an expert body · government fact sheet · n = —
High doses of supplemental iron (45 mg/day or more) may cause gastrointestinal side effects, such as nausea and constipation [5].
Who: adults taking iron supplements
Effect: gastrointestinal side effects at 45 mg/day or more of supplemental iron
Certainty: 45 mg/day is the adult UL; RLS regimens (e.g. 65 mg elemental iron) sit above it and need medical supervision.
NIH Office of Dietary Supplements, Iron Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
ev-irs-17 · Position of an expert body · government fact sheet · n = —
Some evidence indicates that in healthy people, iron supplements reduce the absorption of levodopa (found in Sinemet and Stalevo), used to treat Parkinson’s disease and restless leg syndrome, possibly through chelation [101-103].
Who: people taking levodopa
Effect: iron supplements may reduce levodopa absorption, possibly through chelation
Certainty: Direct interaction for RLS patients treated with levodopa.
NIH Office of Dietary Supplements, Iron Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
ev-irs-18 · Position of an expert body · government fact sheet · n = —
Individuals with hereditary hemochromatosis, which predisposes them to absorb excessive amounts of dietary iron, have an increased risk of iron overload [39].
Who: individuals with hereditary hemochromatosis
Effect: increased risk of iron overload
Certainty: Why iron for sleep should follow a ferritin test, not be taken blind.
NIH Office of Dietary Supplements, Iron Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section

How this page was made. Evidence was extracted from primary sources into cards, every number was re-checked against the source, and the text was written from those cards. Bioma Learn has no human medical reviewer at this time, and we say so rather than invent one. Methodology. This is information, not medical advice.