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ORIGINAL RESEARCH COMMUNICATION |
1 From the Section of Preventive Medicine & Epidemiology, Evans Department of Medicine (LD and RCE), and the Department of Neurology (RHM), Boston University School of Medicine, Boston, and the Division of Epidemiology (JSP and DKA) and the Department of Laboratory Medicine and Pathology (JHE), University of Minnesota, Minneapolis
2 Supported by National Heart, Lung, and Blood Institute cooperative agreement grants U01 HL56563, HL56564, HL56565, HL56566, HL56567, HL56568, and HL56569; National Heart, Lung, and Blood Institute grant 5K01-HL70444; and National Institute on Alcohol Abuse and Alcoholism grant 1 R01 AA13304.
3 Address reprint requests and correspondence to L Djoussé, Boston University School of Medicine, Room B-612, 715 Albany Street, Boston, MA 02118. E-mail: ldjousse{at}bu.edu.
| ABSTRACT |
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4 is associated with an increased risk of cardiovascular disease. The presence of the
4 allele has been associated with lower concentrations of HDL cholesterol, but it is not known whether the
4 allele modifies the association between alcohol consumption and HDL-cholesterol concentrations.
Objective:The objective of the study was to assess whether the
4 allele modifies the association between alcohol consumption and HDL-cholesterol concentrations.
Design:In a cross-sectional design, we studied 670 men and women aged 2678 y who participated in the National Heart, Lung, and Blood Institute Family Heart Study to assess whether the
4 allele of the gene APOE modifies the association between alcohol consumption and HDL-cholesterol concentrations. Alcohol data were self-reported, and we used multivariate, generalized estimating equations to assess interactions.
Results:In a model with adjustment for age, sex, body mass index, smoking, exercise, waist-hip ratio, TV viewing, and study site, there was a significant effect of the interaction between the
4 allele and alcohol consumption on HDL cholesterol (P = 0.0001). In the absence of the
4 allele, multivariate adjusted means of HDL were 1.24, 1.36, and 1.54 mmol/L among subjects who never drank and those who currently drink 0.112 and >12 g alcohol/d, respectively; in the presence of the
4 allele, the corresponding values were 1.19, 1.27, and 1.25 mmol/L.
Conclusion:Our data show a significant effect of the interaction between the
4 allele and alcohol consumption on HDL. The increase in HDL associated with alcohol appears to be stronger in subjects without the
4 allele than in those with the
4 allele.
Key Words: Apolipoprotein E alcohol consumption interaction HDL cholesterol lipids
| INTRODUCTION |
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2,
3, and
4, respectively. APOE allele
4 has been associated with lower concentrations of HDL cholesterol (1216), increased risk of CAD (17, 18), and higher concentrations of LDL cholesterol (12, 15) and triacylaglycerol (12) concentrations. Data on possible interaction between alcohol consumption and HDL and LDL have been inconsistent (19, 20).
In the present study, we examined whether the
4 allele of APOE modified the association between alcohol consumption and HDL cholesterol concentration in 670 white participants in the National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study.
| SUBJECTS AND METHODS |
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The current analyses are based on the 670 white participants from the random sample with complete data on APOE genotype, alcohol consumption, and HDL cholesterol. The number of nonwhite subjects was inadequate for analysis.
Blood collection and assays
All participants were asked to fast for 12 h before their arrival at the study center. Evacuated tubes without additives were used to collect samples for lipids; blood samples were then spun at 3000 x g for 10 min at 4 °C. Sera were stored at 70 °C until they were shipped to a central laboratory at the Fairview-University Medical Center in Minneapolis for processing. APOE genotyping was performed by using polymerase chain reaction (PCR) to amplify a 267-bp fragment from exon 3 of APOE (23). The PCR product was digested with the HhaI restriction endonuclease (an isoschizomer of CfoI), which resulted in a specific banding pattern for the 3 isoforms of the Apo E protein when separated by polyacrylamide gel electrophoresis and silver stained. Total and HDL-cholesterol and triacylglycerol concentrations were measured by using a COBAS FARA high-speed centrifugal analyzer (Roche Diagnostic Systems, Montclair, NJ). HDL cholesterol was measured after precipitation of the other lipoprotein fractions with the use of dextran sulfate (24). For samples with triacylglycerol concentrations < 4.5 mmol/L (400 mg/dL), LDL cholesterol was calculated by using the Friedewald formula (25). For subjects with higher concentrations of triacylglycerol, LDL-cholesterol quantitation was performed on EDTA plasma by using ultracentrifugation.
Assessment of alcohol consumption
Information on alcohol consumption was obtained during the clinic interviews by asking whether the person ever consumed alcoholic beverages and whether he or she currently drinks any alcoholic beverages; if the subject answered yes to the latter question, he or she was asked specifically about the number of drinks of each type of alcoholic beverage consumed per week. Subjects who reported that they consumed alcohol in the past but currently were nondrinkers were classified as former drinkers. For purposes of the study, a "drink" was defined as a 360-mL bottle or can of beer containing 12.6 g alcohol, a 120-mL glass of wine containing 13.2 g alcohol, or a 37.5-mL shot of 80-proof spirits containing 15 g alcohol. Total alcohol was computed as sum of the 3 beverage-specific alcohol measurements. For these analyses, we considered a drink to contain
12 g alcohol. The reported total alcohol intake was highly correlated with serum gamma-glutamyltranspeptidase measured in a subsample of drinkers (r = 0.51, P < 0.0001).
