by ecancer reporter Clare Sansom

Most current dietary advice suggests that diets rich in red meat can be associated with adverse health consequences including an increased risk of some types of cancer.

However, several large, reputable studies set up to investigate the link between red meat intake and breast cancer incidence have failed to prove such a link.

Almost all of the evidence obtained in these involved women in middle age and later, when most cases of breast cancer occur; there have been few such studies based on diet in adolescence and early adulthood.

Breast tissue is thought to be particularly vulnerable to carcinogens during adolescence, when the breasts are still developing and this tissue is proliferating rapidly.

A fairly small study published in 2008 suggested a link between red meat consumption during adolescence and risk of pre-menopausal breast cancer.

Maryam Farvid of the Harvard School of Public Health, Boston, Massachusetts, USA and her co-workers have now updated this study with a larger cohort and a longer follow-up period.

This study recruited a total of 47,355 women from the Nurses’ Health Study II (NHSII) cohort who were aged between 24 and 43 when that cohort was set up in 1989 and who had completed a further questionnaire in 1997 about their diet when at high school.

After excluding women who had been diagnosed with any cancer except non-melanoma skin cancer before 1998 and those with missing data, 44,231 women remained in the study.

Adolescent food intake was measured using a 124-item food frequency questionnaire that had been modified to include items that were commonly consumed when the participants were in high school (that is, from the 1960s to the early 1980s).

Protein items were grouped into processed and unprocessed red meat, poultry, fish, eggs, legumes and nuts, and nine frequency categories were used ranging from “less than once a month” to “six or more portions a day”.

Participants were also asked to complete a food frequency questionnaire every four years during the survey period, and little correlation was found between adolescent and adult food choices.

Breast cancer incidence in the study population was determined using biennial follow-up health questionnaires and by searching the National Death Index; cases of carcinoma in situ were not treated as breast cancers.

Potential confounding variables including race, age, body mass index, alcohol intake, smoking, family history of breast cancer, benign breast disease, age at menarche and menopausal status were obtained from the same biennial NHSII questionnaires.

Farvid and her co-workers documented a total of 1132 cases of breast cancer in this cohort during 13 years of follow-up; 546 of these cases were pre-menopausal, 483 post-menopausal and the other 103 of uncertain menopausal status.

The data was analysed using multivariable Cox regression models to allow for known major breast cancer risk factors.

A significant association (highest versus lowest quintiles relative risk 1.42; 95% confidence interval 1.05-1.94; Ptrend 0.007) was found between high levels of processed and unprocessed red meat consumption during adolescence and incidence of pre-menopausal breast cancer, but no association was found with post-menopausal breast cancer.

Interestingly, increased adolescent poultry consumption was found to be associated with a lower overall risk of breast cancer (RR 0.75; 95% CI 0.59-0.96 for an increase of one serving a day).

No association was found between adolescent consumption of fish, eggs, legumes or nuts and the risk of pre- or post-menopausal breast cancer.

The researchers estimated that replacement of one serving of red meat a day during adolescence with a serving of a combination of poultry, fish, legumes and nuts would reduce a woman’s overall breast cancer risk by 16% and her risk of pre-menopausal breast cancer by 24%.
No difference was observed when the results were stratified by hormone receptor status.

The association between adolescent meat intake and breast cancer risk was modified by alcohol intake during adolescence, with a more significant association among women who reported higher alcohol intake at the age of 18.

In conclusion, the authors suggest that replacing red meat with other sources of protein in the adolescent years may help girls reduce their subsequent risk of developing breast cancer, particularly before the menopause.

Reference

Farvid, M.S., Cho. E., Chen, W.Y., Eliassen, A.H. and Willett, W.C. (2014). Adolescent meat intake and breast cancer risk. Int. J. Cancer, published online ahead of print 15 September 2014. doi: 10.1002/ijc.29218.