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Journal of the American College of Nutrition, Vol. 17, No. 5, 425-434 (1998)
Published by the American College of Nutrition

Cardiovascular Disease Risk Factors are Lower in African-American Vegans Compared to Lacto-Ovo-vegetarians

M. Lynn Toohey, PhD, Mary A. Harris, PhD, DeWitt Williams, PhD, MPH, Gwen Foster, MPH, W. Daniel Schmidt, PhD and Christopher L. Melby, DrPH

Department of Food Science and Human Nutrition (M.L.T., M.A.H., C.L.M.), Colorado State University, Ft. Collins
General Conference of the Seventh-Day Adventist Church (D.W., G.F.), Silver Spring, Maryland
University of Wisconsin-Oshkosh (D.S.), Oshkosh, Wisconsin

Address reprint requests to: Christopher L. Melby, Dr PH, Department of Food Science and Human Nutrition, 226 Gifford Building, Colorado State University, Fort Collins, CO 80523


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Objective: This study was undertaken to determine if African-American strict vegetarians (vegans) exhibit lower blood pressure (BP) and a more favorable serum lipid profile than their lacto-ovo vegetarian (LOV) counterparts, and if plasma ascorbic acid (AA) concentrations could explain any group differences in these cardiovascular disease (CVD) risk factors.

Methods: Habitual dietary intake, anthropometric characteristics, blood pressure, and blood lipids and ascorbic acid concentrations were determined in African-American study participants (male vegans, n=14, age=45.6 years; male LOV, n=49, age=49.8; female vegans, n=31, age=51.1, female LOV, n=94, age=52.1) recruited from Seventh-Day Adventist Churches in several cities in the northeastern United States.

Results: Body mass index (BMI) was significantly lower in the vegans (24.7±1.9 kg/m2) compared to LOV (26.4±0.45 kg/m2). There were no diet or gender differences in BP. Serum total cholesterol (3.75±0.12 vs. 4.51±0.10 mmol/L), LDL-cholesterol (2.06±0.13 vs. 2.65±0.09 mmol/l), and triglycerides (0.94±0.07 vs. 1.17±0.04 mmol/L) were significantly (p<0.05) lower in vegans compared to LOV, but there were no dietary group differences in HDL-C. The ratio of total to HDL-cholesterol was significantly lower in vegans than in LOV (3.0±0.13 vs. 3.7±0.13). There were no dietary group differences in plasma AA concentrations. However, in the entire sample, plasma AA was inversely associated with BP (SBP: r=-0.46, p<0.001, DBP: r=-0.32, p<0.001), but unrelated to the serum lipid concentrations.

Conclusion: African-American vegans exhibit a more favorable serum lipid profile than lacto-ovovegetarians and plasma AA is inversely related to BP in African-American vegetarians but does not explain any of the differences in CVD risk factors between vegans and lacto-ovo vegetarians.

Key words: blood pressure, blood lipids, diet, heart disease, vitamin C


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The vegetarian diet has been found to be associated with some degree of protection against hypertension [1,2] and high blood lipid levels [3–5]. However most of these studies have been conducted in Caucasians, and it remains unclear as to how much protection against hypertension and other risk factors for cardiovascular disease (CVD) is afforded by a vegetarian diet in African Americans. We reported lower average systolic blood pressure (BP) in black vegetarians compared with nonvegetarians, but higher BP than either white vegetarians or white nonvegetarians [6]. In a more recent study we found that Black Seventh-Day Adventist vegetarians had significantly lower concentrations of serum total cholesterol (STC), low-density lipoprotein cholesterol (LDL-C), triglycerides, STC/high-density lipoprotein cholesterol (HDL-C), and LDL-C/HDL-C than the nonvegetarians [7], but there were no significant group differences in BP. In this latter study we made no comparisons between strict vegetarians who consume no animal products (vegans) and the more common lacto-ovo-vegetarians.

