Serum Vitamin Status Profile and Cognitive Function in a National Sample of Older Americans

To the Editor: The relationship between vitamin status and cognitive function remains controversial because of the conflicting evidence available. Small samples and use of possibly biased, memory-dependent dietary recall data have limited most observational and experimental studies of vitamins and cognitive function in elderly adults. Studies on the relationship between serum nutrient concentrations, memory, and brain imaging indices show that study of nutrient patterns may be a more productive approach than study of single nutrients. In the current study, the association between a serum vitamin status profile and memory was examined in a large, national sample. The National Health and Nutrition Examination Survey (NHANES) examined a national sample of 3,128 persons aged 60 and older from 1991 to 1994, 2,308 of whom had complete data on serum concentrations of folate; vitamins B12, C, D, and E, beta-carotene; Boston Story-Recall Test (BST); and the Short Index of Cognitive Function (SICF). Similar to the Mini-Mental State Examination (MMSE), the SICF assesses capacity for calculation, registration, and recall. The BST assesses logical memory. A vitamin score (VS) was computed, giving one point each for each of six vitamin levels greater than the median. Dummy variables were created to indicate low (0–2), medium, and high (5–6) VS for regression analyses. Five percent of the sample had a VS of 0, 13.7% a score of 1, 18% a score of 2, 19.9% a score of 3, 16.8% a score of 4, 15.9% a score of 5, and 11.9% a score of 6. SICF scores of 0 to 11 were consistent with moderate to severe impairment (8.0%), 12 to 13 with mild impairment (8.0%), 13 to 16 with good function (36.8%), and 17 with excellent function (47.2%). Mean BST score showed an increase from VS = 0 to VS = 6 (7.7, 7.4, 7.8, 8.4, 8.0, 8.6, 8.5, respectively). In a linear regression model adjusting for age, a low VS was significantly associated with lower BST score (beta coefficient 1.13, P < .001), and a test for trend was significant (P < .001). After adjusting for age, sex, race, and years of education, a low VS remained significantly associated with lower BST score (beta coefficient 0.58, P = .006), and a test for trend was significant (P = .01) (Table 1). No interaction between VS and age or sex was seen. To assess factors associated with low SICF, a bivariate logistic regression model with SICF less than 11 as the outcome measure of interest was related to VS as the exposure variable. Compared with high VS, the odds ratio (OR) of a medium VS was 1.34 (95% confidence interval (CI) = 0.79–2.28, P = . 27) and of a low VS was 2.24 (95% CI = 1.07–4.67, P = .03). After controlling for age, sex, race and ethnicity, and education, ORs were 1.21 (95% CI = 0.65–2.24, P = .54) and 1.64 (95% CI = 0.69–3.90, P = .25), respectively. This study found a significant correlation between VS and BST but not SICF. Studies of individual vitamins and cognitive function have yielded variable results. These findings for SICF contradict those of previous studies, which found a relationship between certain vitamins and changes in brain mass or cognitive function in small, selected samples. The current study relied on two different methods of assessing cognitive function, BST and SICF, and a slightly different vitamin status profile and had no brain imaging data, although use of a large national sample makes these findings much more applicable to the U.S. noninstitutionalized, elderly population. In conclusion, VS was independently associated with BST but not SICF. Therefore, a protective effect on cognitive function in individuals with high serum levels of six vitamins, as previously reported in a small elderly sample, was only partially confirmed in a large national sample aged 60 and older.