Restless Legs and Iron: Your Ferritin Can Be Normal and Still Too Low
normal and clinically useless. The International Restless Legs Syndrome Study Group’s task force reviewed
299 papers, of which 31 met inclusion criteria, and set two thresholds that sit far above where most
laboratories draw the line for normal. Oral iron, 65 mg of elemental iron, is possibly effective for
treating RLS in those with serum ferritin of 75 mcg/l or below. And
intravenous ferric carboxymaltose, 1000 mg, is effective for moderate to severe RLS in those with
serum ferritin under 300 mcg/l, and could be used as first-line treatment for RLS in adults. Read
those numbers against a typical lab reference range, which often starts at 15 or 30. A ferritin of 45 will
be reported as normal, will be dismissed in a two-minute appointment, and sits well inside the range where
this guideline says oral iron is worth trying. The mechanism is why: brain iron deficiency has been
implicated in the pathophysiology of RLS, and brain iron is not the same measurement as blood iron.
If you have restless legs and were told your iron is fine, this page is about the specific number that
was probably not checked against the right threshold.
The two numbers
From the IRLSSG task force report, the evidence-based and consensus clinical practice guidelines for the
iron treatment of restless legs syndrome:
| Treatment | Ferritin threshold | Strength |
|---|---|---|
| Oral iron, 65 mg elemental | 75 mcg/l or below | Possibly effective |
| IV ferric carboxymaltose, 1000 mg | Under 300 mcg/l | Effective for moderate to severe RLS; could be first-line |
Now put a typical laboratory reference range next to that. Many labs flag ferritin as low only below
15 or 30 mcg/l.
So a result of 45 comes back unflagged. It is normal by the lab’s definition and it is
inside the treatable range by the guideline’s. A result of 150 is comfortably normal by
any general standard and still under the threshold at which the guideline considers intravenous iron
effective for moderate to severe disease.
This is not a lab error. Reference ranges describe the population; treatment thresholds describe a
condition. RLS happens to be a condition where the two diverge enormously.
Why the threshold is so high
Because the deficiency that matters is not in your blood.
Brain iron deficiency has been implicated in the pathophysiology of RLS. Iron is required
for dopamine synthesis, and the relevant shortfall is in brain tissue rather than in circulating stores.
Serum ferritin is a proxy for the wrong compartment, and an imperfect one, which is why the threshold has to
be set well above the point at which the rest of the body starts complaining.
Put differently: by the time your ferritin is low enough to be flagged as anaemia-adjacent, your brain has
been short for a long time.
What the evidence base actually looks like
The task force searched MEDLINE from inception to July 2016, identified 299 papers, and
found 31 that met the inclusion criteria of human research on iron treatment of RLS or
periodic limb movements, with a sample size of at least five, published in English.
Of those, four studies in adults were given a Class I rating: one for IV iron sucrose,
and three for IV ferric carboxymaltose.
Notice the shape of that. The strongest evidence is for the intravenous route. Oral iron is
described as possibly effective, which is a weaker claim, and it is the route most people will
actually be offered.
For children the guideline is blunt: there is insufficient evidence to make conclusions
on the efficacy of oral or IV iron in children.
Get the number, then ask for the threshold
The action here is not to start iron. It is to find out what your ferritin
actually is, as a number rather than as the word normal, and then compare it against 75 rather than
against the lab’s low-end flag. If it is at or below 75 and you have RLS, the guideline supports a
conversation about 65 mg of elemental iron. If it is well below and you also have symptoms of anaemia, that
is a doctor’s appointment rather than a supplement decision, because unnecessary iron causes constipation and
stomach upset and is genuinely harmful in undiagnosed iron overload.
Ferritin test kits
Iron with vitamin C
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purchases. The test is first because the entire guideline is written around a threshold, and a threshold is
useless without a measurement.
If you do take oral iron, how you take it decides how much arrives
Non-heme iron, the kind in supplements and plants, is poorly absorbed and is actively blocked by ordinary
things people take it with.
Inhibitors documented in the iron absorption literature:
- Polyphenols, found in black and herbal tea, coffee, wine, legumes, cereals, fruit and
vegetables - Phytates, with a dose-dependent effect on iron absorption
- Calcium, which inhibits both heme and non-heme iron
- Oxalic acid, found in spinach, chard, beans and nuts
And the one thing that overcomes them:
Vitamin C can overcome the effects of all dietary inhibitors when it is included in a diet with
high non-heme iron availability.
Practically: iron with orange juice or a vitamin C tablet, and not with tea, coffee, milk or a calcium
supplement. Taking an iron tablet with your morning tea is close to the worst version of the routine, and it
is what a lot of people do.
For scale on how inefficient this is at baseline, heme iron, the form in meat, is described as the most
easily absorbable form at 15% to 35%, and contributes 10% or more of total absorbed iron.
Non-heme iron is less well absorbed than that.
What this page is not saying
Not everyone with restless legs is iron deficient, and iron is not a treatment for RLS in someone whose
ferritin is 400.
The guideline’s own structure makes this clear: it is a set of thresholds, not a blanket
recommendation. Above 300 there is no iron recommendation at all. Between 75 and 300 the recommendation is
intravenous and belongs in a clinic. At or below 75, oral iron enters the picture.
RLS also has non-iron causes and triggers worth ruling out with a doctor, including pregnancy, kidney
disease, and several common medications. And if your symptoms are severe, the relevant conversation is a
referral rather than a supplement, because the strongest evidence in this guideline is for a treatment that
is given by infusion.
Frequently Asked Questions
What ferritin level is too low for restless legs?
