Abstract
Importance: Some evidence suggests vegetarian dietary patterns may be associated with reduced mortality, but the relationship is not well established. Objective: To evaluate the association between vegetarian dietary patterns and mortality. Design: Prospective cohort study; mortality analysis by Cox proportional hazards regression, controlling for important demographic and lifestyle confounders. Setting: Adventist Health Study 2 (AHS-2), a large North American cohort. Participants: A total of 96 469 Seventh-day Adventist men and women recruited between 2002 and 2007, from which an analytic sample of 73 308 participants remained after exclusions. Exposures: Diet was assessed at baseline by a quantitative food frequency questionnaire and categorized into 5 dietary patterns: nonvegetarian, semi-vegetarian, pesco-vegetarian, lacto-ovo-vegetarian, and vegan. Main Outcome and Measure: The relationship between vegetarian dietary patterns and all-cause and cause-specific mortality; deaths through 2009 were identified from the National Death Index. Results: There were 2570 deaths among 73 308 participants during a mean follow-up time of 5.79 years. The mortality rate was 6.05 (95% CI, 5.82-6.29) deaths per 1000 person-years. The adjusted hazard ratio (HR) for all-cause mortality in all vegetarians combined vs nonvegetarians was 0.88 (95% CI, 0.80-0.97). The adjusted HR for all-cause mortality in vegans was 0.85 (95% CI, 0.73-1.01); in lacto-ovo-vegetarians, 0.91 (95% CI, 0.82-1.00); in pesco-vegetarians, 0.81 (95% CI, 0.69-0.94); and in semi-vegetarians, 0.92 (95% CI, 0.75-1.13) compared with nonvegetarians. Significant associations with vegetarian diets were detected for cardiovascular mortality, noncardiovascular noncancer mortality, renal mortality, and endocrine mortality. Associations in men were larger and more often significant than were those in women. Conclusions and Relevance: Vegetarian diets are associated with lower all-cause mortality and with some reductions in cause-specific mortality. Results appeared to be more robust in males. These favorable associations should be considered carefully by those offering dietary guidance.
Generated Summary
This is a prospective cohort study that evaluated the association between vegetarian dietary patterns and mortality. The study used Cox proportional hazards regression, controlling for demographic and lifestyle confounders. The research was conducted within the Adventist Health Study 2 (AHS-2), a large North American cohort. The study assessed diet at baseline using a quantitative food frequency questionnaire and categorized dietary patterns into nonvegetarian, semi-vegetarian, pesco-vegetarian, lacto-ovo-vegetarian, and vegan categories. The primary outcome measure was the relationship between vegetarian dietary patterns and all-cause and cause-specific mortality, with deaths identified from the National Death Index. The study population comprised 73,308 participants after exclusions. The mean follow-up time was 5.79 years.
Key Findings & Statistics
- Mortality Rate: The mortality rate was 6.05 (95% CI, 5.82-6.29) deaths per 1000 person-years.
- All-Cause Mortality Hazard Ratios (HR):
- Vegetarians vs. nonvegetarians: HR 0.88 (95% CI, 0.80-0.97).
- Vegans vs. nonvegetarians: HR 0.85 (95% CI, 0.73-1.01).
- Lacto-ovo-vegetarians vs. nonvegetarians: HR 0.91 (95% CI, 0.82-1.00).
- Pesco-vegetarians vs. nonvegetarians: HR 0.81 (95% CI, 0.69-0.94).
- Semi-vegetarians vs. nonvegetarians: HR 0.92 (95% CI, 0.75-1.13).
- Cause-Specific Mortality Associations: Significant associations with vegetarian diets were detected for:
- Cardiovascular mortality.
- Noncardiovascular noncancer mortality.
- Renal mortality.
- Endocrine mortality.
- Baseline Characteristics:
- Vegans: 5548 participants (7.6%). Mean age: 57.9 years.
- Lacto-ovo-vegetarians: 21,177 participants (28.9%). Mean age: 57.5 years.
- Pesco-vegetarians: 7194 participants (9.8%). Mean age: 58.8 years.
