Restless Legs Syndrome: The Research

Restless Legs Syndrome (RLS) is a common neurological condition that causes an uncontrollable urge to move the legs, usually accompanied by uncomfortable sensations such as tingling, crawling, pulling, aching or burning. Symptoms typically occur during rest, particularly when sitting or lying down, and become worse in the evening and overnight, often improving temporarily with movement.

Because symptoms are most pronounced at night, RLS frequently disrupts sleep. Many people describe difficulty falling asleep, repeated night-time waking, or feeling unable to keep their legs still when trying to rest. Over time, this can lead to poor sleep quality, daytime fatigue, reduced concentration, irritability and low mood. Research has consistently shown that RLS is not simply a sleep complaint, but a condition with wider effects on physical and mental wellbeing.

Large population studies estimate that RLS affects 5–10% of adults, with 2–3% experiencing symptoms severe enough to interfere with daily life. A major review in The Lancet Neurology noted that RLS is “one of the most common neurological movement disorders worldwide” and confirmed its higher prevalence in women and increasing frequency with age. Individuals with moderate to severe RLS are also more likely to experience chronic insomnia, anxiety, depression and cardiovascular health issues, largely due to prolonged sleep disruption.

Despite its prevalence, RLS remains under-recognised and under-diagnosed. Researchers at Johns Hopkins Hospital have reported that many patients experience symptoms for years or even decades before receiving a diagnosis, with symptoms often misattributed to stress, anxiety or musculoskeletal problems. As Allen and Earley observed in Sleep Medicine, “diagnostic delay remains a significant issue in restless legs syndrome, contributing to prolonged patient suffering.”

Iron Deficiency and Why It Matters in RLS

Over the past decade, research from leading universities and hospitals has demonstrated a strong and consistent link between RLS and iron deficiency. Importantly, this relationship extends beyond iron levels in the blood to iron availability within the brain.

Iron is essential for normal brain function. Studies from institutions such as the Mayo Clinic and Harvard Medical School show that a substantial proportion of people with RLS have low or borderline iron stores, even when they are not anaemic. When iron status is assessed using thresholds relevant to neurological function rather than red blood cell production alone, up to 60% of people with RLS show evidence of iron deficiency.

This helps explain a common patient experience: being told blood tests are “normal” while symptoms persist. As Connor and colleagues wrote in the Journal of Neurology, “brain iron deficiency can be present despite normal peripheral iron measures.” The brain has higher and different iron requirements than the rest of the body, and standard blood tests do not always reflect what is happening within the nervous system.

People at Higher Risk of Iron Deficiency in RLS

• Women with heavy or prolonged menstrual bleeding
• People who have been pregnant
• Those with digestive conditions that impair iron absorption
• People with chronic inflammation or long-term illness
• Endurance athletes or very active individuals
• People following vegetarian or vegan diets, as plant-based iron is less easily absorbed by the body than iron from animal sources, meaning iron stores can gradually fall even when the diet appears balanced

Iron, Dopamine and the Brain

Iron plays a vital role in the brain beyond oxygen transport. It is required for:

• ✓Dopamine production and regulation
• ✓Energy production within brain cells
• ✓Healthy nerve signalling and insulation (myelin)

RLS is closely linked to changes in the dopamine system, particularly within the basal ganglia, a group of brain structures involved in movement and sensory processing.

Iron is required for tyrosine hydroxylase, a key enzyme involved in dopamine production. When iron levels in the brain are reduced, dopamine signalling becomes disrupted. As Allen and Earley explained, “iron deficiency alters dopaminergic function in a way that directly contributes to restless legs symptoms.”

Dopamine activity follows a circadian rhythm, declining in the evening and overnight. Research published in Movement Disorders demonstrated that this physiological drop in dopamine closely mirrors the timing of peak RLS symptoms, reinforcing that RLS has a biological rather than psychological basis.

Importantly, multiple studies confirm that brain iron levels do not consistently correlate with blood iron levels, which explains why RLS can occur even when routine tests appear reassuring.

What Brain Scans Have Shown

Advances in brain imaging over the last six years have significantly improved understanding of RLS. Modern MRI techniques, including quantitative susceptibility mapping, allow researchers to estimate iron levels within specific brain regions.

Studies from centres such as the University of Pennsylvania and Charité Berlin consistently demonstrate reduced iron levels in brain regions involved in movement and sensation, particularly the substantia nigra, a key dopamine-producing area. Moon and colleagues reported in Sleep that individuals with RLS show “significantly lower brain iron concentrations compared with matched controls, independent of peripheral iron status.”

These findings have led researchers to conclude that low brain iron is a core feature of RLS, rather than a secondary or coincidental finding.

Ferritin Levels: Why “Normal” May Not Be Enough

Ferritin is a blood marker used to estimate iron stores. Traditionally, ferritin thresholds have been designed to prevent anaemia, not to optimise brain function. However, research now shows that the brain requires higher iron stores than those needed to maintain normal haemoglobin.

A state of the art review in The Lancet Neurology reported that RLS severity and prevalence increase when ferritin levels fall below approximately 75 μg/L, even when haemoglobin remains normal. The authors noted that “iron deficiency relevant to restless legs syndrome may exist within the low-normal ferritin range.”

More recent guideline updates from the International Restless Legs Syndrome Study Group suggest that symptoms may persist until ferritin levels approach 100 μg/L or higher, particularly in individuals with long-standing or more severe symptoms. For this reason, modern clinical guidance recommends interpreting ferritin levels in the context of symptoms and neurological health, rather than relying solely on laboratory reference ranges.

Treatment Outcomes: What Happens When Iron Is Corrected

Recognition of iron deficiency as a central contributor to RLS has changed treatment approaches. Research from the past six years shows that correcting iron deficiency can significantly improve symptoms in many people.

Oral iron supplements may be helpful in mild deficiency, but are often limited by poor absorption, gastrointestinal side effects and slow symptom improvement. In contrast, intravenous (IV) iron has demonstrated more consistent benefits in moderate to severe RLS.

In a Mayo Clinic review, Silber and colleagues reported that 60–80% of appropriately selected patients experienced meaningful symptom improvement following IV iron therapy, with improvements in sleep quality, nocturnal symptoms and daytime functioning. Benefits are often seen within 4–8 weeks and may last 6 months to 2 years, depending on ongoing iron losses and individual risk factors.

Summary

RLS is now recognised as a biologically driven neurological condition, not a psychological or behavioural problem. Research from leading universities and hospitals has clearly demonstrated that low iron levels within the brain play a central role in the development and persistence of symptoms.

Because brain iron deficiency can exist even when blood tests appear normal, RLS is frequently missed or under-treated. An approach that considers iron status in a neurological context, rather than focusing solely on anaemia, offers a meaningful opportunity to improve sleep, energy and quality of life for people living with RLS.

Key Research Cited

1. Trenkwalder C et al. Lancet Neurology. 2016; 2023
2. Winkelman JW et al. Sleep. 2017; 2020
3. Allen RP, Earley CJ. Sleep Medicine. 2018
4. Silber MH et al. Mayo Clinic Proceedings. 2022
5. Garcia-Borreguero D et al. Lancet Neurology. 2021
6. Connor JR et al. Journal of Neurology. 2017; 2021
7. Chaudhuri KR et al. Movement Disorders. 2018; 2020
8. Moon HJ et al. Sleep. 2019
9. Schmidauer C et al. Movement Disorders. 2021
10. International Restless Legs Syndrome Study Group (IRLSSG). Consensus Guidelines, 2018–2024