Impact of high iron intake on cognition and neurodegeneration in humans and in animal models: a systematic review

CONTEXT: Accumulation of brain iron is linked to aging and protein-misfolding neurodegenerative diseases. High iron intake may influence important brain health outcomes in later life. OBJECTIVE: The aim of this systematic review was to examine evidence from animal and human studies of the effects of high iron intake or peripheral iron status on adult cognition, brain aging, and neurodegeneration. DATA SOURCES: MEDLINE, Scopus, CAB Abstracts, the Cochrane Central Register of Clinical Trials, and OpenGrey databases were searched. STUDY SELECTION: Studies investigating the effect of elevated iron intake at all postnatal life stages in mammalian models and humans on measures of adult brain health were included. DATA EXTRACTION: Data were extracted and evaluated by two authors independently, with discrepancies resolved by discussion. Neurodegenerative disease diagnosis and/or behavioral/cognitive, biochemical, and brain morphologic findings were used to study the effects of iron intake or peripheral iron status on brain health. Risk of bias was assessed for animal and human studies. PRISMA guidelines for reporting systematic reviews were followed. RESULTS: Thirty-four preclinical and 14 clinical studies were identified from database searches. Thirty-three preclinical studies provided evidence supporting an adverse effect of nutritionally relevant high iron intake in neonates on brain-health-related outcomes in adults. Human studies varied considerably in design, quality, and findings; none investigated the effects of high iron intake in neonates/infants. CONCLUSIONS: Human studies are needed to verify whether dietary iron intake levels used in neonates/infants to prevent iron deficiency have effects on brain aging and neurodegenerative disease outcomes.