Abstract
Background: There have been mixed results reported internationally when associating vegetarian dietary patterns with all-cause and cause-specific mortalities. Objectives: This study aimed to extend our previous results by evaluating, with a larger number of deaths (N = 12,515), cause-specific mortalities comparing different vegetarian types with nonvegetarians. Methods: This prospective study used data from the Adventist Health Study-2 cohort. Mortality was ascertained between study baseline, 2002–2007, and follow-up through 2015. Dietary data were collected at baseline using a validated quantitative food frequency questionnaire and then categorized into 5 dietary patterns: nonvegetarian, semivegetarian, pescovegetarian, lacto-ovovegetarian, and vegan. Main outcomes and measures include all-cause and cause-specific mortalities using Cox proportional hazards regression models and competing risk methods. Results: The analytic sample included 88,400 participants who provided 971,424 person-years of follow-up. We report results as estimated at ages 65 and 85 y owing to age dependence of many hazard ratios (HRs). Compared with nonvegetarians, vegetarians had lower risks of mortality, overall (HR: 0.89; 95% confidence interval [CI]: 0.83, 0.95; HR: 0.98; 95% CI: 0.91, 1.04), from renal failure (HR: 0.52; 95% CI: 0.38, 0.70; HR: 0.65; 95% CI: 0.55, 0.76), infectious disease (HR: 0.57; 95% CI: 0.40, 0.82; HR: 0.90; 95% CI: 0.70, 1.17), diabetes (HR: 0.51; 95% CI: 0.33, 0.78; HR: 0.69; 95% CI: 0.53, 0.88), select cardiac (HR: 0.75; 95% CI: 0.65, 0.87; HR: 0.89; 95% CI: 0.83, 0.95), and ischemic heart disease causes (HR: 0.73; 95% CI: 0.59, 0.90; HR: 0.84; 95% CI: 0.75,0.94). Vegans, lacto-ovovegetarians, and pescovegetarians were also observed to have lower risks of total mortality and several similar cause-specific mortalities. However, higher cause-specified neurologic mortalities were observed among older vegetarians (estimated at age 85 y), specifically stroke (HR: 1.17; 95% CI: 1.02, 1.33), dementia (HR: 1.13; 95% CI: 1.00, 1.27), and Parkinson disease (HR: 1.37; 95% CI: 0.98, 1.91). Results in Black subjects for vegetarian/nonvegetarian comparisons largely followed the same trends, but HRs were less precise owing to smaller numbers. Conclusions: Vegetarian diets are associated with lower risk for all-cause and many cause-specific mortalities, especially among males and in younger subjects. However, higher risks are observed among older vegetarians for stroke and dementia. These results need further support and investigation.
Generated Summary
This prospective study utilized data from the Adventist Health Study-2 cohort, a large prospective cohort study of 95,863 Seventh-day Adventist (SDA) males and females in the United States and Canada recruited between 2002 and 2007. The objective of this study was to take advantage of the longer follow-up (median: 11.07 y) of the Adventist Health Study (AHS)-2 cohort, providing more precise estimates of associations between vegetarian dietary patterns and cause-specific mortalities, and by including separate analyses for Black subjects. Data on dietary patterns were collected at baseline using a validated quantitative food frequency questionnaire, categorized into five dietary patterns: nonvegetarian, semivegetarian, pescovegetarian, lacto-ovovegetarian, and vegan. The main outcomes and measures included all-cause and cause-specific mortalities, using Cox proportional hazards regression models and competing risk methods. The analytic sample included 88,400 participants who provided 971,424 person-years of follow-up. The analysis considered the associations of vegetarian dietary patterns with all-cause mortality, adjusting for sex, race, and region; then in addition to model 1, nonprevalent disease variables: marital status, education, BMI, exercise, smoking, alcohol, and female variables (model 2); and subsequently adding those prevalent diseases not believed to mediate dietary effects on outcomes (model 3).
Key Findings & Statistics
- The analytic sample included 88,400 participants providing 971,424 person-years of follow-up.
- The number of deaths during follow-up was 12,515.
- Crude mortality was 1.28% per person-year.
- At age 65 y for both sexes combined, HR for mortality in vegetarians was 0.89 (95% CI: 0.83, 0.95).
- Vegetarian males at age 65 y had an HR of 0.81 (95% CI: 0.73, 0.90).
- For lacto-ovovegetarians at age 65 y, HR was 0.88 (95% CI: 0.81, 0.95).
- Pescovegetarians at age 65 y, HR was 0.85 (95% CI: 0.76, 0.95), and at age 85 y, HR was 0.90 (0.86, 0.99).
- Comparing vegetarians with nonvegetarians among Black participants, HR was 0.90 (95% CI: 0.82, 0.99) for males and females combined, and HR was 0.84 (95% CI: 0.71, 0.99) for males only.
- In males, lacto-ovovegetarians at age 65 y had HR of 0.73 (95% CI: 0.54, 0.99).
- Pescovegetarians males (with no age dependence) had HR of 0.65 (95% CI: 0.48, 0.88).
