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Meat, dairy foods and risk of breast cancer

 

Many studies have investigated the association between meat and dairy food consumption and breast cancer risk, drawing different conclusions. This paper examines these associations by pooling results from eight large prospective studies.

Bottom line

This paper finds that meat and dairy product consumption, in mid or later life, is not associated with breast cancer risk (although it did not examine the effect of the level to which meat is cooked or cooking method).

Reference

SA Missmer et al. Meat and dairy food consumption and breast cancer: a pooled analysis of cohort studies. International Journal of Epidemiology 2002 31: 78-85.

Study selection

Studies were from the Pooling Project of Prospective Studies of Diet and Cancer. To be included, studies had to have at least 200 cases of breast cancer; assessed diet using a comprehensive food frequency questionnaire; and validated the questionnaire. Eight studies were identified with a total of 351,041 women, 7,379 of whom were diagnosed with breast cancer over five to ten years of follow-up. Ages ranged from 31 to 90 years.

The following were examined:

Meat

Dairy

Individual foods were only examined when intake had been assessed in at least five studies. The groups were analysed according to increments of 100g a day (or in a few cases 10g a day when more appropriate) and as quartiles (for main and sub-groups).

Results

Median total meat intake ranged from 25 g/day to 215 g/day between studies (half chicken breast = 86 g); median egg intake from 5 to 22 g/day (1 egg = 50 g); dairy fluids from 203 to 262 g/day (8 oz milk = 244 g); and dairy solids from 23 to 34 g/day (1 oz cheese = 28 g).

The results were adjusted for several variables (a total of 14) including age at menarche, menopausal status at follow-up, age at first birth, family history of breast cancer, smoking status, body mass index and alcohol intake.

No associations were found between total meat, red meat, white meat, total dairy fluids, total dairy solids and risk of breast cancer.

For 100 g/day intake increments, the relative risks and 95% confidence intervals were as follows: total meat 1.02 (0.97 to 1.08); red meat 0.98 (0.93 to 1.04); white meat 1.02 (0.94 to 1.11); total dairy fluids 0.99 (0.97 to 1.00); total dairy solids 1.03 (0.95 to 1.11).

Compared with the lowest quartiles of intake, the relative risks and 95% confidence intervals for the highest quartiles were as follows: total meat 1.08 (0.98 to 1.19); red meat 0.94 (0.87 to 1.02); white meat 1.02 (0.91 to 1.13); total dairy fluids 0.93 (0.84 to 1.03); total dairy solids 1.01 (0.93 to 1.09).

No associations were found between the meat or dairy sub-groups or specific meat or dairy foods and risk of breast cancer, with the exception of egg consumption (for 100 g/day increment, relative risk 1.22, 95% confidence interval 1.03 to 1.45).

Comment

Although an association was observed between egg consumption and breast cancer risk, this association became inconsistent in further analyses, and it is possible, even probable, that the association observed is due to chance. The probability of finding significant results due to chance increases with the number of statistical tests performed; and this analysis examined a large number of food groups and specific foods.

Although no association was observed between meat consumption and breast cancer risk, this paper was unable to assess the effect of cooking method or the level to which meat is cooked (as the majority of studies did not collect this information). For instance, meat cooked at high temperatures (e.g. frying and barbecuing) and welldone meat (especially to the point of charring) contain heterocyclic amines, known to be carcinogenic. However, the overall lack of association observed in this paper suggests that generally, there are no adverse effects of meat in relation to risk of breast cancer.