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Iron, a common mineral (and, paradoxically, a common mineral deficiency in humans) is important to the brain and vital for normal brain development and human behavior. It is a key cofactor in the making of neurotransmitters, chemicals in the brain that affect neuron signaling, including serotonin, norepinephrine, and especially dopamine. Iron is also necessary for the enzyme monoamine oxidase to break down these neurotransmitters.
Imbalances in levels of the neurotransmitter dopamine can lead to muscle and behavioral problems. Depending on the location and direction (high or low) of the imbalance in the brain, dopamine problems can cause stiffness in muscles, tremor, irrepressible urges to move while at rest (also known as restless legs syndrome), problems with attention, concentration, motivation, and depression, but also psychosis, paranoia, and aggression. Restless legs syndrome is often successfully treated with iron supplementation, and the numbers of dopamine receptors in areas of the brain will change depending on the iron levels in the brain.
Attention Deficit Hyperactivity Disorder is a common condition occurring in 5-15% of children and up to 5% of adults worldwide. It’s often hereditary, and due to the typical symptoms of motor restlessness, poor concentration, and distractibility, it is thought at least in part to be caused by problems with dopamine levels or the efficiency of dopamine receptors in the brain. Medications that help symptoms of ADHD (such as stimulants) modulate the levels of dopamine and norepinephrine in the brain. Methylphenidate (trade name Ritalin), for example, is a dopamine reuptake inhibitor that keeps more dopamine in the synapse. In genetic studies, certain dopamine transporter genes and D4 receptor genes were both associated with clinical symptoms of ADHD.
Multiple studies have now shown that ADHD in children is associated with low levels of serum iron and ferritin (another measure of iron) compared to control children without ADHD. Iron supplementation has also been shown to improve symptoms of ADHD.
Low iron levels have different sequelae in children than in adults, particularly when it comes to behavior and development. Iron deficiency in young children can lead to permanently lower IQ, developmental delays, and behavioral disturbances, which can only be partially ameliorated with iron supplementation later on in childhood. Neural development begins before birth, of course, but dopamine neuron maturation and migration continues through puberty, with subsequent modification and “pruning” happening up until adulthood. Iron levels influence neuron development (shown in animal studies). It’s possible a higher prevalence of iron deficiency in children than adults along with the slow progress of dopamine neuron maturation and development could partly explain why children tend to have a higher incidence of ADHD than adults, and the symptoms in children tend to include more motor restlessness. Following this line of reasoning, early recognition of iron deficiency and iron supplementation in children may ameliorate or even prevent some types of ADHD by positively influencing dopamine neuron development.
There are limited studies of adults with ADHD and the correlations between iron deficiency and symptoms are not so clear. In addition, vitamin and mineral supplements have had mixed results as treatment. In these populations, however, the only common deficiency found was vitamin D.
More research needs to be done to fully understand the connection between iron, dopamine, and ADHD, but it would make sense for folks with ADHD symptoms, particularly children, to get serum ferritin levels measured, and to replete iron deficiency when discovered. Since iron excess can also cause health problems and children with their smaller body sizes are more vulnerable to the effects of vitamin and mineral overdoses, it wouldn’t be safe to aggressively supplement iron without checking levels first.
More information about dopamine can be found here.
More information about iron and the brain can be found here.
Copyright Emily Deans MD