- Semi-vegetarians: 4031 participants (5.5%). Mean age: 57.8 years.
- Nonvegetarians: 35,359 participants (48.2%). Mean age: 55.9 years.
- Mortality Rates by Dietary Pattern (per 1000 person-years):
- Vegans: 5.40 (95% CI, 4.62-6.17).
- Lacto-ovo-vegetarians: 5.61 (95% CI, 5.21-6.01).
- Pesco-vegetarians: 5.33 (95% CI, 4.61-6.05).
- Semi-vegetarians: 6.16 (95% CI, 5.03-7.30).
- Nonvegetarians: 6.61 (95% CI, 6.21-7.03).
- Mortality Risk in Men: The HR for all-cause mortality was 0.82 (95% CI, 0.72-0.94) among men.
- Mortality Risk in Women: The HR for all-cause mortality was 0.93 (0.82-1.05) among women.
- Cause-Specific Mortality Findings (Men combined with women):
- Vegetarians had a significantly reduced risk of renal mortality (HR, 0.48; 95% CI, 0.28-0.82).
- Vegetarians had a significantly reduced risk of endocrine mortality (HR, 0.61; 95% CI, 0.40-0.92).
Other Important Findings
- Associations in men were larger and more often significant than those in women.
- Vegetarian diets, especially pesco-vegetarian diets, showed reduced risk for IHD mortality.
- Vegetarian diets, especially vegan and lacto-ovo vegetarian diets, showed reduced risk for all-cause mortality.
- Vegetarian diets showed lower mortality for non-CVD, non-cancer causes.
- In men, significant reductions were observed for CVD and IHD mortality.
- Vegetarians had lower mortality rates compared to nonvegetarians.
Limitations Noted in the Document
- The study’s reliance on a single measurement of diet at baseline may not fully capture dietary changes over time.
- Potential for uncontrolled confounding from factors related to the conscious lifestyle choice of a vegetarian diet.
- Generalizability might be limited to other populations where attitudes, motivations, and applications of vegetarian diets may differ.
- Early follow-up may have biased the results toward the null, potentially underestimating the true associations.
- Variations in vegetarian dietary patterns and the definitions used across studies can affect the comparability of results.
- The study did not find significant associations with reduced cancer mortality, which may reflect insufficient statistical power.
Conclusion
The study’s findings indicate that vegetarian dietary patterns are associated with lower all-cause mortality and specific cause mortality. These results suggest that vegetarian diets, or diets with reduced meat consumption, may be associated with lower risk of death and should be considered carefully by individuals when making dietary choices and by those offering dietary guidance. The study demonstrated a consistent association over several decades, replicating previous results in a population with greater geographic and ethnic diversity. The evidence that vegetarian diets, or similar diets with reduced meat consumption, may be associated with a lower risk of death should be considered carefully by individuals as they make dietary choices and by those offering dietary guidance. The study highlighted that vegetarian dietary patterns were associated with a lower risk of death when compared to nonvegetarian patterns. The study notes that, “Vegetarian diets have been associated with more favorable levels of cardiovascular risk factors and nutrient profiles of the vegetarian dietary patterns suggest possible reasons for reduced cardiovascular risk such as lower saturated fat and higher fiber consumption.” The analysis within the non-CVD, noncancer category revealed notable reductions in mortality with underlying causes classified as endocrine or renal (diabetes mellitus and renal failure, in particular). These apparent protective associations seem consistent with previously published findings, showing an association of vegetarian diets with reduced risk of incident diabetes and of prevalent diabetes, hypertension, and metabolic syndrome.
IFFS Team Summary
- 73 000 Seventh Day Adventists followed for a mean of 5.8 years only, recruited 2002-2007. 2570 deaths calculated up to 2009.
- Vegan, Vegetarian, Fish eaters, and semi-vegetarians have benefit over non-vegetarians HR = 0.85, 0.91, 0.81, 0.92 Respectively)
- modest 10% reduction in cancers and 18% decrease in heart disease
- Study is ongoing, and requires more time for better statistical significance between the groups