Longitudinal Associations Between Vegetarian Dietary Habits and Site-Specific Cancers in the Adventist Health Study-2 North American cohort.

in The American journal of clinical nutrition by Gary E Fraser, Fayth M Butler, David J Shavlik, Roy O Mathew, Jisoo Oh, Rawiwan Sirirat, Dmitry Abramov, Lars E Sveen

TLDR

  • Vegetarians were found to have a lower risk of developing all cancers combined and medium frequency cancers, particularly colorectal, stomach, and lymphoproliferative cancers.
  • The study suggests that a vegetarian diet may be beneficial for cancer prevention.

Abstract

Associations between vegetarian diets and risk of common cancers are somewhat understood, but such data on medium frequency cancers is scarce and often imprecise. To describe multivariable-adjusted associations between different types of vegetarian diets (compared with non-vegetarians) and risk of cancers at different bodily sites. The Adventist Health Study (AHS-2) is a cohort of 95863 North American Seventh-day Adventists, established between 2002-2007. These analyses used 79,468 participants initially free of cancer. Baseline dietary data were obtained using a food frequency questionnaire, and incident cancers by matching with state and Canadian provincial cancer registries. Hazard ratios (HR) were estimated using proportional hazards regression. Small amounts of missing data were filled using multiple imputation. Over all cancers, all vegetarians combined compared to non-vegetarians, had HR=0.88 (95% CI 0.83,0.93; p<0.001), and for medium frequency cancers HR=0.82 (95% CI 0.76, 0.89; p<0.001). Of specific cancers, colorectal HR=0.79 (95% CI 0.66, 0.95; p=0.011), stomach HR=0.55 (95% CI 0.32, 0.93; p=0.025), and lymphoproliferative HR=0.75 (95% CI 0.60,0.93; p=0.010) cancers, were significantly less frequent among vegetarians. A joint test that HR=1.0 for all vegetarian subtypes compared with non-vegetarians, was rejected for cancers of the breast (p=0.012), lymphoma (p=0.031), all lymphoproliferative cancers (p=0.004), prostate cancer (p=0.030), colorectal cancers (p=0.023), medium frequency cancers (p<0.001), and for all cancers combined (p<0.001). These data indicate lower risk in vegetarians for all cancers combined, also for medium frequency cancers as a group. Specific cancers with evidence of lower risk, are breast, colorectal, prostate, stomach, and lymphoproliferative subtypes. Risk at some other sites may also differ in vegetarians, but statistical power was limited.

Overview

  • The study aimed to investigate the associations between different types of vegetarian diets and the risk of various types of cancer.
  • The study used the Adventist Health Study (AHS-2), a cohort of 95863 North American Seventh-day Adventists, established between 2002-2007.
  • The primary objective of the study was to describe multivariable-adjusted associations between different types of vegetarian diets and the risk of cancers at different bodily sites.

Comparative Analysis & Findings

  • The study found that vegetarians had a lower risk of developing all cancers combined, with a hazard ratio (HR) of 0.88 (95% CI 0.83,0.93; p<0.001).
  • Vegetarians were found to have a significantly lower risk of developing medium frequency cancers, with an HR of 0.82 (95% CI 0.76,0.89; p<0.001).
  • Specifically, vegetarians had a lower risk of developing colorectal, stomach, and lymphoproliferative cancers, while the risk of breast, prostate, and lymphoma cancers did not differ significantly between vegetarians and non-vegetarians.

Implications and Future Directions

  • The findings suggest that a vegetarian diet may be associated with a lower risk of developing various types of cancer, particularly medium frequency cancers.
  • The study highlights the importance of considering a vegetarian diet as a potential factor in the prevention of cancer, particularly in relation to colorectal, stomach, and lymphoproliferative cancers.
  • Future studies could investigate the specific components of a vegetarian diet that contribute to the observed protective effects, in order to inform dietary recommendations and inform policy.
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