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21st March 2022
Individuals who are regular meat eaters have been found to be at a higher risk of all and some specific cancers compared to those who are either low meat eaters, pescatarians or vegetarians. This was the finding of a study of the UK Biobank database by researchers from the Cancer Epidemiology Unit, University of Oxford, Oxford, UK.
Cancer has been declared by the World Health Organization (WHO) as a leading cause of death worldwide accounting for nearly one in six of all deaths (10 million in 2020). Moreover, according to WHO, breast, lung, colorectal and prostate cancers are the most common forms of the disease. Understanding the causal relationship between dietary patterns or even particular dietary components and cancer aetiology and prevention is a challenge. For example, undertaking randomised controlled intervention trials to examine the association between diet and cancer outcomes are not feasible, for a number of reasons including cost, the difficulty of ensuring compliance among control and intervention groups as well as the long time-frame and exposure necessary to affect the carcinogenesis process. Although it has been shown that the risk of some cancers is lower in fish eaters and vegetarians than in meat eaters, it is not universally true with other work showing no statistically significant associations with dietary pattern and risk of premenopausal breast cancer.
For the present analysis, the Oxford team examined the relationship between those who ate meat at least 5 times a week, low meat consumers (< 5 times/week), pescatarians and vegetarians and the risk of all cancers and in particular, colorectal, postmenopausal breast and prostate cancers. They used data held in the UK Biobank and excluded individuals with a cancer diagnosis at recruitment. Participants completed an online questionnaire at recruitment into the database which asked about consumption and frequency of meat intake. The team also assessed whether specific hormones such as insulin-like growth factor-1 and testosterone as well as body mass index, might have potential mediator effects on the association between dietary patterns and cancer risk. The risks for the development of all and any of the specific cancers, were assessed using meat eaters as the reference group.
Meat eaters and cancer risk
A total of 247,571 individuals with a mean age of 56 years (46.4% female) were classed as meat eaters, 205,385 as low-meat eaters, 10,696 as pescatarians and 8,685 as vegetarians. After an average follow-up of 11.4 years, 54,861 incidence cases of cancer occurred; 5882 colorectal, 7537 women with postmenopausal breast cancer, 9501 men with prostate cancer.
After adjustment for several factors such as smoking status, physical activity etc, a vegetarian diet was associated with a 14% lower risk of all cancers compared to the reference group. (hazard ratio, HR = 0.86, 95% CI 0.80 – 0.93). This risk was also significantly reduced for breast cancer (HR = 0.82) and prostate cancer (HR = 0.69).
For pescatarians, there was also a lower risk of all cancers (HR = 0.90) compared to the reference meat group and for prostate cancer (HR = 0.80). For those categorised as low-meat eaters, the risks were only significantly lower for colorectal cancer (HR = 0.91).
After adjustment for possible mediators, only body mass index was found to be relevant and the risk of all cancers was slightly attenuated for vegetarians (HR = 0.88) and pescatarians (HR = 0.92) but remained significant. Furthermore, the reduced cancer risk remained significant among pescatarians and vegetarians but only for prostate cancer.
The authors concluded that being a pescatarian or vegetarian was associated with a lower risk of all cancers and that this might be attributable to differences in dietary factors in comparison to those who regularly eat meat. However, they added that it was unclear if these associations are causal or due to residual confounding, i.e., due to other, but unmeasured factors.
Watling CZ et al. Risk of cancer in regular and low meat-eaters, fish-eaters, and vegetarians: a prospective analysis of UK Biobank participants BMC Med 2022