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ORIGINAL RESEARCH COMMUNICATIONS |
1 From the Section of Preventive Medicine & Epidemiology, Evans Department of Medicine, Boston University School of Medicine (LD, LLM, and CE); the Division of Epidemiology, University of Minnesota, Minneapolis (DKA); the Department of Psychiatry, University of Utah, Salt Lake City (HC); and the Division of Biostatistics, Washington University, St Louis (MAP).
2 Supported in part by the National Heart, Lung, and Blood Institute (cooperative agreement grants U01 HL56563, U01 HL56564, U01 HL56565, U01 HL56566, U01 HL56567, U01 HL56568, and U01 HL56569). 3 Reprints not available. Address correspondence to L Djoussé, Boston University School of Medicine, Room B-612, 715 Albany Street, Boston, MA 02118-2526. E-mail: ldjousse{at}bu.edu.
| ABSTRACT |
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Objective: The objective was to determine whether a high intake of fruit and vegetables is inversely associated with LDL concentrations.
Design: We used data collected from 4466 subjects in the National Heart, Lung, and Blood Institute Family Heart Study to study the association between fruit and vegetable consumption and serum LDL. We used a food-frequency questionnaire to assess fruit and vegetable intakes and regression models to estimate adjusted mean LDL according to fruit and vegetable consumption.
Results: The mean (±SD) age of the men (n = 2047) was 51.5 ± 14.0 y and that of the women (n = 2419) was 52.2 ± 13.7 y. The average daily serving of fruit and vegetables was 3.2 ± 1.7 for men and was 3.5 ± 1.8 for women. Fruit and vegetable consumption was inversely related to LDL: in the categories 01.9, 2.02.9, 3.03.9, and
4 servings/d, multivariate-adjusted mean (95% CI) LDL concentrations were 3.36 (3.28, 3.44), 3.35 (3.27, 3.43), 3.26 (3.17, 3.35), and 3.17 (3.09, 3.25) mmol/L, respectively, for men (P for trend < 0.0001) and 3.35 (3.26, 3.44), 3.22 (3.14, 3.30), 3.21 (3.13, 3.29), and 3.11 (3.04, 3.18), respectively, for women (P for trend < 0.0001). This association was observed across categories of age, education, smoking status, physical activity, and tertiles of Keys score. Exclusion of subjects with prevalent diabetes mellitus or coronary artery disease did not alter these results significantly.
Conclusion: Consumption of fruit and vegetables is inversely related to LDL in men and women.
Key Words: LDL fruit vegetables lipids National Heart Lung and Blood Institute Family Heart Study
| INTRODUCTION |
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7%. In a randomized trial, fruit and vegetable intake was associated with a reduction in LDL among patients with acute myocardial infarction after 12 wk of intervention (8). Fruit and vegetables are rich in dietary fiber, which has been shown to decrease LDL concentrations (911). In the current study we used data from 4466 adult participants of the National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study to evaluate whether higher intakes of fruit and vegetables is inversely related to LDL concentrations in men and women, independent of other risk factors.
| SUBJECTS AND METHODS |
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Blood collection and assays
Fasting blood samples for lipid measurements were collected into evacuated tubes containing no additives. Blood samples were then spun at 3000 x g for 10 min at 4 °C. Sera were stored at -70 °C until shipped periodically to a central laboratory at the FairviewUniversity Medical Center in Minneapolis for processing. LDL was estimated by using the method of Friedewald et al (13), except for subjects with triacylglycerol concentrations >400 mg/dL, whose LDL concentrations were measured by ultracentrifugation.