When Caucasian vegans have been compared to lacto-ovo-vegetarians and nonvegetarians, the former have been shown to exhibit lower risk for cardiovascular disease. Phillips et al [8] reported a lower CVD mortality rate among strict vegetarian Seventh-Day Adventists compared to their lacto-ovo-vegetarians and omnivorous counterparts. McDougall et al [9] reported a rapid decrease in serum cholesterol and blood pressure when subjects were placed on a strict vegetarian diet for twelve days. However, it is not known whether African-Americans vegans exhibit a more favorable blood lipid profile in comparison to lacto-ovo-vegetarians, and whether there are blood pressure differences between African-American lacto-ovo-vegetarians and vegans. Our understanding of the specific constituents of the vegetarian diet which afford protection against CVD is limited. While it is likely that the lower intakes of cholesterol and saturated fat characteristic of a plant- compared to animal-based diet contribute to lower blood lipid concentrations in vegetarians, it is unclear what dietary factors may be related to their lower risk for hypertension. We have recently been interested in the relationships among ascorbic acid (AA), the vegetarian diet, and CVD risk, owing to studies in which either AA intake or plasma concentration was found to be inversely related to BP [10–16] and total blood cholesterol [17,18]. A few small clinical trials have suggested that AA may lower BP [19,20] as well as blood lipids [19,21]. These trials, however, have all been conducted with white subjects.

Using the same data base from the previously cited study of African-Americans [7], we found plasma AA to be inversely related to serum total and LDL-C, BP, and malondialdehyde (MDA) equivalents [22] (used to estimate the magnitude of lipid peroxidation [23]). Additionally, plasma AA concentrations were positively related to serum HDL-C in the sample. However, these findings regarding plasma AA and CVD risk factors in African-Americans await confirmation from further studies. Therefore, the purpose of this study was to examine BP and blood lipids in a sample of Black Seventh-day Adventist vegans and lacto-ovo-vegetarians. In addition, the plasma concentrations of AA and MDA equivalents were measured in an attempt to confirm our earlier findings and to determine if plasma AA concentrations could explain any differences in CVD risk factors between African-American lacto-ovo-vegetarians and vegans.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
SubjectS
The study sample was selected from three sites: Washington, DC; Philadelphia, PA; and Baltimore, MD, where black members of the Seventh-day Adventist Church were recruited to participate in the study. Church leaders were contacted in advance and the nature of the study was explained to them orally and in writing. They were specifically requested to ask all African-American vegetarians within their churches to participate. Potential subjects were requested to come to their churches on one of several pre-arranged days to complete questionnaires regarding their health history, health habits, and dietary intake and undergo measurement of anthropometric characteristics and blood pressure, and provide a sample of blood drawn for further analysis. Attendance by members in each of the three cities yielded a sample of 215 study participants. Twenty subjects were excluded from analysis, because dietary assessments revealed their consumption of small, but regular amounts of meat, fish, or poultry, and thus they were neither vegans or lacto-ovo-vegetarians. Seven additional subjects were excluded due to substantial amounts of missing data (e.g., completion of questionnaire but unwillingness to undergo other testing) leaving a sample of 188 subjects (45 vegans and 143 lacto-ovo-vegetarians). There were a few missing values for specific variables for some of the 188 subjects, which accounts for the different sample sizes reported in the tables.

Experimental Design
This study was a cross-sectional epidemiological investigation designed to examine possible blood pressure and blood lipid differences between black vegans and black lacto-ovo-vegetarians, and also to determine whether plasma AA and MDA were related to the measured CVD risk factors in the entire sample. Subjects gave their written consent to participate. The study was approved by the Human Research Committee at Colorado State University.

Dietary Assessment
Subjects completed a health habits and history questionnaire, and a food-frequency questionnaire in private (Right Byte, Nutritionist III; N-Squared Computing, Silverton, OR). The health habits and history questionnaire requested information on demographic characteristics, personal and family health history, and personal health habits. The food frequency questionnaire recorded the amount and frequency of their usual consumption of 141 different foods and related food items during the previous 3 months. Macro- and micronutrient intakes were estimated using the computer software that uses the nutrient data base of the US Department of Agriculture [24]. There is likely a small degree of underestimation in intake of several micronutrients owing to missing zinc, chromium, and vitamin D values for several food items in the nutrient data base. Specific procedures used in this study were similar to those reported from a previous study of cardiovascular disease risk factors in African-Americans, and thus only a brief summary of similar specific procedures is provided below. A more detailed description of these methods is found in Melby et al [7].

