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Journal of the American College of Nutrition, Vol. 19, No. 5, 622-627 (2000)
Published by the American College of Nutrition

Original Research

Vegetarianism and Ischemic Heart Disease in Older Chinese Women

Timothy Kwok, MB, ChB, Jean Woo, MD, Suzanne Ho, PhD, MPH and Aprille Sham, MBA

Department of Medicine & Therapeutics (T.K., J.W.), The Chinese University of Hong Kong, Hong Kong, CHINA
Department of Family & Community Medicine (S.H., A.S.), The Chinese University of Hong Kong, Hong Kong, CHINA

Address reprint requests to: Dr. Timothy Kwok, Department of Medicine & Therapeutics, Prince of Wales Hospital, Shatin, Hong Kong, CHINA. E-mail: TKWOK{at}UHK.EDU.HK


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Objective: This study compared the risk of ischemic heart disease among older vegetarian Chinese women with that of older non-vegetarian women.

Methods: 90 vegetarian Chinese women over 70 years old in Hong Kong were screened for ischemic heart disease by electrocardiogram (ECG) and cardiovascular questionnaire. They were compared with 90 non-vegetarian women of similar age examined in a previous local survey. The effects of confounding factors were adjusted by stepwise logistic regression analysis.

Results: The percentages of subjects with ischemic heart disease defined by symptoms and ECG or by ECG alone were significantly lower in vegetarian women (p <0.005 and p<0.05 respectively). Vegetarians had lower serum cholesterol levels; more were old age home residents and were less likely to perform regular exercise. On stepwise logistic regression, using probable ischemic heart disease defined by questionnaire and ECG as outcome measure, vegetarianism was the only significant predictor (OR 0.3, 95%CI 0.1–0.6, p<0.005).

Conclusions: Vegetarian older Chinese women had lower risk of ischemic heart disease when compared with non-vegetarians. Apart from lower serum cholesterol levels, vegetarianism may have other protective factors against ischemic heart disease.

Key words: coronary disease, vegetarianism, diet, aged, elderly


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Vegetarians have been shown to have lower mortality from ischemic heart disease (IHD) in epidemiological studies [1,2]. The benefit is attributed to a more favorable lipid profile [3]. In addition, the vegetarian subjects in Western studies tended to be health conscious, non-smokers and middle class. Moreover, the reduction in cardiovascular mortality associated with a vegetarian diet in women and in older people had been less significant or not demonstrable [2,4].

In Hong Kong, there is a minority group of older Chinese people, predominantly female, who have been life long vegetarians for religious reasons (Taoism and Buddhism). The women led a subsistent communal life either in temples or in private lodgings, performing as light manual workers before retirement. This study compared the risk of ischemic heart disease among this group of older vegetarian women with that of community dwelling older non-vegetarian women in Hong Kong. The effects of confounding factors were adjusted by stepwise logistic regression analysis.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Chinese women above 70 years old and who had been vegetarian for more than ten years were recruited from two sources in Hong Kong: a Taoist old age hostel and its associated members in the community, and two Buddhist old age homes. Taoists were vegans and Buddhists were lacto vegetarians. All subjects had to be self-ambulatory and be able to attend Prince of Wales Hospital, a teaching hospital, on their own accord. The research protocol was approved by the Human Research Ethics Committee of the Chinese University of Hong Kong. Written informed consent was obtained from all subjects.

Sections A and B of the London School of Hygiene Cardiovascular Questionnaire [5] translated into Chinese were administered. The same criteria for angina and possible infarction were used. Information was also obtained on past history of ischemic heart disease, diabetes mellitus, hypertension, current medication, smoking habits, use of alcohol and types and frequency of physical exercise. Cognitive function was as-sessed by the information/orientation section of the Clifton assessment procedure for the elderly. Subjects with scores below the cut-off point of seven for dementia were excluded because they might not give reliable answers to the cardiovascular questionnaire, and none of the historical control subjects were judged to have dementia.

A resting electrocardiograph (ECG) was performed by a trained nurse and read by a physician (TK). The Minnesota Coding [6] was used to classify ECG. The Whitehall Criteria [7] were used to classify the ECG into probable (codes 11,1.2) or possible (codes 1.3, 4.1–4.4, 5.1–5.3, 7.1) ischemic heart disease. Using the cardiovascular questionnaire, ECG findings and past history, subjects were classified as having probable (positive symptoms, documented history of disease and current medication or ECG showing probable disease), possible (no history or symptoms but ECG showing possible disease) or no (not falling into the above two categories) ischemic heart disease. Fasting blood was taken for serum cholesterol and triglyceride levels, and body weight and height were measured to calculate body mass index. To assess their dietary intake, 24-hour dietary recall was performed.