Assessment of fruit and vegetable intakes
Trained interviewers obtained information on usual consumption of fruit and vegetables with the use of a 100-item food-frequency questionnaire (FFQ) modified from the FFQ developed by Willett et al (14, 15). The reproducibility and validity of the FFQ was documented elsewhere (16). For fruit consumption, each participant was asked about how often, on average, he or she consumed fruit during the previous year (items 9 through 14 on the FFQ). For vegetable consumption, subjects were asked about their average consumption of vegetables such as beans, broccoli, cabbage, cauliflower, carrots, corn, spinach, squash, and tomatoes (items 15 through 25 on the FFQ). Response categories ranged from almost never, 13/mo, 1/wk, 24/wk, 56/wk, 1/d, 23/d, 46/d, to >6/d. The portion size of each fruit and vegetable was specified to facilitate determination of the number of typical servings and nutrient content.
Other variables
Information on the dietary consumption of total fat, saturated fat, and cholesterol was obtained by using the same FFQ. Intake of specific nutrients was computed by multiplying the frequency of consumption of an item by the nutrient content of specified portions. Nutrient composition was obtained from the Harvard University FOOD COMPOSITION DATABASE, derived from US Department of Agriculture sources (17), and from manufacturer information.
Anthropometric data were collected while the subjects were wearing scrub suits. A balance scale was used to measure body weight, and height was measured with a wall-mounted vertical ruler. Demographic data and information on alcohol intake, cigarette smoking, and physical activity (minutes per day of leisure activity) were obtained by interview.
Statistical analysis
Because eating habits differ between men and women, we initially analyzed the data stratified by sex and created the following categories of fruit and vegetable consumption: 01.9, 2.02.9, 3.03.9, and
4 servings/d. Because the subjects were not independent in this study, we used a general linear model (PROC MIXED; SAS Institute, Cary, NC) to estimate adjusted mean LDL concentrations across categories of fruit and vegetable intake. This method corrects the variance of the point estimates for familial clustering. Adjustment was made for age, age squared, study center, risk group (high risk compared with random), body mass index, energy intake (quintiles), smoking status (never, former, and current smokers), dietary cholesterol (quintiles), history of coronary artery disease, and diabetes mellitus. Additional adjustment for education (high school graduate or less, vocational school, and college or more), physical activity (minutes per day of leisure activity), use of vitamin supplements, consumption of breakfast cereals, and total fat (quintiles), saturated fat (quintiles), and polyunsaturated fat (quintiles) intakes did not alter the results significantly. All sex-specific analyses were initially conducted within the random and high-risk groups separately, but, because the results were similar, we combined the high-risk and random groups.
Subjects with higher intakes of fruit and vegetables were older and had different lifestyle habits and lower Keys score than did those who consumed fewer servings of fruit and vegetables per day. The Keys score correlates changes in fatty acid intake with changes in serum cholesterol and is computed as follows:
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60 y), tertiles of Keys score, education (high school graduate or less, vocational school, and college or more), smoking status (current nonsmokers and current smokers), physical activity (with the median of total minutes of daily exercise as the cutoff), and use of vitamin supplements. Furthermore, we repeated the analyses after excluding 751 subjects (n = 276 with diabetes mellitus, n = 366 with coronary artery disease, and n = 109 with both diseases). All analyses were performed with the use of SAS software (18). | RESULTS |
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4 servings of fruit and vegetables per day, adjusted mean (±SE) LDL concentrations were 3.36 ± 0.04, 3.35 ± 0.04, 3.26 ± 0.04, and 3.17 ± 0.06 mmol/L, respectively, in men (P for trend < 0.0001) and 3.35 ± 0.05, 3.22 ± 0.04, 3.21 ± 0.04, and 3.11 ± 0.04 mmol/L, respectively, in women (P for trend < 0.0001) in a model that adjusted for age, age squared, field center, risk group, body mass index, energy intake, smoking status, dietary cholesterol, and prevalence of diabetes mellitus and coronary artery disease (Table 3
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| DISCUSSION |
