Cancer is the second leading cause of death globally, accounting for 1 in 6 deaths worldwide in 2018, according to the World Health Organization. Cancer is caused by both genetic and environmental factors, which vary depending on cancer type. Diet is known to be a major risk factor for multiple cancers, with processed and red meat being a risk factor for bowel cancer.
Previous studies have explored the association between vegetarianism and multiple common cancers, but associations with less common cancers have yet to be explored, and in research published in The American Journal of Clinical Nutrition, Gary Fraser and colleagues used cohort study data from The Adventist Health Study-2 (AHS-2) to assess the relationship between vegetarianism and risk of different uncommon and common cancer types. The study found that vegetarians had a 12% lower risk of developing cancer overall compared to non-vegetarians.
To observe the effects of diet and the odds of developing cancer, the study collected baseline data of participants from the AHS-2. This cohort study recruited more than 95,000 US and Canadian participants between 2002 and 2007, all of whom were volunteer members of the Seventh-day Adventist church. Dietary habits were obtained from a validated food frequency questionnaire. Vegetarians included those categorised as vegans (who avoided all animal products, consuming fewer than one such product per month), lacto-ovo-vegetarians (who avoided meat and fish but consumed eggs/dairy once or more per month), and pesco-vegetarians (who avoided meat but consumed eggs/dairy/fish once or more per month).
Cancer diagnosis (identified using the International Classification of Diseases version 10 and International Classification of Diseases, Oncology codes) was obtained by matching the AHS-2 data to cancer registries, with follow-up lasting from 2010 to 2013, depending on the US state and Canadian province/territory. In total, 79,468 participants were included in the study. Compared to non-vegetarians, vegetarians had a 12% lower risk of developing cancer overall. Vegetarians were also shown to have decreased risk of bowel cancer development, with a 45% lower risk of developing stomach cancer, a 20% lower risk of developing colon cancer, and a 21% lower risk of developing colorectal cancer. Other than bowel cancers, vegetarians had a lower risk of lymphoma and lymphoproliferative cancers compared to non-vegetarians, both with a 25% decreased risk.
The study by Fraser and colleagues provides further evidence of vegetarianism being a protective factor against bowel cancers, and also provides new evidence for vegetarianism being a protective factor against lymphoproliferative cancers. The study therefore provides an incentive to explore what aspects of vegetarianism protect against these cancers specifically. However, it is important to note that information on dietary habits was taken at the beginning of the study, which was subject to change during follow-up. GlobalData epidemiologists forecast that in the 16 major markets (16MM: Australia, Brazil, Canada, China, France, Germany, Italy, Japan, India, Mexico, Russia, South Africa, South Korea, Spain, the UK and the US), five-year diagnosed prevalent cases of colorectal cancer in men and women aged 18 years and over will increase from 4.6 million in 2025 to 5.4 million in 2031.