Far higher than most people are told. The IRLSSG guideline states that oral iron at 65 mg of elemental
iron is possibly effective for treating RLS in those with serum ferritin of 75 mcg/l or below, and that
intravenous ferric carboxymaltose at 1000 mg is effective for moderate to severe RLS in those with serum
ferritin under 300 mcg/l. Many laboratory reference ranges flag ferritin as low only below 15 or 30, so a
result inside the treatable range is routinely reported as normal.
My doctor said my iron was normal. What do I do?
Ask for the actual number rather than the word. Normal is defined by the laboratory’s population reference
range; the thresholds above are defined by a condition-specific guideline, and for restless legs the two
diverge by a wide margin. A ferritin of 45 or 60 is normal by the first standard and inside the range where
this guideline supports trying oral iron by the second. Bring the guideline’s numbers to the conversation
rather than the conclusion.
Why does the threshold need to be so high?
Because the deficiency is in the brain rather than in the blood. Brain iron deficiency has been implicated
in the pathophysiology of RLS, and serum ferritin is only an indirect proxy for brain iron stores. Iron is
needed for dopamine synthesis, and the shortfall that produces symptoms occurs at levels of circulating iron
that would not trouble anything else in the body. That is why the treatment threshold sits above the
deficiency threshold rather than at it.
Is oral iron or IV iron better?
The stronger evidence is for intravenous. Of the 31 studies that met the task force’s inclusion criteria,
four in adults received a Class I rating, one for IV iron sucrose and three for IV ferric carboxymaltose, and
the guideline states that ferric carboxymaltose at 1000 mg could be used as first-line treatment for RLS in
adults. Oral iron is described more cautiously as possibly effective. That is worth knowing because oral is
what most people will be offered first, and its weaker rating is not a reason to skip it, only a reason to
know what to do if it fails.
How should I take iron so it actually absorbs?
With vitamin C, and away from tea, coffee, milk and calcium. The absorption literature lists polyphenols
in black and herbal tea, coffee and wine, phytates with a dose-dependent effect, calcium which inhibits both
heme and non-heme iron, and oxalic acid in spinach, chard, beans and nuts as inhibitors. Vitamin C is
described as able to overcome the effects of all dietary inhibitors when included in a diet with high
non-heme iron availability. A tablet taken with morning tea is close to the least effective way to do it.
Does this apply to children with restless legs?
The guideline declines to say. It states that only Class IV studies have evaluated iron treatment in
children, and that there is insufficient evidence to make conclusions on the efficacy of oral iron or IV iron
in children. That is not a statement that iron does not help children; it is a statement that nobody has
produced the evidence. Paediatric RLS is a specialist conversation rather than one to resolve from a page
like this.
Can I just take iron without testing?
No, and this is the one nutrient on this site where we consistently say so. Iron taken without deficiency
causes constipation and stomach upset for no benefit, and is genuinely harmful in anyone with undiagnosed
iron overload such as haemochromatosis. The entire guideline is constructed around thresholds, which means it
is unusable without a measurement. Test, get the number, then decide.
What if my ferritin is above 300?
Then iron is not the answer to your restless legs, on this guideline. The recommendations stop there: the
IV threshold is under 300 and the oral threshold is 75 or below. Above 300 there is no iron recommendation at
all, and the useful next step is a conversation about the other causes and treatments for RLS rather than a
supplement. High ferritin can also reflect inflammation or liver disease rather than iron stores, which is
another reason to interpret it with a clinician.
Sources
- Allen RP, Picchietti DL, Auerbach M, Cho YW, Connor JR, Earley CJ, Garcia-Borreguero D, Kotagal S,
Manconi M, Ondo W, Ulfberg J, Winkelman JW; International Restless Legs Syndrome Study Group. Evidence-based
and consensus clinical practice guidelines for the iron treatment of restless legs syndrome/Willis-Ekbom
disease in adults and children: an IRLSSG task force report. Sleep Med. 2018;41:27-44. PMID 29425576. Brain
iron deficiency has been implicated in the pathophysiology of RLS. A literature search of MEDLINE from
inception to July 2016 identified 299 papers, of which 31 met the inclusion criteria of human research on the
treatment of RLS or periodic limb movements with iron, sample size of at least five, and publication in
English. Four studies in adults were given a Class I rating, one for IV iron sucrose and three for IV ferric
carboxymaltose; only Class IV studies have evaluated iron treatment in children. Ferric carboxymaltose
(1000 mg) is effective for treating moderate to severe RLS in those with serum ferritin <300 mcg/l and
could be used as first-line treatment for RLS in adults. Oral iron (65 mg elemental iron) is possibly
effective for treating RLS in those with serum ferritin ≤75 mcg/l. There is insufficient evidence to make
conclusions on the efficacy of oral iron or IV iron in children. Checked August 2026 —
PubMed 29425576 - Iron absorption, StatPearls. Heme iron is the most easily absorbable form (15% to 35%) and contributes
10% or more of total absorbed iron; non-heme iron is derived from plants and iron-fortified foods and is less
well absorbed. Inhibitors of non-heme iron absorption include phytates, with a dose-dependent effect on iron
absorption; polyphenols found in black and herbal tea, coffee, wine, legumes, cereals, fruit and vegetables;
calcium, which inhibits both heme and non-heme iron; and oxalic acid, found in spinach, chard, beans and
nuts. Vitamin C can overcome the effects of all dietary inhibitors when it is included in a diet with high
non-heme iron availability. Checked August 2026 —
StatPearls NBK448204
The thresholds on this page are quoted from the IRLSSG task force
report and were checked against it in August 2026. Laboratory reference ranges vary between laboratories, so
the comparison with a typical low-end flag of 15 or 30 mcg/l is a general observation rather than a statement
about your specific report; check what your own laboratory used. This page summarises a published guideline,
cannot see your results, and is not a diagnosis.