Blood Pressure Measurement
Following a 5-minute seated rest, two resting BP measurements were taken (spaced 2 minutes apart) for each subject using a standard mercury sphygmomanometer, and the average of the two BP readings was used in the statistical analyses.

Anthropometric Measurements
Height (ht) without shoes, body weight (wt) (included the weight of light indoor clothing minus shoes), body mass index (BMI) (calculated as wt (kg)/ht (m)2), and waist, hip, and thigh circumferences were measured in subjects. The waist-to-hip circumference ratio (WHR) and the waist-to-thigh circumference ratio (WTR) were determined as indices of fat patterning.

Blood Analysis
Venous blood samples were drawn into blood tubes from the antecubital space of the forearm from fasted subjects. Blood for lipid analysis was allowed to clot for 20 minutes, centrifuged for 20 minutes, and then refrigerated. Within several hours of each day’s blood draw, the tubes were placed on dry ice and immediately shipped by air to the Department of Food Science and Human Nutrition at Colorado State University. The vials were frozen at -70°C; analyses for triglycerides, total and HDL-cholesterol were determined by enzymatic assay; LDL-cholesterol was estimated using the equation method of Friedewald [25]. Because of various difficulties (e.g., non-fasting sample, failure to obtain an adequate amount of blood, etc.) blood lipid assays were available for 40 of 45 vegans and 135 of 143 lacto-ovo-vegetarians.

A second venous blood sample was drawn into a tube containing EDTA for the AA and MDA assay. Blood was centrifuged for 20 minutes, and the plasma was pipetted into separate vials for AA and MDA analysis and refrigerated. The specimens were then placed on dry ice and returned to Colorado State University, Fort Collins, CO at which time they were immediately placed in a freezer at -70°C. Plasma for the AA assay was deproteinized with trichloroacetic acid, and analyzed by the assay of Zannoni [26]. MDA (as an indicator of lipid peroxidation) was estimated by the thiobarbituric acid (TBA) test of Yagi [27], as modified by Tatum et al [28]. Peroxidation values were expressed as mmol MDA equivalents per liter (mmol/L) plasma. The TBA test is an indirect estimate of lipid peroxidation and measures MDA produced from the decomposition of peroxidized polyenoic fatty acids [22].

Data Analysis
All data analyses were performed using the Statistical Analysis Systems (SAS, Cary, NC). Descriptive statistics were computed to characterize the men and women in the sample. Gender differences were tested using ANOVA. The characteristics of the subjects were analyzed for main effects of diet and gender and any interactions using a two-way ANOVA (diet at two levels by gender at two levels). Simple correlation analyses were performed to identify associations among plasma AA, plasma MDA, and specific CVD risk factors. Stepwise multiple regression analyses were used to identify the independent variables which together explained the most variance in blood pressure and blood lipid values. Specifically, AA and MDA were included in these analyses to determine whether or not they were related to the blood lipids and BP independent of specific anthropometric and dietary characteristics. The values for all subject characteristics are reported as the mean±SEM. The probability of committing a type I error was set at p<0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The physical characteristics of the male and female subjects (divided into dietary groups) are presented in Table 1. The sample was composed of primarily middle-aged black adults (average age of the four groups was between 45 and 52 years of age). The lacto-ovo-vegetarians had been members of the Seventh-day Adventist church for a significantly longer period of time than the vegans (p<0.001). The lacto-ovo-vegetarians weighed more than the vegans (p<0.05). As would be expected, compared to females, males exhibited significantly higher measured values for waist circumference, waist:thigh ratio, and waist:hip ratio. Body mass index (BMI) did not differ between sexes; however, the vegans exhibited a lower mean BMI value than the lacto-ovo-vegetarians. The vegans also exhibited significantly lower measurement values for thigh circumference and waist:hip ratio compared to the lacto-ovo-vegetarians. Additionally, there was a diet by sex interaction for waist:hip ratio measurements, with male lacto-ovo-vegetarians having higher values than either of the other three groups.


