Mortality In British Vegetarians: Review And Preliminary Results From Epic- Oxford1’2’3’4

Abstract

Background: Three prospective studies have examined the mortality of vegetarians in Britain. Objective: We describe these 3 studies and present preliminary results on mortality from the European Prospective Investigation into Cancer and Nutrition-Oxford (EPIC-Oxford). Design: The Health Food Shoppers Study and the Oxford Vegetarian Study were established in the 1970s and 1980s, respectively; each included about 11 000 subjects and used a short questionnaire on diet and lifestyle. EPIC-Oxford was established in the 1990s and includes about 56 000 subjects who completed detailed food frequency questionnaires. Mortality in all 3 studies was followed though the National Health Service Central Register. Results: Overall, the death rates of all the subjects in all 3 studies are much lower than average for the United Kingdom. Standardized mortality ratios (95% CIs) for all subjects were 59% (57%, 61%) in the Health Food Shoppers Study, 52% (49%, 56%) in the Oxford Vegetarian Study, and 39% (37%, 42%) in EPIC-Oxford. Comparing vegetarians with nonvegetarians within each cohort, the death rate ratios (DRRs), adjusted for age, sex and smoking, were 1.03 (0.95, 1.13) in the Health Food Shoppers Study, 1.01 (0.89, 1.14) in the Oxford Vegetarian Study, and 1.05 (0.86, 1.27) in EPIC-Oxford. DRRs for ischemic heart disease in vegetarians compared with nonvegetarians were 0.85 (0.71, 1.01) in the Health Food Shoppers Study, 0.86 (0.67, 1.12) in the Oxford Vegetarian Study, and 0.75 (0.41, 1.37) in EPIC-Oxford. Conclusions: The mortality of both the vegetarians and the nonvegetarians in these studies is low compared with national rates. Within the studies, mortality for major causes of death was not significantly different between vegetarians and nonvegetarians, but the nonsignificant reduction in mortality from ischemic heart disease among vegetarians was compatible with the significant reduction previously reported in a pooled analysis of mortality in Western vegetarians.

Generated Summary

This research article presents a review and preliminary results from the EPIC-Oxford study, focusing on mortality rates among British vegetarians. The study employs a prospective design, examining the mortality of vegetarians in Britain through three prospective studies: the Health Food Shoppers Study, the Oxford Vegetarian Study, and the EPIC-Oxford. The Health Food Shoppers Study and the Oxford Vegetarian Study were established in the 1970s and 1980s, respectively, with each including approximately 11,000 subjects. EPIC-Oxford was established in the 1990s and includes around 56,000 subjects. The methodology involves detailed food frequency questionnaires and the monitoring of mortality through the National Health Service Central Register. The researchers compared the mortality rates of vegetarians and non-vegetarians, analyzing death rate ratios (DRRs) adjusted for age, sex, and smoking. The primary objective is to describe these three studies and present preliminary results on mortality, providing insights into the health outcomes associated with vegetarian diets. The studies also analyze the mortality rates in relation to smoking, BMI, alcohol consumption, and vegetarian diet. The data presented provides valuable insights into the health outcomes associated with vegetarian diets and the influence of other lifestyle factors.

