The analyzed cohort of 3,718 community residents was 60% black and 62% female, and had a mean age of 74.3 years (range: 65 to 102) at baseline and a mean educational level of 12.2 years (SD: ±3.7).
Persons with high intakes of fruits and vegetables tended to have a favorable risk profile for health and cognition (). They were more likely to be female, to be white, to have more years of education, and to have higher levels of physical activity. The high fruit consumers, but not high vegetable consumers, were also somewhat more likely to have a cardiovascular-related condition, including myocardial infarction, hypertension, and diabetes.
Baseline characteristics* of 3,718 participants of the Chicago Health and Aging Project (CHAP)
The mean cognitive score at baseline for the cohort of 3,718 persons was 0.18 (range: −3.5 to 1.6). The overall mean change in cognitive score was a decline of 0.04 standardized units per year (SU/y).
The average total daily intake of both fruits and vegetables combined was 4.5 servings per day (range, 0 to 14.4). There was no association between combined fruit and vegetable intake and 6-year change in cognitive score in models that adjusted for age and total energy intake (p for trend = 0.28), or with additional control for sex, race, education, cognitive activity, physical activity, and alcohol consumption, although the differences in rates for upper quintiles compared with the first were in the positive direction indicating slower rates of decline (data not shown).
We next examined the rates of change in cognitive score by quintiles of vegetable intake. The average number of vegetable servings per day was 2.3, with a range of 0 to 8.2. When we adjusted for age and total energy intake, we observed a marginally significant association of slower cognitive decline with higher intake (p for linear trend = 0.06) (). The association became stronger when we added control for sex, race, education, cognitive activity, physical activity, and alcohol consumption (p for trend = 0.04). Compared with a cognitive decline rate of −0.046 SU/y for persons in the first quintile of vegetable intake (median of 0.9 servings/day), the rates were −0.030 SU/y for persons in the fourth quintile (median, 2.8 servings/day), and −0.032 SU/y for persons in the fifth quintile (median 4.1 servings/day). The difference of 0.016 between the fourth and first quintiles represented a 35% reduction in annual rate of cognitive decline. The difference of 0.014 with the fifth quintile represented a 30% reduction, although the difference was marginally significant.
Figure Annual rates of change and differences in the rates (p value) by quintile of fruit and vegetable intake based on random effects models of 3,718 persons with cognition measured at three time points over 6 years, Chicago Health and Aging Project, 1993–2002. (more ...)
In separate analyses we added terms for cardiovascular-related conditions, including history of stroke, heart disease, hypertension, and diabetes, as these conditions may serve as confounders or as the intermediate mechanisms through which vegetable consumption is associated with slower cognitive decline. However, the rate differences were not materially changed (rate differences were 0.015 [p = 0.04] for the fourth quintile and 0.014 [p = 0.09] for the fifth quintile, compared with the first; p for linear trend = 0.05).
Daily servings of fruit intake for the cohort ranged from 0 to 8.5 servings per day, with an average of 2.2. There was no evidence of association between fruit intake and cognitive change in either the age- or the multiple-adjusted models (). The rate differences between upper quintiles of intake compared with the first fluctuated around zero, and became even smaller with further control for all other potential confounding variables.
We investigated in two ways whether the fact that some persons completed the FFQ after the baseline interview had any effect on our findings. First, we repeated the analyses with the addition of a variable that represented the number of days the FFQ was completed after the baseline, but there was virtually no change in the rate differences or p values for significance. Second, we created an indicator variable to identify persons who completed the FFQ within 1 year after baseline cognitive testing and re-analyzed the multiple-adjusted models with multiplicative terms between the indicator variable and quintiles of vegetable and fruit intakes. There were no significant differences in the rates of change for vegetable intake among persons who completed the FFQ within 1 year after baseline and those who completed it more than 1 year after baseline. However, persons who completed their FFQ close to baseline and who had high fruit intake (fourth and fifth quintiles) had significantly greater rates of decline than persons who had high fruit intake and completed their FFQ later than 1 year after baseline.
We next repeated the analyses after excluding persons whose baseline cognitive scores were in the bottom 10% of the distribution. The multiple-adjusted rate differences for persons in the fourth and fifth quintiles of vegetable intake changed little (β = 0.015; p = 0.05 and β = 0.014; p = 0.10) and the test for trend was marginally significant. There were no material changes in the rate differences of cognitive decline by quintile of fruit consumption, which remained non-significant.
We also examined the data for modifications in the rate differences by the demographic variables, age, sex, race, and education in separate multiple-adjusted models for both fruit and vegetable intake. The only evidence of effect modification was between vegetable intake and age, such that the association of slower decline with higher vegetable intake was stronger among persons of older age. In each of the third through fifth quintiles of vegetable intake, for each additional year of age, there was a reduction in the rates of cognitive decline by more than 0.002 SU/y (all p values < 0.03). The observed inverse association of cognitive decline with vegetable consumption and the absence of association with fruit consumption were not modified according to whether persons consumed a vitamin supplement (43% were taking a multivitamin or vitamin E or vitamin C supplement), currently smoked (15%), or reported a history of stroke (9%), or any cardiovascular-related condition (64%).
In previous studies, we found associations between cognitive change and individual dietary components, including vitamin E intake from foods, total vitamin C, niacin, folate, fish, and fat composition. When we adjusted for each of these dietary components in separate multiple-adjusted models, there was little difference in the effect estimates except for the models that included terms for vitamin E in food and different types of fat intake. In the model adjusted for vitamin E, the rate difference for the fifth vs first quintile of vegetable intake was modified to 0.12 and no longer significant. When we adjusted for dietary intakes of saturated (g/day), transunsaturated (g/day), and polyunsaturated fats (g/day) the difference in rate for the fifth quintile of vegetable intake was 0.014 (p = 0.10).
We next investigated cognitive decline according to intake of specific types of vegetables and citrus fruits in multiple-adjusted models (). All types of vegetables, except legumes, were inversely associated with cognitive decline. Green leafy vegetables had the highest consumption of all vegetable categories, and also had the strongest linear association (p for linear trend = 0.03). Analyses of each individual fruit and vegetable food item in separate multiple-adjusted models revealed a number of individual foods with statistically significant inverse associations, including zucchini/summer squash/eggplant, broccoli, lettuce/tossed salad, and greens/kale/collards (data not shown).
Table 3 Multiple-adjusted differences in the rates of cognitive change (p value) by quintile of fruit and vegetable intake based on multiple-adjusted random effects models of 3,718 persons with cognition measured at three time points over 6 years, Chicago Health (more ...)