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Original Paper |
University of Cincinnati College of Medicine, Biostatistics Division (P.S.G.), Jewish Hospital of Cincinnati, Ohio
Cholesterol Center (P.W., C.J.G.), Jewish Hospital of Cincinnati, Ohio
Address reprint requests to: C.J. Glueck, MD, FACN, Cholesterol Center, Jewish Hospital, 3200 Burnet Ave, Cincinnati, OH 45229
| ABSTRACT |
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Methods: Using NHEFS 16 year follow-up data (1971 to 1987), we studied 5811 subjects, 1958 with and 3853 without CHD events, using logistic regression.
Results: In age groups 40 to 49, 50 to 59, 60 to 69, and 70 to 74 years (at study entry in 19714), the numbers of men and women were respectively 597 and 1019, 570 and 619, 932 and 1042, and 486 and 546. The following factors were independently positively associated (p<.05) with CHD: age, serum cholesterol, body mass index, cigarette use, and region (Midwest, Northeast). The following factors were independently negatively associated (p<.05) with CHD: gender (female), race (black), fish intake, alcohol, high school education, moderate exercise, and moderate and heavy habitual physical activity. Subjects with serum cholesterol >249 mg/dl benefitted less (p=.04) from fish intake than those with 209 to 249 or <209, and benefitted less (p=.03) from alcohol intake (CHD incidence [%]):
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Key words: coronary heart disease, fish, alcohol, serum cholesterol
| INTRODUCTION |
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Our specific aim in the 16-year longitudinal assessment of 5,811 subjects in the NHANES I epidemiologic follow-up study (NHEFS) [15] was to prospectively assess the important roles of modifiable dietary and behavioral characteristics in the causation and prevention of coronary heart disease.
| METHODS |
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Cholesterol Measurement.
All blood samples for measurements of serum total cholesterol were quantitated at a single centralized laboratory [5] to avoid between-laboratory variation. Only total cholesterol was assessed in our current report since HDL cholesterol and triglyceride levels were not measured.
Study Population.
The total sample in NHANES I (19711974) included 20,749 persons [3]. In the 19711974 initial screening for NHANES I, 14,407 subjects were examined ages 2574, and at the 16 year follow-up in 1987 of those ages 25 to 74 in 19711974, 11,018 (77%) were traced. Of these 11,018 subjects, 8721 had complete data sets for the variables of interest in the current analysis. Of those who were age 40 to 74 at the initial exam in 19711974, 5811 (with complete data sets, not using any special diets) were analyzed in 16 year follow-up (now ages 56 to 90 years) for evaluation of coronary heart disease morbidity and mortality, providing a total of 69,158 person years. In age groups 40 to 49, 50 to 59, 60 to 69, and 70 to 74 years (at study entry in 19714), the numbers of men and women were respectively 597 and 1019, 570 and 619, 932 and 1042, and 486 and 546. The number of subjects identified as Asians was very small, 9 Chinese and 10 Japanese.
To reduce the possibility of extraneous conclusions due to changes in diet caused by, or as a consequence, of disease discovery [7], we excluded all subjects who, by questionnaire response, had been using any special diet including those designed to reduce CHD risk, providing a cohort of 5,811 subjects. We did not exclude subjects taking antioxidant vitamins or estrogens; estrogen use was not included in the NHEFS data tape. Of these 5,811 individuals with 16 year follow-up, 3,853 (66%) had no hospitalizations or death from coronary heart disease, whereas 1,958 (34%) had CHD hospitalization or death. Cause-specific mortality [6] was determined from death certificates (ICD-9 codes 410414, 420441 with ICD 410414 for coronary heart disease). Hospitalizations were also coded by ICD-9, and codes 410414 and 420441 were likewise included as events for cardiovascular and coronary heart disease.
Statistical Methods
The dependent variable of interest was cardiovascular and coronary heart disease mortality and hospitalization.
