Restless leg syndrome (RLS) develops from a combination of genetic predisposition, brain chemistry imbalances, and environmental triggers. About 5 to 10 percent of adults in the United States experience it, and for most people, no single cause explains the condition on its own. Instead, several factors layer on top of each other to produce that irresistible urge to move your legs, especially at night.
The Role of Dopamine and Iron in the Brain
The most well-understood biological driver of RLS is a disruption in how the brain uses dopamine, a chemical messenger involved in movement control. Research points to a subtle dysfunction in dopamine receptors within the basal ganglia, the brain region that coordinates smooth, voluntary movement. People with RLS appear to have higher-than-normal availability of certain dopamine receptors, which paradoxically signals that the system isn’t working efficiently.
Iron plays a critical role because your brain needs it to produce and regulate dopamine. Even when blood iron levels appear normal on standard tests, iron stores in the brain itself can be low enough to throw dopamine signaling off balance. The International Restless Legs Syndrome Study Group recommends checking serum ferritin (a measure of stored iron) and considering iron supplementation when levels fall below 75 mcg/L. This threshold is notably higher than what most labs flag as “low,” which means your iron could be technically normal but still contributing to symptoms.
Genetics and Family History
RLS runs strongly in families. Twin studies estimate that genetics account for 54 to 69 percent of a person’s risk of developing the condition, making heredity the single largest contributing factor. If one of your parents has RLS, your chances of developing it are significantly higher than the general population.
Researchers have identified more than 20 genetic regions linked to RLS. The strongest association is with a gene called MEIS1, which is involved in early nervous system development. A specific variant in this gene reduces the activity of a regulatory region in brain structures that form during fetal development. Other identified genes, including BTBD9 and SKOR1, also play roles in nervous system signaling. Each individual variant adds only a small amount of risk on its own, but together they can meaningfully shift the odds.
Who Gets RLS Most Often
RLS affects women more often than men, for reasons that aren’t fully understood. Prevalence also increases with age, though symptoms can begin at any point in life. Children develop RLS too, at a rate of roughly 2 to 4 percent, though it’s frequently misdiagnosed as “growing pains” or hyperactivity.
Pregnancy is a notable trigger. About 21 percent of pregnant women develop RLS across all trimesters, with symptoms peaking in the third trimester at roughly 23 percent. The combination of increased iron demands, hormonal shifts, and circulatory changes likely explains this spike. For most women, symptoms resolve within weeks of delivery.
Medical Conditions That Trigger RLS
Several health conditions make RLS significantly more likely. When the syndrome arises from an identifiable underlying cause, it’s called secondary RLS.
- Kidney disease: Among patients with end-stage renal disease, about 27 percent develop RLS. The kidneys help regulate iron metabolism and clear waste products from the blood, and their failure disrupts both processes in ways that affect dopamine function.
- Peripheral neuropathy: Nerve damage, particularly from diabetes, is closely linked to RLS. Certain types of neuropathy involving the small sensory fibers in the skin appear especially likely to trigger symptoms. The damaged nerves send abnormal signals to the spinal cord, which may activate the same pathways involved in RLS. Diabetic neuropathy, amyloid neuropathy, and inherited nerve disorders are all prone to producing RLS, sometimes as one of the earliest noticeable symptoms.
- Iron deficiency: Even without full-blown anemia, low iron stores act as one of the most common environmental triggers. This is true whether the deficiency comes from diet, heavy menstrual periods, frequent blood donation, or digestive conditions that impair absorption.
Medications That Can Cause or Worsen Symptoms
Certain common medications trigger or intensify RLS. Sedating antihistamines like diphenhydramine (the active ingredient in Benadryl and many over-the-counter sleep aids) are among the most frequent culprits. These drugs cross into the brain easily and interfere with dopamine activity. Non-sedating antihistamines, like loratadine or cetirizine, don’t penetrate the brain as readily and are much less likely to cause problems.
Antidepressants, particularly SSRIs and SNRIs, are another well-known trigger. These medications alter the balance of brain chemicals in ways that can unmask or amplify RLS in people who are already predisposed. If you notice your legs becoming restless after starting a new medication, that timing is worth paying attention to.
How RLS Is Identified
There’s no blood test or brain scan that confirms RLS. Diagnosis relies on five clinical criteria, all of which need to be present:
- You feel an urge to move your legs, usually accompanied by uncomfortable sensations like crawling, pulling, or aching.
- The urge begins or worsens when you’re resting or inactive, such as lying in bed or sitting for a long period.
- Moving your legs, walking, or stretching provides at least partial relief for as long as you keep moving.
- Symptoms are worse in the evening or at night than during the day.
- The symptoms aren’t better explained by another condition, such as arthritis, leg cramps, poor circulation, or habitual foot tapping.
That last criterion matters because many conditions mimic RLS. Leg cramps involve sudden muscle tightening rather than an urge to move. Poor circulation causes aching that doesn’t follow the evening-and-rest pattern. A careful evaluation helps separate RLS from these lookalikes, which is important because the treatments are different.
Why Symptoms Follow a Nightly Pattern
One of the most distinctive features of RLS is its circadian rhythm. Dopamine levels in the brain naturally fluctuate throughout the day, dipping in the evening and reaching their lowest point at night. For someone whose dopamine system is already compromised by genetics, low iron, or another trigger, this nightly dip pushes signaling below the threshold needed for comfortable stillness. That’s why the same person who walks around fine during the day can find it unbearable to sit through a movie or lie in bed at night.
Iron metabolism follows a similar daily cycle, with serum iron levels dropping in the evening. This double dip in both dopamine and iron creates a window of vulnerability that lines up precisely with when most people are trying to sleep.