Abstract
Background: Vegetarians and others who do not eat meat have been observed to have lower incidence rates than meat eaters of some chronic diseases, but it is unclear whether this translates into lower mortality. Objective: The purpose of this study was to describe mortality in vegetarians and comparable nonvegetarians in a large United Kingdom cohort. Design: The study involved a pooled analysis of data from 2 prospective studies that included 60,310 persons living in the United Kingdom, comprising 18,431 regular meat eaters (who ate meat ≥5 times/wk on average), 13,039 low (less-frequent) meat eaters, 8516 fish eaters (who ate fish but not meat), and 20,324 vegetarians (including 2228 vegans who did not eat any animal foods). Mortality by diet group for each of 18 common causes of death was estimated with the use of Cox proportional hazards models. Results: There were 5294 deaths before age 90 in 1 million y of follow-up. There was no significant difference in overall (all-cause) mortality between the diet groups: HRs in low meat eaters, fish eaters, and vegetarians compared with regular meat eaters were 0.93 (95% CI: 0.86, 1.00), 0.96 (95% CI: 0.86, 1.06), and 1.02 (95% CI: 0.94, 1.10), respectively; P-heterogeneity of risks = 0.082. There were significant differences in risk compared with regular meat eaters for deaths from circulatory disease [higher in fish eaters (HR: 1.22; 95% CI: 1.02, 1.46)]; malignant cancer [lower in fish eaters (HR: 0.82; 95% CI: 0.70, 0.97)], including pancreatic cancer [lower in low meat eaters and vegetarians (HR: 0.55; 95% CI: 0.36, 0.86 and HR: 0.48; 95% CI: 0.28, 0.82, respectively)] and cancers of the lymphatic/hematopoietic tissue [lower in vegetarians (HR: 0.50; 95% CI: 0.32, 0.79)]; respiratory disease [lower in low meat eaters (HR: 0.70; 95% CI: 0.53, 0.92)]; and all other causes [lower in low meat eaters (HR: 0.74; 95% CI: 0.56, 0.99)]. Further adjustment for body mass index left these associations largely unchanged. Conclusions: United Kingdom-based vegetarians and comparable nonvegetarians have similar all-cause mortality. Differences found for specific causes of death merit further investigation. Am J Clin Nutr doi: 10.3945/ajcn.115.119461.
Generated Summary
This study presents a pooled analysis of data from two prospective studies conducted in the United Kingdom to investigate mortality rates in vegetarians and comparable nonvegetarians. The research utilized data from 60,310 participants, including regular meat eaters, low meat eaters, fish eaters, and vegetarians (including vegans), with mortality assessed for 18 common causes of death. Cox proportional hazards models were used to estimate mortality rates, and the study aimed to determine whether mortality differed significantly among the various dietary groups. The study’s methodology included a follow-up period of over one million person-years, with a focus on analyzing mortality before age 90 and comparing risk factors among the dietary groups.
Key Findings & Statistics
- Overall Mortality: There were 5294 deaths before age 90 in 1 million y of follow-up. The HRs for low meat eaters, fish eaters, and vegetarians compared with regular meat eaters were 0.93 (95% CI: 0.86, 1.00), 0.96 (95% CI: 0.86, 1.06), and 1.02 (95% CI: 0.94, 1.10), respectively.
- Statistical Significance: P-heterogeneity of risks = 0.082, indicating no significant difference in overall (all-cause) mortality among the diet groups.
- Circulatory Disease Mortality: Fish eaters showed higher risk compared to regular meat eaters (HR: 1.22; 95% CI: 1.02, 1.46).
- Malignant Cancer Mortality: Fish eaters had lower risk (HR: 0.82; 95% CI: 0.70, 0.97), including pancreatic cancer for low meat eaters and vegetarians (HR: 0.55; 95% CI: 0.36, 0.86 and HR: 0.48; 95% CI: 0.28, 0.82, respectively).
- Lymphatic/Hematopoietic Tissue Cancer: Vegetarians had lower risk (HR: 0.50; 95% CI: 0.32, 0.79).
- Respiratory Disease Mortality: Low meat eaters had lower risk (HR: 0.70; 95% CI: 0.53, 0.92).
- All Other Causes Mortality: Low meat eaters had lower risk (HR: 0.74; 95% CI: 0.56, 0.99).
- Dietary Intake: The values are based on data from the EPIC-Oxford study only.
- Protein intake as % of energy, was lowest in vegetarians and vegans (13.8%) and highest in regular meat eaters (18.2%).
- Plant protein intake as % of energy, was highest in vegetarians and vegans (7.8%) and lowest in regular meat eaters (5.8%).