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67% lower than those in the lowest fruit and vegetable intake groups. Although several clinical trials and observational studies have assessed the effects of dietary fat on LDL concentrations, limited data are available on the association between the consumption of fruit and vegetables and LDL concentrations in a community-based population. In the DASH trial, LDL-cholesterol concentrations in 146 subjects assigned to consume a fruit and vegetable dieta diet increased in fruit, vegetables, and whole grains and lower in sweetswere not significantly lower than concentrations in the control group after an 8-wk intervention period (6). In that study, although the DASH dietwhich is rich in fruit, vegetables, and low-fat dairy products and low in saturated fat, total fat, and cholesterolresulted in a reduction in LDL cholesterol (mmol/L) in men [
change: -0.43 (95% CI: -0.60, -0.26)] and in women [-0.14 (-0.31, 0.03)], a diet high in fruit and vegetables indicated a nonsignificant reduction in LDL cholesterol (mmol/L) in men [-0.12 (-0.29, 0.05)] and no effect in women [0.05 (-0.12, 0.23)]. In contrast, the Indian Diet Heart Study showed that fruit and vegetable consumption was associated with a 7.3% decrease in LDL after 12 wk of intervention (7). However, this study did not analyze the data stratified by sex; of the 621 participants, only 14% were women. Neither the DASH trial (6) nor the Indian Diet Heart Study (7) assessed a dose-response effect between fruit and vegetable consumption and LDL-cholesterol concentrations. Fornes et al (19) reported in a cross-sectional study that the intake of fruit and vegetables was inversely correlated with LDL-cholesterol concentrations, and other investigators reported beneficial effects of fruit and vegetable intakes on LDL-cholesterol concentrations (20, 21). Our findings are consistent with these reports.
Diets rich in fruit and vegetables are good sources of dietary fiber. In a randomized trial, a fiber-multivitamin combination resulted in a reduction in LDL cholesterol of
8% from baseline after 8 wk (22). Other epidemiologic studies (9, 11) and a meta-analysis (23) showed LDL-cholesterol lowering effects of dietary fiber.
Our study has some limitations. Given the cross-sectional design, we cannot infer causality between fruit and vegetable consumption and lower concentrations of LDL cholesterol. However, dietary patterns in adults are relatively stable, and the exclusion of those with prevalent coronary artery disease and diabetes mellitus did not alter the results significantly, making it more likely that dietary intakes reported over the past year may reflect the subjects' usual diets. Frequencies of fruit and vegetable consumption were self-reported; thus, reporting bias might have affected our estimates of the effect.
Could the observed inverse association between fruit and vegetable consumption and LDL-cholesterol concentrations simply be attributed to a lower intake of saturated fat and dietary cholesterol in subjects with higher fruit and vegetable intakes? Our data indicate that a higher intake of fruit and vegetables was associated with lower Keys score and a lower percentage of energy from saturated fat, especially in men. This suggests that residual confounding by saturated fat could have biased our estimates. However, dietary cholesterol did not differ across categories of fruit and vegetable intakes in men and was in the opposite direction in women, because a higher intake of fruit and vegetables was related to higher dietary cholesterol in women (Table 2
). In addition, the inverse association between fruit and vegetable consumption and LDL-cholesterol concentrations was observed across all tertiles of Keys score and among subjects whose energy intake from saturated fat was above the 75th percentile of the total population. This finding is not consistent with the fact that subjects with a higher intake of fruit and vegetables were more likely to eat less saturated fat and dietary cholesterol. Thus, our findings are less likely to be attributable to the effect of substituting saturated fat and dietary cholesterol with fruit and vegetables. The wide age range, the availability of data across many centers, and the large sample size are strengths of the study. In conclusion, our data show that the consumption of fruit and vegetables is associated with lower concentrations of LDL cholesterol in a dose-response manner.
| ACKNOWLEDGMENTS |
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LD designed the project, completed the data analyses, and drafted the manuscript. DKA and MAP participated in the study design, the data collection, and the critical review of the manuscript. HC and LLM participated in the data analyses and the critical review of the manuscript. RCE participated in the study design, the data collection, the data analyses, and the critical review of the manuscript. None of the authors had a conflict of interest to disclose.
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