Restless leg syndrome (RLS) is triggered by a combination of brain chemistry, iron levels, lifestyle habits, medications, and underlying health conditions. About 7% of adults worldwide are affected, roughly 356 million people, with women nearly twice as likely to experience it as men. The triggers range from things you can control, like exercise timing and substance use, to biological factors that require medical attention.
Low Brain Iron and Dopamine Disruption
The most well-established biological trigger for RLS is iron deficiency in the brain, specifically in areas that produce and regulate dopamine. Dopamine is the chemical your brain uses to create smooth, purposeful movement. When iron levels drop in the brain’s movement-control centers, dopamine receptors stop functioning properly, and the result is the creeping, pulling, or throbbing sensations in your legs that define RLS.
Here’s what makes this tricky: your blood iron levels can look completely normal on a standard test while your brain is still iron-deficient. Researchers have found that people with RLS have significantly lower iron and ferritin levels in their cerebrospinal fluid compared to people without the condition, even when their blood work comes back fine. The dopamine receptor most affected is iron-dependent, meaning it literally cannot work correctly without adequate iron at the cellular level. For older adults, a serum ferritin level below 45 μg/L is increasingly used as a threshold for identifying iron deficiency linked to RLS, though brain iron status doesn’t always match what shows up in bloodwork.
Medications That Worsen Symptoms
Several common medication classes can trigger or intensify RLS. Antihistamines are among the most frequent culprits, particularly older, sedating types like diphenhydramine (the active ingredient in many over-the-counter sleep aids and allergy medications). Antidepressants, especially those that affect serotonin levels, are also well-documented triggers. Dopamine-blocking medications and lithium round out the list of known pharmaceutical triggers.
If you notice RLS symptoms appearing or worsening after starting a new medication, that connection is worth raising with whoever prescribed it. Switching to an alternative in the same class can sometimes resolve the problem.
Pregnancy
RLS is notably common during pregnancy, particularly in the third trimester, and the primary driver appears to be estrogen. Women who develop RLS during pregnancy have significantly higher estradiol levels compared to pregnant women without symptoms (around 34,200 pg/mL versus 25,500 pg/mL in one study). This hormonal spike likely interacts with the same dopamine pathways that iron deficiency disrupts.
The good news is that pregnancy-related RLS typically improves dramatically within the first two weeks after delivery and stays low through at least 12 weeks postpartum. Involuntary leg movements during sleep also drop significantly after birth. This pattern holds whether the RLS was new during pregnancy or a pre-existing condition that worsened.
Caffeine, Alcohol, and Smoking
Caffeine is widely cited as an RLS trigger, but the research is less clear-cut than most people assume. A large prospective study tracking men and women over time found no statistically significant association between caffeine consumption and RLS risk, even after controlling for other factors. That said, caffeine is a central nervous system stimulant with direct effects on muscle tissue, so individual sensitivity varies. If you notice a pattern between afternoon coffee and nighttime symptoms, cutting back is a reasonable experiment.
Alcohol shows a surprising trend in the opposite direction. Higher alcohol intake was associated with a modestly lower risk of RLS in both men and women, and previous research has linked alcohol abstinence with more restless legs. This doesn’t mean drinking is a treatment strategy, but it does suggest alcohol isn’t a trigger for most people.
Smoking tells a split story by sex. Women who smoked heavily (a pack or more per day) had a measurably higher risk of developing RLS, while no significant association was found in men. Nicotine stimulates dopamine release, which theoretically could help RLS, but the overall effect of heavy smoking in women points in the opposite direction.
Chronic Kidney Disease and Diabetes
Several chronic conditions can cause what’s called secondary RLS, meaning the restless legs are a downstream effect of another illness. Chronic kidney disease is one of the strongest associations. The buildup of waste products in the blood (uremia) that occurs when kidneys fail appears to directly trigger RLS, and symptoms tend to worsen the longer someone has been on dialysis. Iron deficiency, which is common in kidney disease patients, compounds the problem.
Diabetes is another common secondary cause, likely through its effects on peripheral nerves. Cardiovascular disease also shows up frequently alongside RLS, though the direction of that relationship is still being untangled.
Exercise Timing and Intensity
Regular moderate exercise generally helps RLS symptoms, but the details matter. Excessively long or intense workouts targeting the lower legs can make symptoms worse, as can yoga poses that place too much weight on a single leg. Sudden changes in your exercise routine also risk flaring symptoms.
Timing is just as important as intensity. Strenuous exercise within about two hours of bedtime can disrupt sleep, and since RLS symptoms peak during rest and inactivity in the evening, poor sleep and late-night exercise create a cycle that feeds on itself. Consistent, moderate activity earlier in the day is the pattern most likely to help rather than hurt.
Who Gets RLS and When
RLS prevalence rises steadily with age, starting around 5.5% in people in their early twenties and climbing to roughly 8.6% by the mid-sixties, where it plateaus. Women are affected at higher rates across every age group, with an overall prevalence of 8.3% compared to 6% in men. Women account for about 58% of all RLS cases globally.
The condition runs in families, particularly when it starts before age 40. People with a family history of RLS tend to develop symptoms earlier and may experience a more gradual worsening over decades, while those whose RLS is triggered by an identifiable cause like kidney disease or pregnancy often have a more sudden onset that tracks with the underlying condition.