The explanatory variables [1] included age, sex, race, serum total cholesterol, poverty class (poverty index divided by tertiles), ethnic group (Hispanic, other European, Black, American Indian, Asian, other), geographic region (Northeast, Midwest, West, South), and urban class (urban, suburban, rural). The poverty index consists of income divided by the number of persons in the household. Additional explanatory variables included log body mass index (BMI), cigarette use, education level of the head of household, leisure time exercise (little or none, moderate or much), and habitual physical activity (little, moderate, much). NHEFS did not obtain data on the waist/hip ratio.
Information was collected on specific food items (i.e., fish, milk, fruit, legumes, desserts cheese etc). Legume intake included peas, beans, peanuts, and peanut butter. Desserts included cakes, pies, cookies, puddings, and ice cream. The NHEFS data tape did not uniquely identify vegetarians. We included food groups in our analytical models as explanatory variables. Demographic variables were included in all models along with the other variables. Interactions among the explanatory variables were included in the multiple regression calculation.
Since age is a powerful predictor of hospitalization for CHD and vascular disease [1], it was modeled by grouping within decades.
The relative risks of the various CHD risk factors were adjusted by analysis of covariance for the other explanatory variables. Hence, a statistically significant relative risk is independent of the other explanatory variables effect on CHD (Fig. 1a, 1b, 1c).
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Each of the food items, including fish, bread, dessert, cheese, and alcohol, were recorded in one of four frequency categories: none; less than 1/week; 1 to 6 times/week; one or more times/day. For any of these food items, whenever the category increases by one level (e.g., from <1/week to 1 to 6 times/week), with all other variables unchanged, the risk of CHD (denoted by "r") then becomes "r" times as large as before,Fig. 1c.
The regression models allowed interaction terms for all of the above explanatory variables to enter into the models, but multi-way interactions could not be included due to limitations on model size.
| RESULTS |
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Significant Independent Determinants of Coronary Events
As displayed in Fig. 1a, b, and c, significant independent variables in the stepwise logistic regression positively associated with CHD events included, age, geographic region, serum cholesterol, cigarette smoking, body mass index, and bread intake.
Significant independent variables inversely associated with CHD events included race, female sex, education of the head of the household, alcohol intake, habitual exercise, physical activity, fish, cheese, and dessert intake (Fig. 1a, b, c).
There was a fish*serum cholesterol interaction (
2=4.2, p=.04, 1df) (Fig. 2). The lowest percentage of people who developed coronary heart disease over the 16 year follow-up (26%), were those who ingested fish one or more times/week and had serum cholesterol <209 mg/dl (Fig. 2). In contrast, those with no fish intake and serum cholesterol >249 mg/dl had a 45% likelihood of sustaining CHD over the 16 year follow-up period (Fig. 2).
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2=4.74, p=.03, 1 df) (Fig. 3). The lowest cardiac event rate (23%) was seen in subjects who took alcohol 1 to 6 times a week and had serum cholesterol <209 mg/dl, with higher event rates (41%) in those who took no alcohol and had serum cholesterol >249, or (42%) in those who took one or more alcoholic beverage/day and had serum cholesterol >249 mg/dl (Fig. 3).
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2=5.1, p=.025, 1 df) (Fig. 4). In the 40 to 49 year old age group, CHD events rose in the 1 to 6/week and
1/day alcohol intake groups. In the 50 to 59 and 60 to 69 year old age groups, CHD events fell with increasing alcohol through the 1 to 6 beverage/week category (Fig. 4).
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There was a region*exercise interaction such that in the Northeast or South, CHD fell as exercise levels rose (p=.03, .013).
There was a weight change*work interaction such that in blue collar workers, CHD events rose as weight increased (p=.016).
