Vegetarians have a lower risk than meat-eaters of developing at least five cancers, according to the largest study on the potential impact of diet on the development of the disease.
Scientists found vegetarians had less chance than omnivores of suffering pancreatic, breast, prostate, kidney and multiple myeloma blood cancers, although they showed a higher incidence of a main oesophageal malignant tumour.
The work does not prove causation but adds support to the idea that avoiding meat may help cut the likelihood of some cancers. It also poses questions about potential hazards to vegetarians and vegans from nutrient deficiencies.
“This study is really good news for those that follow a vegetarian diet because they have a lower risk of five cancer types, some of which are really prevalent in the population,” said Aurora Perez-Cornago, principal investigator of the study and formerly an associate professor at Oxford Population Health, part of the University of Oxford.
Vegetarians should make sure they supplement their diet with nutrients found in animal foods that might otherwise be missing from their diets, she added.
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The researchers examined data from more than 1.8mn people from India, Taiwan, the UK and US, according to a study published in the British Journal of Cancer on Friday. The sample comprised about 1.65mn meat eaters, 57,016 poultry eaters, 42,910 pescatarians, 63,147 vegetarians and 8,849 vegans. It was adjusted to account for various physical and lifestyle differences including body mass index, a rough measure of healthy weight.
The scientists found a lower risk for vegetarians of 31 per cent for multiple myeloma, 28 per cent for kidney cancer, 21 per cent for pancreatic cancer, 12 per cent for prostate cancer and 9 per cent lower risk of breast cancer. Their risk of squamous cell carcinoma of the oesophagus was almost double that of meat-eaters.
The cases of lower cancer risks for vegetarians might be because of their diets’ beneficial effects on the body’s metabolism, said Tim Key, co-author of the study and emeritus professor of epidemiology at Oxford Population Health. Previous research had shown vegetarians have substantially lower blood levels of a protein thought to indicate a higher risk of kidney cancer, he said.
The higher oesophageal cancer risk in vegetarians would need further investigation but might reflect a lower intake of micronutrients such as vitamin B12, which is found in red meat, poultry and fish, Key added.
Vegetarians were found to be no less likely than omnivores to get bowel cancer, a superficially surprising result given previous studies suggesting high consumption of red and processed meat raises the risk. A possible explanation is that the omnivores in the latest study ate modest amounts of meat on average, the researchers said.
The study found vegans were at higher risk of bowel cancer than meat eaters, although the small sample size of vegans meant the result should be interpreted with caution, the scientists said.
The study’s strengths included its 16-year follow-up, the large number of cancer cases recorded and its robust statistical analysis, said Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London.
The results were largely consistent with previous studies and a forthcoming piece of research from Imperial College, said Dagfinn Aune, a research fellow at the department of epidemiology and biostatistics at the London-based institution.
The newly published research contained “hints toward a lower risk for some additional cancers in vegetarians” but further work might be needed as the results were not statistically significant, Aune said.
Data visualisation by Alan Smith