The non-vegetarian women consisted of 90 community dwelling Chinese above 70 years old. They were part of a large-scale community survey of older Hong Kong Chinese people recruited by stratified random sampling [8]. These control subjects were a subset of people who volunteered to attend Prince of Wales Hospital for electrocardiogram [9]. They had the same measurements as the vegetarian subjects. Their dietary habit was assessed by food frequency questionnaire. Those found not to consume any meat regularly were excluded.

Vegetarians and non-vegetarians were compared by chi-square test for nominal data, and by Student’s t test for continuous data. The associations of vegetarianism and other potential confounders with ischemic heart disease were investigated by univariate logistic regression in the first instance. Those variables with p values<0.25 were then subjected to stepwise logistic regression analysis.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
One hundred vegetarian women participated, but ten subjects were excluded because subnormal mental scores. Fifty-three of them (58.9%) were vegans, and the rest were lacto vegetarians. The average duration of vegetarianism was 41.1 (SD 17.2) years. The characteristics of vegetarians and non-vegetarians are compared in Table 1. The dietary practice of the non-vegetarians as assessed by food frequency questionnaire is shown in Table 2. Twenty-four hour dietary recall instead of food frequency questionnaire was performed in the vegetarian subjects. According to the recall, the percentages of vegetarian subjects consuming the various food categories were as follows: red/white meat, liver, fish 0 %; green/non-green leafy vegetables, fruit, soy bean products 100%; milk 62.4%; egg 4.4%.


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  		Table 1. The characteristics of vegetarian and non-vegetarian older chinese women

 

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  		Table 2. Food frequency of non-vegetarian women

 
The percentages of subjects with cardiac symptoms and ischemic heart disease in both groups are compared in Table 3. Three vegetarian subjects refused ECG. Two of them reported history of ischemic heart disease with medication and were therefore classified as having probable ischemic heart disease. The remaining one had no cardiac history or symptoms, but her ischemic heart status could not be classified. Another three vegetarians’ serum lipid levels were missing. They were therefore not included in logistic regression analysis.


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  		Table 3. Cardiac symptoms and disease in vegetarian and non-vegetarian older chinese women

 
The age adjusted odd ratios of all the potential predictors of ischemic heart disease on univariate logistic regression analysis are shown in Table 4. Age had a significant association with IHD. An age of 80 years or more when compared with 70 to 79 years had odds ratios of 0.5 (0.2–1.0) and 0.5 (0.3–1.0) for probable and possible/probable ischemic heart disease, respectively. In addition to age, the variables that were entered into stepwise logistic regression are shown in Table 4.


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  		Table 4. The odds ratios of predictors of ischemic heart disease (IHD)#

 
On stepwise logistic regression, the only significant predictors of probable ischemic heart disease were vegetarianism (OR 0.3, 95%CI 0.1–0.6, p<0.005). Serum triglyceride level was close to being included into the final regression model (OR 2.1, 95%CI 0.9–4.7, p<0.07). For possible or probable disease, the only significant predictor was history of hypertension (OR 2.6, 95%CI 1.3–5.1, p<0.005). There was an insufficient number of subjects with cardiac symptoms or probable ischemic changes on ECG for multivariate logistic regression.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This study showed that older vegetarian women had a lower risk of ischemic heart disease when compared with their omnivorous counterparts. The protective effect was independent of other risk factors of ischemic heart disease.

All the vegetarian subjects have adopted the vegetarian diet for more than ten years, most starting at young age. Dietary compliance was expected to be extremely good because of communal living in a religious environment. They were different from the vegetarian subjects in Western studies in that they were in advanced age, had a working class background and were not especially health conscious. The food items mentioned in their 24-hour dietary recall were consistent with a vegetarian diet. More detailed assessment of their dietary intake (24-hour recall method) and nutritional status was reported elsewhere [10]. The main finding was that the intakes of energy, fat, protein calorie, thiamine, riboflavin and niacin were significantly lower in vegetarians when compared with omnivorous women of similar age. Fifty four percent of the vegetarian women had serum vitamin B12 levels below 150 pmol/L, thus indirectly confirming their compliance to their vegetarian practice.

The control subjects were part of a community survey conducted in Hong Kong a few years ago [9]. They were representative of older people in Hong Kong in that they were recruited by random sampling in the community, except that the frail elderly and old age home residents were not included. Their proportion of subjects with ischemic heart disease was similar to those reported in studies of older Caucasians [9,11].