Other variables
A staff-administered semiquantitative food-frequency questionnaire developed by Willett et al (26) was used to collect dietary information. The reproducibility and validity of this food-frequency questionnaire were documented elsewhere (27, 28). The intake of specific nutrients was computed by multiplying the frequency of consumption of an item by the nutrient content of specified portions. Composition values for nutrients were obtained from the Harvard University Food Composition Database derived from US Department of Agriculture sources (29) and manufacturer information.
Information on cigarette smoking and education was obtained by interview during the clinic visit. Level of physical activity during the previous year (total minutes of exercise per day) and the number of hours spent watching television each day were self-reported. Anthropometric data were collected while participants were wearing scrub suits. Diabetes mellitus was considered present if a subject was taking hypoglycemic agents, if a physician had told the subject that he or she had diabetes mellitus, or if fasting blood glucose was >7.0 mmol/L.
Statistical analyses
Apo E was measured in 754 of 2673 randomly selected study participants. We excluded 52 nonwhite subjects, because there were too few of that group for separate analysis. Of the remaining 702 participants, all of whom were white, 32 were excluded because they had the E2/E4 genotype (n = 17) or were currently undergoing treatment for hypercholesterolemia (n = 15). We used the chi-square test to ascertain whether APOE genotype distribution was in Hardy-Weinberg equilibrium. Because we did not observe an effect of a three-way interaction between sex, alcohol, and the APOE
4 allele on HDL cholesterol (P = 0.18), we present combined data for men and women. We excluded former drinkers before using generalized estimating equations (GEE). To evaluate the alcohol-Apo E interaction, we dichotomized Apo E on the basis of the presence or absence of the
4 allele and included the main effects of alcohol (continuous) and the
4 allele and the alcohol x
4 allele product term by using GEE (PROC GENMOD in SAS; SAS Institute Inc, Cary, NC). This model corrects the variance for familial clustering. The adjusted model controlled for age, sex, body mass index (BMI; in kg/m2), smoking, and exercise. In addition, we controlled for study site, waist-to-hip ratio, exogenous estrogen use by the female subjects, and hours of television watching. The full model also included education; energy intakes; intakes of dietary cholesterol, saturated and polyunsaturated fat, and fruit and vegetables; and history of diabetes mellitus. We also repeated these analyses by using Apo E to model different genotypes (E2/E2, E3/E3, E3/E4, and E4/E4). To estimate adjusted mean values of HDL-cholesterol concentration, we classified subjects as never drinkers or as current drinkers of 0.112 or >12 g alcohol/d. We then fitted GEE as described above. We repeated these analyses for LDL cholesterol and the ratio of total to HDL cholesterol. Sensitivity analyses were conducted in a sample excluding current drinkers consuming >30 g alcohol/d. In addition, we tested the robustness of the GEE by repeating the analyses in only one person per family. Significance level was set at 0.05. All analyses were performed by using SAS for WINDOWS software (release 8.02, WINDOWS 5.1; SAS Institute Inc, Cary, NC).
| RESULTS |
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4 and alcohol categories. Irrespective of the
4 allele, alcohol consumption was associated with male sex, current smoking, lower prevalence of diabetes, lower BMI, higher energy intake, and higher prevalence of physical activity (Table 2
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4 allele was independently associated with lower HDL-cholesterol concentration. Mean (± SE) HDL-cholesterol concentrations in subjects without the
4 allele (1.32 ± 0.02) were significantly higher than those in subjects with the
4 allele (1.20 ± 0.03) in a model with adjustment for age, sex, smoking, and alcohol (P < 0.0001).
We observed a significant effect of the interaction between alcohol consumption and the APOE
4 allele on HDL-cholesterol concentration (P = 0.0001) in a regression model after control for age, sex, BMI, smoking, exercise, waist-hip ratio, exogenous estrogen, television viewing, and study site. In the absence of the
4 allele, adjusted means of HDL cholesterol were 1.24, 1.36, and 1.54 mmol/L for never drinkers and current drinkers of 0.112 and >12 g alcohol/d, respectively (P for trend < 0.0001), in the full model (Table 3
). Corresponding values for subjects with the
4 allele were 1.19, 1.27, and 1.25 mmol/L, respectively (P for trend = 0.93; Table 3
). The observed results did not change when subjects consuming >3 drinks/d (>36 g alcohol/d) were excluded (P for interaction = 0.016). Further analysis restricted to subjects consuming
30 g alcohol/d did not alter our findings (P for interaction = 0.026). In the fully adjusted model, comparing never drinkers with current drinkers of >12 g alcohol/d, the net increase in HDL cholesterol was 0.30 mmol/L (11.6 mg/dL) in the absence of the
4 allele but only 0.06 mmol/L (2.3 mg/dL) in the presence of the
4 allele (Table 3
). To evaluate the influence of individual APOE genotypes, we tested the interaction between alcohol and Apo E by using a mixed model in SAS and found evidence for a significant effect of the interaction between Apo E and alcohol consumption on HDL (P for interaction = 0.04; P for main effects = 0.044 and 0.24 for alcohol and Apo E, respectively).