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  		Table 1. Characteristics of the Male and Female Dietary Groups of Black Adults12

 
The nutrient intake data of the male and female dietary groups are shown in Table 2 (macronutrients) and Table 3 (micronutrients). For both the macro- and micronutrients, data are expressed on an absolute basis and in amounts relative to energy intake. The vegans consumed significantly more carbohydrates, less total and saturated fat, and less cholesterol than the lacto-ovo-vegetarians. Vegans also had a significantly higher fiber intake relative to energy intake, and a higher ratio of polyunsaturated fatty acids to saturated fatty acids (P:S ratio).


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  		Table 2. Macronutrient Intake of Male and Female Vegans and Lacto-Ovo-vegetarians12

 

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  		Table 3. Micronutrient Intake of Black Male and Female Vegans and Lacto-ovo-vegetarians12

 
There were numerous dietary group differences in the intake of micronutrients. The average estimated daily intake of AA was greater than the Recommended Daily Amount (RDA) (60 mg/day) for both dietary groups, however, the vegans had a significantly higher intake, than the lacto-ovo-vegetarians. After standardizing for energy intake, vegans had higher intakes of vitamin A, alpha-tocopherol, thiamin, vitamin B6, folate, potassium, magnesium, iron, zinc, and chromium. Vegans consumed less sodium, vitamin D, vitamin B12, and calcium.

The unadjusted group means for blood pressure, blood lipids, the plasma levels of AA and MDA equivalents are presented in Table 4. The mean BP values were in the normotensive range for all groups and there were no systolic or diastolic BP differences between vegans and lacto-ovo-vegetarians. The blood lipid values were quite low for all four groups, with vegans exhibiting significantly lower concentrations of STC, LDL-C, triglycerides, and serum total cholesterol:HDL-cholesterol (STC:HDL-C). For HDL-C, there was a main effect of gender, with females exhibiting higher mean values than males. There were no gender or diet differences in plasma AA or MDA equivalents. Table 5 shows values of the blood lipid means adjusted for age and waist-to-hip ratio. While the group differences were attenuated somewhat, the differences remained significant. The blood lipid differences between vegans and lacto-ovo-vegetarians were similar when BMI was used as a covariate (not shown in table format).


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  		Table 4. Unadjusted Blood Pressure, Plasma Lipids, Ascorbic Acid, and Malondialdehyde Equivalents in African-Americans Characterized by Diet and Gender12

 

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  		Table 5. Blood Lipids Adjusted for Age and Waist-to-Thigh Circumference Ratio in Black Americans by Diet and Gender12

 
The simple correlations among plasma AA, MDA equivalents, blood lipids, BP, and several anthropometric characteristics are reported in Table 6. There were significant inverse correlations between plasma AA levels and both systolic and diastolic BP. The correlation for MDA and BP was of similar magnitude to that of plasma AA, but was in the opposite direction. Age was the variable most strongly correlated with BP, both systolic and diastolic. Various indices of fat patterning were typically correlated with CVD risk factors at least as strongly as was body mass index. The dietary P:S ratio was correlated (inversely) with STC and LDL-C.


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  		Table 6. Correlation (Pearson’s r) of Selected Subject Characteristics With Cardiovascular Risk Factors in African-Americans12

 
The data were analyzed using step-wise multiple regression analysis to determine the subset of variables which as a group contributed to explaining the most variability in blood pressure and blood lipids (Table 7). Variables used in the multiple regression analyses were those identified to be significantly correlated to BP and blood lipids in the simple correlational analyses. These analyses allowed us to determine if plasma AA and MDA concentrations were predictors of BP independent of other correlates established from the simple correlation analyses [age, anthropometric characteristics including BMI, waist circumference and WHR, hip circumference and WHR, and the ratio P:S. Variables significantly associated with BP and the blood lipids in the simple correlational analyses were initially entered into the multiple regression models, but only variables meeting the p<0.10 level of significance as independent contributors remained in the models.