The vegetarian and non-vegetarian subjects were comparable in age and body mass index. They were also comparable in the percentages of self-reported diabetes mellitus and hypertension, which were consistent with the local norm [8]. However, it is likely that diabetes mellitus was under-diagnosed in both groups as the prevalence, defined by fasting serum glucose concentration, among local Chinese people above 75 years old was reported to be 17.1% [12]. Although more than half of the vegetarians were recruited from old age homes and none of non-vegetarians was an old age home resident, all the vegetarian old age home subjects were self-ambulatory. Furthermore, vegetarian old age home residents did not differ from community dwelling vegetarians in percentages with disease defined either by ECG alone or in combination with questionnaire (data not shown).

As in other studies [13,14], vegetarians had significantly lower serum cholesterol levels. This could be attributed to their low fat intake [15]. But their high dietary intake of soy bean products, as demonstrated in the 24-hour dietary recall, could also have a cholesterol lowering effect [10,16]. It was somewhat surprising that vegetarians were less physically active than non-vegetarians. The difference could not be attributed to institutionalisation, as a greater proportion of old age home residents exercised daily than community dwelling subjects (30.9 % vs. 17.1%, p=0.22, chi-square test). This was consistent with our assertion that this group of vegetarians was not particularly health conscious.

The WHO cardiovascular questionnaire has been found to be 79% in sensitivity and 98% in specificity in a survey of older people [17]. The sensitivity is expected to increase when the questionnaire is combined with ECG appearance and medical history [9]. However, only a minority of subjects reported cardiac chest pain, as silent coronary ischemia is common in old age [18], and the sedentary lifestyle may protect older people from the symptom of angina. Although 15% to 20% of the subjects were diagnosed to have ischemic heart disease in the past, few of them had significant ECG changes, especially so in vegetarians.

Vegetarians had lower chance of having probable ischemic heart disease either defined by ECG alone or in conjunction with symptoms and past history. But when possible IHD cases were included in the analysis, there was no significant difference between vegetarians and non-vegetarians, because many vegetarians had non-specific T wave changes. The significance of non-specific ECG changes in older people is controversial [19–21]. Hypertension is likely to have an important role in these changes, as it was the only independent predictor of possible/probable IHD on multivariate logistic regression. Its effect could be mediated through left ventricular hypertrophy, but only three of these subjects with these changes had co-existing evidence of left ventricular hypertrophy on ECG.

Vegetarianism was an independent protective factor of probable ischemic heart disease defined by questionnaire, history and ECG. Apart from the more favorable known cardiovascular risk profile, there might therefore be additional protective factors associated with vegetarianism. It has been suggested that an active religious lifestyle might protect against IHD, but this has not yet been proven [22].

It is more likely that there are additional dietary factors that protect against ischemic heart disease [23,24]. Antioxidants, e.g., vitamin E, beta carotene and vitamin C, may render LDL particles less atherogenic [25,26]; n-3 and n-6 polyunsaturated fatty acids may reduce platelet aggregation [24]; dietary arginine abundant in certain vegetarian food (e.g., nuts) may have a positive influence on endothelial functions [27].

There has been recent interest in the association between hyperhomocysteinemia and ischemic heart disease [28]. This may be caused by genetic predisposition [29], but it can be caused by folate deficiency or more indirectly by cobalamin deficiency [30]. Vegetarian diet has high folate content, which suppresses serum homocysteine levels. On the other hand, over half of this group of vegetarians had vitamin B12 deficiency [10]. The overall effect of the combination of vitamin B12 deficiency and high folate intake in vegetarians on serum homocysteine level has not been investigated.

The association of serum triglyceride level but not cholesterol level with probable ischemic heart disease on univariate logistic regression analysis is interesting, even though it was just excluded from the stepwise logistic regression model. The association between total cholesterol and ischemic heart disease has been inconsistent [31,32]. However, an association between total cholesterol and ischemic heart disease seems to exist when the level of frailty of older people is adjusted for [33]. Triglyceride level is increasingly recognised to be an independent predictor of ischemic heart disease [34,35]. However, the apparent association observed in this study could be mediated through diabetes mellitus that has not been fully adjusted for because of underdiagnosis.

We concluded that older Chinese vegetarian women had lower risk of ischemic heart disease when compared with their non-vegetarian counterparts. This could not be attributed to the lower serum cholesterol levels of vegetarians, as serum cholesterol level was not associated with ischemic heart disease in this study. The vegetarian diet may therefore contain other protective factors against the development of ischemic heart disease.


   ACKNOWLEDGMENTS
 
We are grateful for the statistical advice by Miss Ashley Yu, Centre for Clinical Trials and Epidemiological Research, the Chinese University of Hong Kong

Received November 11, 1999. Accepted July 10, 2000.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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