There were no other consistent, significant interactions for CHD event rates.
| DISCUSSION |
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The inverse associations of fish intake with CHD events, revealed again in the current study, are not new [2931]. However, the interactions of fish intake with serum cholesterol revealed in the current study appear to be more unique. Within "low" (<209 mg/dl), "midrange" (209 to 249 mg/dl), and "high" serum cholesterol (>249 mg/dl) categories, as fish intake rose, CHD events fell. There were, however, no "silver bullets", i.e., high fish intake did not negate high serum cholesterol. On the other hand, the lowest CHD event rate (26%) was seen in subjects with fish intake
1/week and serum cholesterol <209, suggesting that the benefits of low saturated fat, low cholesterol diet (with resultant low serum cholesterol) might be amplified by high fish intake.
The inverse associations of alcohol intake with CHD events, revealed again in the current study, are also not new [3234]. However, the interactions of alcohol intake with serum cholesterol appear to be more unique. For serum cholesterol categories <209 and 209 to 249 mg/dl, CHD event rates were highest for non-drinkers and lowest for those taking 1 to 6 alcoholic beverages/week. As was the case for fish intake, there were no "silver bullets", i.e., high alcohol intake was not protective when serum cholesterol was >249 mg/dl. Moreover, for all serum cholesterol categories, alcohol had a "U" shaped relationship with CHD events, with CHD events higher for both non-drinkers and for those ingesting
1 alcoholic beverage/day.
The significant inverse association of cheese intake with CHD events is puzzling, since increased cheese intake suggests increased saturated fat and cholesterol intake which would normally be expected to increase CHD event rates.
Approximately one-third of the saturated fatty acids in American diet come from dairy products [35]. It has been suggested that the type of saturated fats found in dairy foods raises total and LDL cholesterol more so than beef or cocoa butter saturated fats [35]. Despite these properties [35], consumption of cheese was negatively associated with the development of CHD in the NHEFS. It is possible that socioeconomic status is related to increased cheese and dessert consumption, and that affluent, educated subjects, known to have low CHD event rates [36], are eating more cheese and dessert, also inversely associated with CHD events in the current study. Despite covariance adjustment for socioeconomic status, cheese intake might, speculatively, still reflect some socioeconomic status effect. It is interesting to note that Danish volunteers fed a "heart healthy diet" which did not contain high fat cheese had cravings for cheese during the dietary intervention. Once returned to their habitual diet of choice, serum cholesterol increased to pre-intervention levels due to the inclusion of cheese in the diet [37].
It is possible that saturated fat intake might be more atherogenic in certain ethnic groups. In the current study, butter intake was positively associated with CHD event rates in subjects with pigmented skin, African-Americans, American Indians, Hispanics, and Asians, but not in Caucasians.
We speculate that lacto-ovo-vegetarians in the NHEFS population, known to have lower CHD event rates than omnivores [38,39], contributed to the inverse association of cheese with CHD. In longitudinal studies of Seventh Day Adventists, there was no difference in relative risk of heart disease in those with high and low frequency of cheese and dairy product consumption [4042]. Vegetarian diets that include cheese are able to lower cholesterol levels equally compared to cholesterol lowering diets that include meat [43]. Lifetime studies of cohorts of lacto-ovo vegetarians (Seventh Day Adventists in California) produced significant negative relationships to mortality rates from green salad consumption and a significant positive relationship for meat and egg consumption [42]. Within Seventh Day Adventists [42], as in the current study, there were lower mortality rates for those who consumed cheese 1 to 6 times/week. Based on the NHEFS results of the current study, and those from other studies [3843], it appears that frequent consumption of cheese may not constitute undue cardiovascular risk.
The inverse associations of legume intake with CHD event rates in the Midwest region, and in age groups 50 to 59 and 60 to 69 probably reflect the cardioprotective effects of diets rich in fruits and vegetables, rich in magnesium and in antioxidant vitamins A, C, E, and beta-carotene [44,45].
The 16 year NHEFS observational epidemiologic follow-up study emphasizes again [1,7] the important role of modifiable dietary and behavioral factors in the causation and prevention of CHD.
| ACKNOWLEDGMENTS |
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Received April 1, 1997. Accepted October 1, 1997.
| REFERENCES |
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