Abstract
Evidence suggests that the rate of glucose release following consumption of carbohydrate-containing foods, defined as the glycaemic index (GI), is inversely associated with cognitive function. To date, most of the evidence stems from either single-meal studies or highly heterogeneous cohort studies. We aimed to study the prospective associations of diet GI at age 53 years with outcomes of verbal memory and letter search tests at age 69 years and rate of decline between 53 and 69 years. Longitudinal population-based birth cohort study. MRC National Survey for Health and Development. Cohort members (n 1252). Using multivariable linear and logistic regression, adjusted for potential confounders, associations of higher-GI diet with lower verbal memory, lower letter search speed and lower number of hits in a letter search test were attenuated after adjustments for cognitive ability at age 15 years, educational attainment, further training and occupational social class. No association was observed between diet GI at 53 years and letter search accuracy or speed-accuracy trade-off at 69 years, or between diet GI at 53 years and rate of decline between 53 and 69 years in any cognitive measure. Diet GI does not appear to predict cognitive function or decline, which was mainly explained by childhood cognitive ability, education and occupational social class. Our findings confirm the need for further research on the association between diet and cognition from a life-course perspective.
Highlights
When we examined change in cognitive function between ages 53 and 69 years by including the corresponding baseline cognitive function measures, no association between diet glycaemic index (GI) at age 53 years and change in either verbal memory score or letter search speed score was found
Similar results were found for letter search speed, where cognitive abilities at age 15 years (B = −0·88; 95 % CI −1·93, 0·18; P = 0·10) and education (B = −0·67; 95 % CI −1·74, 0·39; P = 0·22) each independently attenuated the association between diet GI and search speed, but not further training (B = −1·31; 95 % CI −2·35, −0·28; P = 0·01) and social class (SC) (B = −1·11; 95 % CI −2·16, −0·07; P = 0·03)
To the best of our knowledge, the present analysis is the first to investigate prospective associations between dietary GI, a measure of carbohydrate quality with potential effects on rate of glucose release[11], and cognitive function over later adulthood when cognitive decline is more evident, and lends further support to the possibility of such an association being confounded by childhood cognitive ability and adult-life socio-economic position
Summary
Participants The NSHD, known as the British 1946 birth cohort, is a socially stratified sample of 5362 individuals (2547 males and 2815 females) born during one week in March 1946 in England, Scotland and Wales[23]. All analyses were first performed unadjusted (model 1) and were adjusted for sex (model 2), further adjusted for cognitive abilities at age 15 years, education, training and SC (model 3), further adjusted for BMI, waist circumference, smoking status, physical activity, blood pressure, HDL-cholesterol, TAG and antihypertensive medication (model 4), and further adjusted for total energy intake, percentage of energy from fat, saturated fat, alcohol and carbohydrate, NSP (g/d) and EI:EER (model 5). To reduce potential bias from missing covariables, variables with missing values (i.e. cognitive abilities at age 15 years (nmissing 173), education (n 61), further training (n 114), SC (n 49), BMI (n 3), smoking (n 1), physical activity (n 1), blood pressure (n 17), HDL-cholesterol (n 224), TAG (n 151) and antihypertensive medication (n 1)) were imputed using multiple imputation to maximize the analytical sample. Statistical analyses were performed using the statistical software package IBM SPSS Statistics for Windows version 22.0 and P < 0·05 was considered statistically significant
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