Iron deficiency negatively affects behavioral measures of learning, indirect neural measures of dopamine, and neural efficiency.

Iron deficiency (ID) is the most prevalent nutrient deficiency in the world, with a growing literature documenting the negative effects of ID on perception, attention, and memory. Animal models of ID suggest that dysregulation of dopamine is responsible for the deficits in memory. However, evidence that ID affects dopamine in humans is extremely limited. We report the results of a study involving college-aged women with and without ID learning two different category structures - a rule-based and an information-integration structure - selected based on the putative differential role of dopamine in learning these two structures. ID non-anemic (IDNA) and iron-sufficient (IS) women completed 1200 learning trials for each structure. EEG was collected to assess the effects of ID on features affected by dopaminergic state: error-related negativity (ERN) and positivity (Pe), feedback-related negativity (FRN), and task-related blink rate. In addition, we examined the EEG data for dynamics distinguishing IDNA from IS women, including a measure of neural efficiency. Both groups of women were able to learn both structures. However, IDNA women were initially slower and less accurate than IS women, specifically for the rule-based structure. There were large and persistent group differences in brain dynamics and neural efficiency measures. The results are discussed with respect to the selective impact of ID on initial rule-based learning and the persistent effect of ID on dopamine signaling and energetic efficiency.