Key Findings & Statistics

• The overall death rates of all subjects in all 3 studies are much lower than average for the United Kingdom.
• Standardized mortality ratios (95% CIs) for all subjects were 59% (57%, 61%) in the Health Food Shoppers Study, 52% (49%, 56%) in the Oxford Vegetarian Study, and 39% (37%, 42%) in EPIC-Oxford.
• Comparing vegetarians with nonvegetarians within each cohort, the death rate ratios (DRRs), adjusted for age, sex, and smoking, were 1.03 (0.95, 1.13) in the Health Food Shoppers Study, 1.01 (0.89, 1.14) in the Oxford Vegetarian Study, and 1.05 (0.86, 1.27) in EPIC-Oxford.
• DRRs for ischemic heart disease in vegetarians compared with nonvegetarians were 0.85 (0.71, 1.01) in the Health Food Shoppers Study, 0.86 (0.67, 1.12) in the Oxford Vegetarian Study, and 0.75 (0.41, 1.37) in EPIC-Oxford.
• In the Health Food Shoppers Study, the SMR for all causes of death was 59% (95% CI, 57%, 61%).
• In the Oxford Vegetarian Study, the SMR for all causes of death for the whole cohort was 52% (49%, 56%).
• In EPIC-Oxford, the SMR for all causes of death for the whole cohort was 39% (37%, 42%).
• The SMRs for vegetarians and nonvegetarians for all causes of death in the Health Food Shoppers Study were 59% (55%, 63%) and 59% (56%, 62%), respectively.
• The SMRs for vegetarians and nonvegetarians for all causes of death in the Oxford Vegetarian Study were 51% (47%, 56%) and 54% (49%, 58%), respectively.
• The SMRs for all-cause mortality in nonvegetarians and vegetarians were 39% (36%, 42%) and 40% (35%, 45%) respectively in EPIC-Oxford.
• In the Health Food Shoppers Study, the DRR for all-cause mortality in vegetarians compared with nonvegetarians was 1.03 (0.95, 1.13).
• In the Oxford Vegetarian Study, the DRR for all-cause mortality in vegetarians compared with nonvegetarians was 1.01 (0.89, 1.14).
• In EPIC-Oxford, the DRR for all-cause mortality was 1.05 (0.86, 1.27).
• In the Health Food Shoppers Study, the DRR for IHD in vegetarians compared with nonvegetarians was 0.85 (0.71, 1.01).
• In the Oxford Vegetarian Study, the DRR for IHD in vegetarians compared with nonvegetarians was 0.86 (0.67, 1.12).
• In EPIC-Oxford, the DRR for IHD in vegetarians compared with nonvegetarians was 0.75 (0.41, 1.37).
• Mortality rates did not differ significantly between vegetarians and nonvegetarians.
• Vegetarians had higher mortality from all malignant neoplasms [DRR = 1.11 (0.82, 1.51)], cerebrovascular disease [DRR = 1.13 (0.65, 1.96)], and all other causes [DRR = 1.10 (0.77, 1.58)] and reduced mortality from all circulatory diseases [DRR = 0.93 (0.65, 1.32)] and IHD [DRR = 0.75 (0.41, 1.37)].
• All-cause mortality was not significantly different between vegetarians and nonvegetarians [DRR = 1.05 (0.86, 1.27)].
• Smoking increased the mortality rates for each of the cause of death categories examined; heavy smokers had DRRs of 4.13 (2.54, 6.70) for all malignant neoplasms, 4.10 (2.09, 8.02) for circulatory diseases, and 3.37 (2.37, 4.78) for all causes.
• Compared with the reference group of subjects with a BMI of 20.0-22.5, subjects with a BMI of < 20 had an increased mortality from all malignant neoplasms, circulatory diseases, all other causes, and all causes combined, although none of these increases was statistically significant.
• Compared with the reference category of subjects who reported consuming 1-7 g of alcohol per day, those in the highest category of consumption (≥ 16 g/d) had a nonsignificant lower all-cause mortality [DRR = 0.84 (0.64, 1.10)].

Other Important Findings

• The mortality of both the vegetarians and the nonvegetarians in these studies is low compared with national rates.
• Within the studies, mortality for major causes of death was not significantly different between vegetarians and nonvegetarians.
• The nonsignificant reduction in mortality from ischemic heart disease among vegetarians was compatible with the significant reduction previously reported in a pooled analysis of mortality in Western vegetarians.
• Vegetarians had a significantly increased mortality from breast cancer in the Health Food Shoppers Study and a significantly increased mortality from mental and neurological diseases in the Oxford Vegetarian Study, but these differences were not observed in the other study.
• Comparisons within the cohorts suggest that the vegetarians have a moderately lower mortality from IHD than the nonvegetarians but that there is little difference in mortality from other major causes of death.

Limitations Noted in the Document

• The numbers of deaths from individual causes are relatively small, therefore, potentially important differences might not be detected because of lack of statistical power.
• The low SMRs in the cohorts may be partly due to factors such as the low prevalence of smoking and partly due to the fact that people who are already ill and therefore likely to die within a few years are much less likely to join this type of study than are people who are healthy (the well-known “healthy volunteer effect”).
• For some participants only a short questionnaire was completed in EPIC-Oxford, and the analyses presented here are based on participants aged 20-89 y at recruitment with known smoking characteristics and diet group for whom complete questionnaire data and follow-up were available at the time of writing.
• In all 3 studies, it should be noted that the numbers of deaths from individual causes are relatively small; therefore, potentially important differences might not be detected because of lack of statistical power.

Conclusion

The study concludes that both vegetarians and non-vegetarians in these British cohort studies exhibit lower mortality rates compared to national averages. While there are few significant differences in mortality between vegetarians and non-vegetarians within these cohorts, the vegetarians showed a moderately lower mortality rate from ischemic heart disease (IHD). It is also important to note the overall health of the participants, as indicated by their lower smoking rates and lower prevalence of obesity, suggesting a “healthy volunteer effect” that may influence the findings. The low standardized mortality ratios (SMRs) across all studies support this observation. The authors emphasize that the low numbers of deaths from individual causes within each study may limit the statistical power to detect significant differences. The study’s results contribute to the ongoing discussion about the relationship between diet and health, particularly the mortality outcomes associated with vegetarian diets. The observation of lower mortality from IHD in vegetarians aligns with previous research, reinforcing the potential benefits of vegetarian diets for cardiovascular health. The study’s design and methodology, including the use of detailed questionnaires and the monitoring of mortality through the National Health Service Central Register, enhance the reliability of the findings. The consistent observation across multiple studies strengthens the conclusions about the overall health profiles of vegetarians and non-vegetarians in Britain, while acknowledging the limitations related to statistical power and the “healthy volunteer effect.”