- Total meat intake, g/d, was highest in regular meat eaters (106 g/d) and lowest in low meat eaters (35 g/d).
- Total fish intake, g/d, was similar in all non-vegetarian groups, roughly 40 g/d.
- Fresh vegetables, g/d, was highest in vegetarians (301 g/d) and lowest in regular meat eaters (256 g/d).
- Subgroup Analyses: Mortality analyses were also conducted for men, women, participants with different BMIs, and smoking statuses.
- Exclusion of Follow-up Data: When the first 2 years of follow-up were excluded, the heterogeneity of risk for all causes of death was no longer statistically significant (P-heterogeneity = 0.10; HRs not shown).
- Diet Group Changes: When data for participants known to have changed diet group at least once during follow-up were excluded, leaving data for 4270 deaths before age 90, there was no significant difference in risk between diet groups.
- Mortality Before Age 75: For all-cause mortality before age 75, there was no significant difference in risk between diet groups.
- P-Values for Heterogeneity: The P-value for heterogeneity across diet groups for all causes of death was 0.082 in the main analysis. The p-value for heterogeneity for circulatory disease mortality was 0.046. For malignant cancer, the p-value for heterogeneity was 0.12.
Other Important Findings
- BMI Adjustment: Further adjustment for body mass index left the associations largely unchanged.
- Study Cohorts: The study combined data from the Oxford Vegetarian Study (OVS) and the EPIC-Oxford cohort.
- Dietary Categories: The study categorized participants into regular meat eaters, low meat eaters, fish eaters, and vegetarians (including vegans).
- Dietary Fiber: Vegetarians and vegans consumed more dietary fiber than meat eaters.
- Nutritional Supplements: The proportions of men and women who reported regular use of nutritional supplements were highest in fish eaters and lowest in regular meat eaters.
- Comparison with Previous Studies: The findings align with previous research indicating no significant differences in all-cause mortality between vegetarians and nonvegetarians in the UK.
- Detailed Statistical Analysis: Cox proportional hazards regression was used to calculate HRs. The analyses were stratified by study protocol and adjusted for various factors including smoking, alcohol consumption, physical activity, marital status, and supplement use.
- Cancer Mortality: Fish eaters showed a lower risk of mortality from all malignant cancers combined.
- Pancreatic Cancer: Low meat eaters and vegetarians and vegans had significantly lower pancreatic cancer mortality.
- Lymphatic/Hematopoietic Tissue Cancer: Vegetarians and vegans combined had significantly lower cancer mortality from lymphatic/hematopoietic tissue.
Limitations Noted in the Document
- Data Limitations: The OVS recruitment questionnaire lacked the detail necessary for estimating nutrient intake, limiting the analysis to EPIC-Oxford data for dietary intake.
- Heterogeneity in Risk: There was some heterogeneity of risk between diet groups for specific causes of death (circulatory disease, cerebrovascular disease, and respiratory disease), although the patterns were not always clear.
- Dietary Group Changes: Excluding data from those who changed diet groups might have affected the overall findings.
- Generalizability: The study’s findings may not be directly generalizable to populations outside the UK due to dietary habits and other lifestyle factors.
- Inconsistent Results in Other Studies: Earlier studies, such as the AHS-2, produced inconsistent results in relation to all-cause mortality.
- Possible Mediators: The study acknowledges that differences in BMI between dietary groups may be related to the diet itself, thus potentially mediating some of the differences in risk.
Conclusion
The study provides valuable insights into the mortality patterns of vegetarians and comparable nonvegetarians in the United Kingdom. The primary finding indicates that there is no statistically significant difference in all-cause mortality between the dietary groups examined, which include regular meat eaters, low meat eaters, fish eaters, and vegetarians. However, the analysis highlights specific variations in mortality risk for certain causes of death. Fish eaters exhibited a higher risk for circulatory disease but a lower risk for malignant cancers. Moreover, vegetarians and vegans demonstrated lower mortality risks for pancreatic cancer and cancers of the lymphatic/hematopoietic tissue, which aligns with the findings of previous studies on cancer incidence within the same cohort. These observations suggest that while overall mortality may not significantly differ, specific dietary choices can influence the risk of developing certain diseases. The study’s emphasis on detailed statistical adjustments and subgroup analyses strengthens the credibility of these findings, and the inclusion of both OVS and EPIC-Oxford cohorts ensures a robust sample size and follow-up period. The study also acknowledges limitations, such as the impact of changes in diet group during follow-up and the potential for confounding variables, which should be considered in interpreting the results. Overall, the study contributes to the existing body of knowledge on the health implications of vegetarian diets, emphasizing that while all-cause mortality might not differ, the choice to avoid or limit meat consumption could influence the risk of developing specific health conditions.