June 10, 2014

expert reaction to red meat intake and breast cancer incidence

An epidemiological study in the BMJ reported higher red meat intake in early adulthood might be associated with an increased risk of breast cancer.

Prof Paul Pharoah, Professor of Cancer Epidemiology, University of Cambridge, said:

“The investigators report an association between red meat consumption in women aged 26-45 in 1991 and the occurrence of breast cancer over the following twenty years.  The one fifth of women with the lowest intake of red meat had a risk of breast cancer of 161 per 100,000 women per year, whereas the one fifth of women with the highest intake of red meat had a risk of breast cancer of 195 per 100,000 per year.  These numbers were after adjusting for other factors known to be associated with a risk of breast cancer.  Thus the absolute increase in risk for women in the highest one fifth of red meat intake was 34 cases per 100,000 women per year or 6.8 additional breast cancer cases for every 1000 women over 20 years of follow up.

“This is equivalent to an absolute increase of 4.2 cases per 1000 women over 20 years for every additional portion of red meat eaten per day.  This is a very small increase in risk.

“It is important to note that this association does not necessarily imply causation.  The investigators have adjusted the findings for most known risk factors, but this adjustment may not be perfect and they were not able to adjust for some risk factors such as physical activity that are likely to be associated with red meat consumption.”

Dr Gunter Kuhnle, a food nutrition scientist at the University of Reading, said:

“Breast cancer can often be treated very well, but as with all serious illnesses, prevention is better than cure. Diet is an important risk factor in many cancers, as it has a long-term impact and can be easily modified by individuals. This new study from Harvard makes some interesting links between cancer, red meat consumption, and use of the contraceptive pill.

“Previous studies have not identified meat as a risk factor for breast cancer and the data available are largely inconclusive. However, many types of cancer develop slowly and the exposure to risk factors, such as diet, at an early age are likely to be important. In this study, the scientists tried to measure diet in adolescence using questionnaires. While this is of course prone to error – participants are unlikely to remember what they ate 20 years ago – it does provide a useful estimate.

“It is important to keep in mind that this is an observational study: the results report to show that people who reported a high meat intake have a higher risk of breast cancer, but correlation is not necessarily causation, and there is currently no explanation for the results. Red and processed meat have been linked to an increased risk of bowel cancer – probably because red and processed meat promotes the formation of carcinogenic compounds in the human gut – but a similar explanation for a link with breast cancer is currently not known.

“The results of this study are very interesting and will help scientists to investigate risk factors for breast cancer further. However, these results should not be used for scaremongering. People should also keep in mind that red meat is a valuable source of many nutrients for women, in particular iron, and can therefore be an important part of their diet.”

Professor Tim Key, a Cancer Research UK epidemiologist based at the University of Oxford, said:

“This research finds only a weak link between eating red meat and breast cancer and this study alone is not strong enough to change the existing evidence that has found no definite link between the two. Further studies are needed to clarify whether younger women who eat red meat have an increased risk of developing breast cancer.

“Women can reduce their risk of breast cancer by maintaining a healthy weight, drinking less alcohol and being physically active, and it’s not a bad idea to swap some red meat –  which is linked to bowel cancer – for white meat, beans or fish.”

Prof Valerie Beral, Director of the Cancer Epidemiology Unit and Professor of Epidemiology, University of Oxford, said:

“Dozens and dozens of studies have looked at breast cancer risk associated with some aspect of diet. The totality of the available evidence indicates that red meat consumption has little or no effect on breast cancer risk, so results from a single study cannot be considered in isolation.

“Diet is notoriously difficult to measure. The most reliable measure of meat consumption is whether or not people are vegetarian. Vegetarians do not have lower risks of breast cancer than non-vegetarians, further supporting other evidence that meat consumption is unlikely to play a major role in breast cancer.”

‘Dietary protein sources in early adulthood and breast cancer incidence: prospective cohort study’ by Maryam S Farvid et al. published in the BMJ at on Tuesday 10 June 2014.  

Declared interests

Gunter Kuhnle is part of the EU-funded consortium, PHYTOME, which conducts research into new meat products which reduce the risk of colorectal cancer.