Higher dietary intakes of potassium, calcium and magnesium are associated with a reduced risk of developing vascular dementia

QUESTION Question: Do the dietary intakes of potassium, calcium and magnesium affect the risk of developing dementia in Japanese adults? People: In total, 1081 adults participating in the Hisayama study aged 60 years or older who did not have dementia at the start of the study and for whom information on dietary intakes was available. Setting: Hisayama, Japan; December 1988 to November 2005. Risk factors: Dietary intakes of potassium, calcium and magnesium. This was calculated from a semiquantitative food frequency questionnaire completed before the start of the study. Individuals were split into quartiles of consumption, with those in the lowest consumption quartile acting as the reference group. Information on medical history, antidiabetic and hypertensive treatments, educational status, alcohol consumption, smoking and physical activity were also collected. Blood pressure, height and weight were measured. Analyses were adjusted for age, sex and the other potential confounders measured. Outcomes: Dementia. Annual health examinations were performed and a daily monitoring system was established. Comprehensive screening for cognitive function including neuropsychological tests was carried out at 4, 10 and 17 years' follow-up. Dementia was diagnosed using DSM-IIIR criteria. Alzheimer's disease was diagnosed using the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's disease and Related Disorders Association criteria, and participants with vascular dementia were diagnosed with the criteria of the National Institute of Neurological Disorders and the Association Internationale pour la Recherche et l'Enseignement en Neurosciences. METHODS Design: Prospective cohort study. Follow-up period: 17 years. MAIN RESULTS During the 17-year follow-up, 303 participants developed dementia. A total of 166 participants developed Alzheimer's disease, 98 developed vascular dementia; 25 people with AD and 18 people with vascular dementia had another subtype of dementia as well. Participants in the highest quartile of potassium consumption were significantly less likely to develop dementia than those with the lowest consumption (HR 0.52, 95% CI 0.30 to 0.91), with a significant trend for decreasing risk with increasing consumption (p=0.02). Participants in the highest quartile of calcium consumption were borderline significantly less likely to develop dementia compared with those with the lowest consumption (HR 0.64, 95% CI 0.41 to 1.00), with a significant trend for decreasing risk with increasing consumption (p=0.04). Overall, there was a significant trend for decreasing risk of dementia with increasing magnesium consumption (p=0.04), but the risk of developing dementia in the highest quartile was not significantly different from that in the lowest quartile after adjustment for confounders (HR 0.66, 95% CI 0.40 to 1.01). Significant reductions in the risk of vascular dementia were found with highest quartiles of intakes of potassium (HR 0.20, 95% CI 0.07 to 0.56), calcium (HR 0.24, 95% CI 0.11 to 0.53) and magnesium (HR 0.26, 95% CI 0.11 to 0.61). Intake of these minerals was not significantly associated with the risk of developing Alzheimer's disease. CONCLUSIONS Higher self-reported dietary intake of potassium, calcium and magnesium in older adults in Japan is associated with a reduced risk of developing vascular dementia, but not Alzheimer's disease.