Iron and vitamin D deficiencies are among the most common micronutrient disorders worldwide, yet their impact on cognitive function in working-age adults remains underestimated. This narrative review synthesises current evidence on neurobiological mechanisms linking these deficiencies to cognitive decline, psycho emotional disturbances, and reduced work productivity, focusing on latent deficiency states that escape routine diagnosis. Latent iron deficiency (low ferritin, normal haemoglobin) affects 40-55% of women of reproductive age, while vitamin D insufficiency (25(OH)D <20 ng/mL) is present in 30-50% of adults in northern latitudes and also in sunny regions where clothing limits skin exposure. Vegetarians, office workers, and residents of high-latitude countries are at the highest risk. Iron deficiency impairs dopaminergic signalling, myelin synthesis, and mitochondrial energy metabolism, leading to cognitive deficits. Vitamin D deficiency reduces neurotrophin expression, promotes neuroinflammation, and weakens antioxidant defence, resulting in executive dysfunction and slower processing. Both deficiencies contribute to anxiety, depression, apathy, and sleep disturbances. Cognitive decline begins at the stage of latent deficiency, before anaemia or osteomalacia develop, and is often misattributed to stress or ageing. Partial reversibility following iron repletion has been demonstrated, whereas the cognitive response to vitamin D supplementation is more modest and inconsistent. Screening for ferritin (target >50 μg/L) and 25(OH)D (target 30-50 ng/mL) is indicated in patients complaining of "brain fog", particularly in risk groups. Hidden hunger is a socially significant challenge that reduces economic productivity and quality of life.