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  		Table 7. Best Predictors of Blood Pressure in Black Adults as Determined by Multiple Regression Analysis1

 
The variables age, AA, and MDA together explained 53% of the variability in SBP for the entire sample, with age accounting for most of the variability, followed by AA and MDA as independent predictors. Only 16% of the variability in DBP could be explained in the multiple regression model. Plasma AA emerged as the greatest independent predictor, followed by protein (% energy) and waist circumference.

The multiple regression analyses (not shown in table format) revealed that age and anthropometric measures (i.e., BMI, waist circumference, WHR) were the best predictors of the blood lipids. Dietary fiber was inversely related to several blood lipid variables and emerged as a significant independent contributor to the prediction of triglycerides, and the ratios STC:HDL-C and LDL-C:HDL-C. Neither MDA nor AA were independently related to any of the blood lipid concentrations.

The entire sample of subjects, regardless of gender and dietary group, was divided into tertiles based on plasma AA concentrations (Tertile 1: mean AA=66.4 µmol/L; Tertile 2: mean AA=90.8 µmol/L; Tertile 3: mean AA=141.9 µmol/L). The mean systolic and diastolic BPs were significantly lower for the highest plasma AA tertile (mean BP=119.5/76.6 mm Hg) compared to the lowest plasma AA tertile (mean BP=139.5/82.6 mm Hg). These upper and lower tertile differences in BP remained statistically significant, even after adjusting the BP means using age and gender as covariates (adjusted blood pressure for highest plasma AA tertile: 121.5/77.0 mm Hg versus adjusted BP for lowest plasma AA tertile: 135.1/82.1 mm Hg).

Because both plasma AA and MDA concentrations were related to blood pressure, we compared these variables in those individuals with confirmed physician-diagnosed HT (based on the use of antihypertensive drugs) and normotensive subjects. Plasma AA was significantly lower (p<0.0001) for those with hypertension (n=32, 52.2±7.9 µmol/L) compared to those with normal blood pressure (n=156, 96.0±4.0 µmol/L). Plasma MDA levels were significantly higher (p<0.007) for hypertensive subjects (1.16±0.03 mmol/L) compared to normotensive subjects (1.08±0.01 mmol/L).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
A major finding of this study is that among black adults, self-reported vegans exhibited a more favorable lipid profile in comparison to lacto-ovo-vegetarians. This study also corroborated our earlier findings that among African-American Seventh-Day Adventists, both SBP and DBP were inversely correlated with plasma AA, and positively correlated with MDA equivalents, a nonspecific marker of lipid peroxidation. It is not known if these associations would be characteristic of other African-American populations.

Vegetarian Diet, BP and Cholesterol
In the present study, there were no blood pressure differences between vegans and lacto-ovo-vegetarians. In an earlier study, black vegetarians exhibited lower BP than black nonvegetarians [6]; however, in a follow-up study, we found no significant BP differences among vegetarians, semi-vegetarians, and nonvegetarians, possibly due to lack of adequate dietary differences between groups. However, in this previous study, the prevalence of treated hypertension was significantly higher among the nonvegetarians compared to the vegetarians. The disproportionately higher percentage of nonvegetarians using pharmacologic therapy to lower BP would clearly attenuate the true blood pressure differences between groups. The reason for the lack of group blood pressure differences in the current study is not clear. There were no dietary group differences in the prevalence of pharmacologically-treated hypertension. Note, that the prevalence of hypertension in the sample was low, with only 17% of the subjects (32 of the 188 subjects) being treated for hypertension. It would appear that adherence to a vegan diet is not associated with a greater protective effect against untoward blood pressure elevation than a lacto-ovo-vegetarian diet. Although there were some significant differences in macronutrients (vegans ingested more carbohydrates and dietary fiber, ingested less total fat, saturated fat, and cholesterol, and had a higher dietary P:S ratio than lacto-ovo-vegetarians), these dietary differences did not result in BP differences between groups. The small sample of vegans in this study, especially males, may have limited the possibility of identifying group blood pressure differences.

