Low Dietary Intakes of Vitamin K and Leafy Green Vegetables Are Individually Associated With Low Cognitive Functioning in A National Sample of U.S. Older Adults

Abstract

ObjectivesThis study aimed to examine the individual associations between dietary intake of vitamin K and leafy green vegetables with cognitive functioning in the US population of adults aged 60 years or older. MethodsCross-sectional data of older adults (≥60years; n = 2,342) from the 2011–2014 NHANES were analyzed. Dietary data were assessed by two 24-hour dietary recalls. ‘Low intake of vitamin K’ was defined as below the recommended daily intake (RDI) (i.e.,< 90mcg for women, < 120mcg for men). ‘Low intake of leafy green vegetables’ was defined as consuming below 90gr a day of green vegetables (e.g., broccoli, asparagus, green pees and beans) and below 30gr a day of leafy greens (e.g., kale, spinach, celery, and lettuce). The cognitive functioning assessment included four separate tests and their ‘overall score’: (1) The Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) word learning test; (2) Delayed Word Recall (DWR); (3) the Animal Fluency Test (AFT); (4) the Digit Symbol Substitution Test (DSST). Low cognitive functioning was defined as receiving the lowest 20th percentile on each test score. Weighted logistic regressions examined the study aims by tests while controlling for associated covariates: age, sex, race/ethnicity, socioeconomics, body mass index, lifestyle factors, energy intake, chronic diseases, and antithrombotic medication. ResultsMore than half of the sample (55%) did not consume sufficient intake of vitamin K a day, and about two thirds (66%) were defined as having low intake of leafy green vegetables. The multivariable model showed that participants with low intake of vitamin K are more likely, by 45–111%, to have low cognitive functioning than those with sufficient intake of vitamin K (overall score: Odds Ratio (OR) = 1.75, 95% CI: 1.36–2.26). Participants with low intake of leafy green vegetables had higher odds of having low cognitive functioning in three tests (i.e., CERAD, DWR, AFT) (ORs = 1.40–1.57) and in the overall test score (OR = 1.46, 95% CI: 1.14–1.87) than those who consumed ≥90 gr of green vegetables or ≥30 gr of leafy greens a day. ConclusionsLow intakes of dietary vitamin K and leafy green vegetables might be linked with cognitive function impairment in older adults. The causality of such associations needs to be examined using prospective study design or interventions. Funding SourcesN/A.