The Influence of Iron Deficiency on Declarative, Procedural, and Working Memory

Abstract

Previous research has found that iron deficiency (ID) is associated with deficits in cognition, including aspects of memory. However, little has been done to identify specific aspects of memory that are negatively affected, mainly because most studies have not selected measures that are sensitive to changes in brain regions that are differentially dependent on iron. This study examined the influence of iron status on the learning of two types of memory (declarative and procedural memory) as well as the role of working memory. A total of 42 healthy female participants (ages 19-27 years), 22 iron deficient and non-anemic (IDNA) and 20 iron sufficient (IS), completed the memory tasks over separate days. IDNA participants had low iron stores (serum ferritin; sFt < 16 µg/L) and normal hemoglobin levels (Hb ≥ 12 g/L) and were matched with IS participants who had both normal iron stores and normal Hb (sFt > 16 µg/L). The declarative and procedural memory tasks involved learning to categorize simple stimuli based on two distinct categorical structures. These tasks were selected based on evidence that they (a) recruit brain regions with high reliance on iron and (b) differentially support the two types of memory. In addition, the working memory task was chosen based on previous findings demonstrating performance variations as a function of iron status and was also completed in a dual-task phase with the other memory tasks. The strongest results for group differences in learning and performance were for the declarative memory task, with some notable differences in response speeds for the procedural memory task. Significant correlations between performance and continuous iron status measures as well as group differences on the working memory task also provided evidence of the effect of ID on cognition. Behavioral performance was most sensitive to variations in iron status on the declarative task, with smaller but detectable impacts on the procedural and working memory tasks. The impacts of ID on memory, especially for declarative memory, are discussed with respect to general cognitive functioning and specific to a college-aged population.