While the group differences in the aforementioned dietary macronutrients were not related to BP, these dietary differences may have contributed to the more favorable lipid profile of the vegans compared with lacto-ovo-vegetarians. The dietary P:S ratio was significantly and inversely related to many of the lipid values, such as STC, LDL-C, and the ratios STC/HDL-C and LDL-C/HDL-C. Saturated fatty acids are known to raise STC while polyunsaturated fatty acids are known to decrease STC [29]. The higher intake of dietary fiber among the vegans may also have contributed to their more favorable lipid profiles, given the significant inverse correlation of fiber with the lipid variables STC, LDL-C, and the ratios STC:HDL-C and LDL-C:HDL-C. The vegans exhibited significantly lower values for several anthropometric characteristics associated with blood lipid levels. However, it is apparent that the lower values for the aforementioned blood lipids among vegans cannot solely be explained by their lower body weight, BMI, and waist:hip values, as the group lipid differences remained significant even after using the anthropometric characteristics as covariates in the statistical analysis. Note, there was a small intake of cholesterol reported for vegans, and their average intake of vitamin B12 was higher than expected for individuals who ingest no animal foods. These phenomena appear to be related to the inability of the nutrition analysis software to distinguish between home-prepared foods which contained no eggs versus commercially prepared products with eggs (e.g., vegans use of homemade mayonnaise and baked goods without eggs versus the commercially prepared products which were in the nutrition data base).

Plasma AA, MDA Equivalents and Blood Pressure
Because of our previous observations that concentrations of plasma AA and MDA equivalents were related to CVD risk factors in Black Americans, we measured these blood constituents in order to possibly help explain any blood pressure and blood lipid differences between vegans and lacto-ovo-vegetarians. In a recent study, the plasma AA concentrations of vegans compared to omnivores was significantly higher [30]. However, in our study, despite the higher intake of AA among the vegans, there were no significant group differences in plasma AA, nor was AA intake related to plasma AA (r=0.03, p=0.72). The lack of an association between dietary AA and plasma AA concentrations is not unusual, given that the association between the two is often weak [20], and the response curve of plasma AA to AA intake levels off at intakes below the mean intake for both dietary groups in this study. We attempted to measure the amount of supplemental AA taken by the study subjects. However, most subjects taking supplements were unable to recall whether or not the supplement included AA, or the mg of AA provided from supplemental use. The 35 subjects who reported using AA supplements (ranging from daily to only occasional use) exhibited mean plasma AA concentrations (87.9±5.7 µmol/L) that were no different than nonsupplementers (88.2±4.2 µmol/L). Unfortunately, the lack of accurate data on AA supplementation precludes drawing any conclusions regarding the relationships among supplemental intake, plasma AA concentrations, and BP.

Despite lack of dietary group differences in plasma AA and blood pressure, we examined the relationships among CVD risk factors and plasma AA and MDA concentrations in the entire sample. Both SBP and DBP were inversely correlated with plasma AA, and positively correlated with MDA equivalents, a nonspecific marker of lipid peroxidation. In a previous study [23], we reported a significant inverse relationship between plasma AA and BP, and a positive relationship between MDA and BP. The current study supports these earlier findings, as AA and MDA were not only related to BP (inversely and positively, respectively), but AA emerged as an independent predictor in the multiple regression analysis.

Due to the observational nature of the current study, it is not possible to infer causality between AA and BP. The relationship could be a coincidental association due to confounding by subject characteristics related to both AA and BP. Plasma AA may only serve as a marker for other factors causally related to BP, such as higher intake of fresh fruits and vegetables, which are rich in magnesium, potassium, and a variety of phytochemicals. However, it is interesting that the multiple regression analysis showed AA to be a significant predictor of both SBP and DBP, independent of age and any of the well known anthropometric correlates of BP. Also, because this study included only Seventh-Day Adventists who do not imbibe alcohol or use tobacco products, this association was independent of any confounding due to these habits. It is not known if these associations would be characteristic of other African-American populations.