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4 allele and alcohol consumption on the ratio of total to HDL cholesterol (P for interaction = 0.0018 in a fully adjusted model; Table 3
4 allele and alcohol consumption on LDL cholesterol (P for interaction = 0.25; Table 3
4 allele on HDL cholesterol (P = 0.028) and total:HDL cholesterol (P = 0.032) but not on LDL cholesterol (P = 0.19). | DISCUSSION |
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4 allele of APOE on HDL-cholesterol concentration after adjustment for major confounding factors. In the absence of the
4 allele, the magnitude of increase in HDL cholesterol between never drinkers and current drinkers of >12 g alcohol/d was 0.30 mmol/L compared with only 0.06 mmol/L in the presence of the
4 allele. Of note is that, in the highest drinking category, the average alcohol intake among subjects with the
4 allele was 31.1 g/d (
2.5 drinks/d) and that among subjects without the
4 allele was 24.7 g/d (
2 drinks/d). This suggests that, if the average alcohol consumption was similar between subjects with the
4 allele and those without it, then, among subjects with the
4 allele, the magnitude of difference in HDL cholesterol between never drinkers and drinkers of >12 g alcohol/d would be even less than the observed difference if we assume a linear relation between alcohol and HDL-cholesterol concentrations. However, we observed a significant effect of the interaction between alcohol and the
4 allele on HDL cholesterol even after the exclusion of subjects consuming >30 g alcohol/d (>2.5 drinks/d). This suggests that our findings were not driven by an unbalanced distribution of heavy drinkers between subjects with and without the
4 allele.
In support of our findings, several studies have shown that the
4 allele of APOE is associated with lower concentrations of HDL cholesterol (1216). In contrast, the
4 allele had a nonsignificant association with HDL-cholesterol concentrations in another study (30). However, these latter data were unadjusted for potential confounders, and the trend was toward lower HDL-cholesterol concentrations in the presence of the
4 allele (30). Furthermore, the frequency of the
4 allele was relatively low (7.5% compared with 14% in this study) (30). In the Framingham Study, the
4 allele (present in 13.2%) was not associated with lower concentrations of HDL cholesterol after adjustment for age, BMI, and (in women) menopausal status (31).
Whereas it is established that alcohol consumption is associated with higher HDL-cholesterol concentrations (7, 9, 32), few studies have examined whether the APOE
4 allele modifies the alcohol-HDL cholesterol association. Corella et al (19) reported a significant interaction between alcohol consumption and APOE genotype on HDL cholesterol among men but not among women. In a Canadian study, whereas alcohol intake did not modify the association between BMI and HDL in subjects with the
3 allele, there was evidence for an effect of the interaction between alcohol and BMI on HDL among nonsmokers (33). The lack of interaction between alcohol and LDL in that study was consistent with findings of Corella et al (20) in men. However, the latter study found a significant effect of the interaction between alcohol and Apo E on LDL in women (20). Data from the Framingham Offspring Study showed a significant effect of the interaction between alcohol consumption and Apo E on LDL in men but not in women (19), and we have previously reported evidence for an effect of the interaction between Apo E and smoking on LDL (34). If confirmed in future studies, our findings suggest that alcohol consumption might increase HDL-cholesterol concentrations less in subjects with the
4 allele than in persons without the
4 allele.
Our study has some limitations. The interpretation of our results is limited by the cross-sectional design, which makes it difficult to ascertain the temporal relation between alcohol consumption and HDL-cholesterol concentrations. The data are limited to those from white subjects, and it is unclear whether similar results would be obtained in other ethnic groups. It is possible that subjects might have underreported their usual alcohol consumption; however, such bias is less likely to have been different between subjects with the
4 allele and subjects without it. The strong correlation between alcohol consumption and concentrations of gamma-glutamyltranspeptidasea biomarker of alcohol consumption (35)provides support for the validity of self-reported alcohol intake.
In conclusion, our data indicate an effect of the interaction between alcohol consumption and the APOE allele
4 on HDL-cholesterol concentrations in white men and women. This suggests that the beneficial effects of alcohol consumption on HDL cholesterol might be stronger in the absence of the
4 allele. Further studies are needed to test whether Apo E status modifies the beneficial effects of alcohol consumption on the risk of myocardial infarction.
| ACKNOWLEDGMENTS |
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LD designed this project, completed the data analyses, and prepared the manuscript; JSP participated in the data analyses and critically reviewed the manuscript; DKA participated in the study design, data collection, and critically reviewed the manuscript; JHE participated in the study design, data collection, measurement of HDL cholesterol, and critically reviewed the manuscript; RHM participated in the study design, data collection, and critically reviewed the manuscript; and RCE participated in the study design, data collection, data analyses, and critically reviewed the manuscript. RCE has received limited support for research in the past from companies in the alcohol beverage industry. None of the other coauthors had a conflict of interest.
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