The effect of dietary magnesium intake on cognitive decline related to olfactory impairment in older adults: a cross-sectional study from the NHANES database

Olfactory impairment in the elderly has been shown to be associated with an increased risk of cognitive decline, and oxidative stress may be involved in this process. Dietary magnesium (Mg), as an antioxidant dietary nutrient, has been reported to be associated with cognitive decline. This study aimed to explore the effect of dietary Mg intake on cognitive decline related to olfactory impairment in older adults. Data were extracted from the National Health and Nutrition Examination Survey (NHANES) database 2013-2014. Information on dietary Mg intake was obtained from 24-hour interview. Assessment of cognitive decline included four evaluation dimensions: the Consortium to Establish a Registry for Alzheimer's Disease (including immediate and delayed), an animal fluency test, and a digit symbol substitution test. Weighted univariable and multivariable linear regression models were utilized to explore the effect of Mg on cognitive decline related to olfactory impairment, using β values and 95% confidence intervals (CIs). Subgroup analyses based on gender, history of diabetes, cardiovascular disease (CVD) and depression were further assessed. In total, 1,388 elderly people were included, of whom 319 (22.98%) had olfactory impairment. After adjusting for all covariates, there was an inverse relationship between high Mg intake and cognitive decline (β=-0.21, 95%CI: -0.37 to -0.04), and olfactory impairment was positively associated with cognitive decline (β=0.53, 95%CI: 0.28 to 0.77). Among the elderly with olfactory impairment, the odds of cognitive decline were reduced in the high Mg intake group (β=0.37, 95% CI: 0.04 to 0.71) compared to the low Mg intake group (β=0.67, 95%CI: 0.39 to 0.96), especially among the elderly who were female (β=0.53, 95% CI: 0.09 to 0.98), with diabetes (β=0.72, 95% CI: 0.46 to 0.99), and without CVD (β=0.33, 95% CI: 0.05 to 0.61) and depression (β=0.38, 95% CI: 0.06 to 0.70). Adequate dietary Mg intake may provide potential beneficial effects, improving cognitive function, among elderly patients with olfactory impairment, which should be confirmed by scale-large prospective studies.