One must consider the possibility that elevated blood pressure produces physiologic changes that lower plasma AA concentrations. Those with physician-diagnosed hypertension had significantly lower plasma AA and higher plasma MDA concentrations compared to subjects who were normotensive. However, it should be noted that several clinical trials have suggested that AA supplementation can potentially lower BP [19,20,31]. None of these clinical trials, however, have tested the BP-lowering effect of AA in African-Americans.

There are several possible mechanisms by which AA could theoretically influence BP. Because AA scavenges free radicals which inhibit prostacyclin (PGI2) synthesis, a potent vasodilator [20], lower AA concentrations could result in higher vasomotor tone leading to higher BP [12,14]. Ascorbic acid has been shown to attenuate smoking-induced increases in BP that were attributed to the production of free radicals [32]. Additionally, the superoxide radical interferes with the vasodilator nitric oxide, can increase endothelin production, (a potent vasoconstrictor), and is thought to have possible vasoconstrictive properties of its own [33]. Ceriello et al [34] proposed that antioxidants might have an indirect dilatory effect and that an imbalance of free radicals to nitric oxide might facilitate the development of HT in humans.

It is also possible that AA may affect BP by way of its protection of cell membrane ion pumps from damage due to oxygen free radicals [35]. Black Americans are known to exhibit salt-sensitive HT with increased frequency when compared to their white counterparts and demonstrate altered activities in sodium ion pumps, including Na+K+ ATPase, Na+H+ exchange, and Na+ Li+ countertransport [36]. In one trial, Koh et al [19] reported that AA supplementation significantly lowered sodium levels; they postulated that the variable effect of plasma AA on BP in the study sample might be explained by subject differences in salt-sensitivity for HT.

We also found a significant correlation between BP and MDA. In previous reports, MDA has been found to be positively associated with BP [33,37]. However, to our knowledge this relationship has not been examined in the black population with the exception of our previous study [23]. Again this association may be coincidental, with MDA serving only as a marker for other factors causally related to BP. Given that MDA is an indicator of lipid peroxidation caused from free radical production, it may be that MDA, AA and BP are related by way of the antioxidant status of the subjects as discussed above.

Blood lipid differences, plasma AA levels and MDA equivalents might possibly be influenced by antihypertensive medication in some subjects. As discussed previously, in the present study, medically-treated hypertensive subjects exhibited significantly lower plasma AA concentrations and higher MDA concentrations than their normotensive counterparts. However, even when the data were analyzed with the exclusion of those on BP medication, the associations of AA and MDA with blood pressure remained significant.

In conclusion, Seventh-Day Adventist African-American vegans compared to lacto-ovo-vegetarians, exhibited significantly higher intakes of nutrients which are associated with reduced risk for CVD, including fiber, AA, alpha-tocopherol, potassium, magnesium, vitamin B6, and folate, and lower intakes of sodium. They also ingested less total and saturated fat and exhibited lower levels of several lipid parameters, including STC, LDL-C, triglycerides, and STC:HDL-C. While there were no blood pressure differences between dietary groups, both SBP and DBP were inversely correlated with plasma AA and positively correlated with MDA equivalents within the entire sample. Future research should examine the possibility that a plant-based diet not only improves the lipid profile in African-Americans, but also reduces their risk of CVD.


   ACKNOWLEDGMENTS
 
This study was supported by a Faculty Research Grant, Colorado State University and by the Colorado Agricultural Experiment Station, Project #616 (CLM). The authors would like to thank the General Conference of Seventh-Day Adventists and the Allegheny East Conference of Seventh-Day Adventists for their cooperation in conducting this study. Special thanks to Lester Ortiz, Dr. Geneva Jackson, Barbara Finnestead and Caleb Melby for their help in collecting and processing the data, and to Dr. Albert Sanchez for his editorial comments. Finally, we would like to thank the study participants for their cooperation.


   FOOTNOTES
 
Send page proofs to: Dr. Christopher L. Melby, Department of Food Science and Human Nutrition, 226 Gifford Building, Colorado State University, Fort Collins, Colorado 80523.

Received January 1, 1998. Accepted April 1, 1998.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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