- A vegetarian diet was associated with a lower hazard of death from renal failure (HR: 0.52; 95% CI: 0.38, 0.70) and from infectious diseases (HR: 0.57; 95% CI: 0.40, 0.82) at age 65 y, compared with nonvegetarians.
- At age 85 y, lower predicted hazards in vegetarians for deaths due to renal failure (HR: 0.65; 95% CI: 0.55, 0.76).
- Higher HRs, but only at age 85 y, were observed among vegetarians for stroke (HR: 1.17; 95% CI: 1.02, 1.33), and dementia (HR: 1.13; 95% CI: 1.00, 1.27).
- At age 65 y, vegans showed marked reductions in renal failure deaths (HR: 0.37; 95% CI: 0.17, 0.77), as did lacto-ovovegetarians (HR: 0.45; 95% CI: 0.30, 0.66).
- Pescovegetarians had significantly fewer deaths from infectious causes (HR: 0.41; 95% CI: 0.19, 0.86).
- CIs for all neurologic causes of death included the null.
- For those aged 85 y, predicted HRs and 95% CI remained significantly lower for renal failure (HR: 0.65; 95% CI: 0.55, 0.76).
- Lacto-ovovegetarians had a higher risk of stroke (HR: 1.20; 95% CI: 1.04, 1.39) and Parkinson disease (HR 1.44; 95% CI: 1.01, 2.04).
- Compared with nonvegetarians, vegetarians were older, proportionately more non-Black, married, current hormone replacement therapy users, and had higher minutes of exercise per week.
Other Important Findings
- Compared with nonvegetarians, vegetarians have lower risk of all-cause mortality, particularly for deaths at younger ages, and specifically for deaths associated with renal failure, infectious diseases, diabetes, select cardiac, and IHD causes.
- Pescovegetarian, lacto-ovovegetarian, and vegan vegetarian dietary patterns were also often inversely associated with these same disease-specific mortalities.
- Vegan (males and females combined) diet was not associated with all-cause mortality, although vegan males experienced lower mortality at younger ages only.
- The protective associations of vegetarian diets with all-cause mortality are consistent with previous results from the same cohort at a time of shorter follow-up, as well as earlier cohorts among SDA populations [8-10].
- The association of vegetarian diets with reduced fatal infectious disease in AHS-2 may be due to the favorable actions of certain nutrients present in these diets including vitamins, trace elements, and other phytochemicals to enhance immune response [50].
- The lower blood glucose in vegetarians [51] may be relevant, given that relative hyperglycemia is reported to reduce white cell phagocytosis [52].
Limitations Noted in the Document
- Information on dietary habits was only available from the baseline questionnaire and dietary patterns may have changed over time, although diets tend to be relatively stable in later adult years [55].
- Residual and unmeasured confounding remains possible because of the observational nature of the study, and errors in the dietary data are inevitable using an FFQ. Such errors typically bias HRs toward the null.
- The generalizability of results is another possible limitation, as participants from AHS-2 may differ from other cohorts in dietary and other lifestyle practices, although they are unlikely to differ in biological responsiveness to such diets and practices.
- The relatively health-conscious reference population is also a limitation, but despite this, many significant differences were observed.
- The study did not separate the vegan group by age.
Conclusion
The study’s findings reinforce previous research indicating the health benefits of vegetarian diets. The research highlights a lower risk of overall mortality among vegetarians, particularly in younger participants, with specific reductions in deaths related to renal failure, infectious diseases, diabetes, and heart-related illnesses. The study’s detailed analysis of various vegetarian diet types (vegan, lacto-ovo, pesco, and semi) further clarifies these benefits. However, the study also points out a concerning trend: older vegetarians, especially those following lacto-ovo and vegan diets, showed a higher risk of death from stroke and, in some cases, dementia and Parkinson’s disease. This could be due to the lack of the long chain n-3 fatty acids in the diet which is essential for brain health. These findings call for careful consideration of the types of vegetarian diets and a need for further research, especially regarding neurologic outcomes in older vegetarians. The observed associations between vegetarian diets and lower risks of all-cause mortality are particularly promising, with notable reductions in deaths related to kidney failure, infectious diseases, diabetes, and heart conditions. The protective associations of vegetarian diets with all-cause mortality are consistent with previous results from the same cohort at a time of shorter follow-up, as well as earlier cohorts among SDA populations [8-10]. The association of vegetarian diets with reduced fatal infectious disease in AHS-2 may be due to the favorable actions of certain nutrients present in these diets including vitamins, trace elements, and other phytochemicals to enhance immune response [50]. The lower blood glucose in vegetarians [51] may be relevant, given that relative hyperglycemia is reported to reduce white cell phagocytosis [52]. To our knowledge, this direct evidence of an association between vegetarian diets and infectious disease deaths is novel, possibly because nutritional epidemiology studies have more frequently focused on noncommunicable diseases. As the authors mention, more research is needed to fully understand the nuances of these relationships, especially with respect to stroke, dementia, and Parkinson’s disease, and to better determine the dietary factors that contribute to these risks. Ultimately, the study’s findings underscore the potential of vegetarian diets in promoting longevity and reducing the risk of several life-threatening diseases. However, the potential implications, especially as related to cognitive health, must be closely examined as the adoption of these diets continues to grow in popularity.