This large prospective cohort of AARP members provides no support for the hypothesis that intake of meat, meat cooked at high temperatures, well-done meat, or estimated intake of mutagens/carcinogens from meat are associated with increased risk of postmenopausal breast cancer. Furthermore, our results do not indicate that consumption of meat or meat cooked at high temperatures affected breast cancer risk in subgroups, such as obese or nulliparous women, consumers of alcohol, smokers, users of menopausal hormone therapy, or women with low physical activity or with a low intake of fruits or vegetables.
A recent analysis from the NIH-AARP study reported on the association of intake of red and processed meat in relation to the risk of 21 cancers. Positive associations were seen with several cancers, including those of the colorectum and lung, but not with breast cancer (25
). The present paper extends the findings of Cross et al. with regard to breast cancer by presenting more detailed results relating to meat preparation and intake of meat mutagens for the subcohort with complete meat module data.
In a previous publication from the NIH-AARP study (26
), saturated fat intake showed a significant positive association with postmenopausal breast cancer risk, hence, it's inclusion here as a covariate. However, in models omitting saturated fat intake, meat intake and use of high temperature preparation methods were not associated with breast cancer risk.
Previous epidemiologic studies that have examined the association of meat intake with breast cancer have yielded conflicting results. A meta-analysis of 31 studies with information on meat intake (27
) obtained a summary relative risk for the highest compared to the lowest level of total meat intake of 1.17 (95% CI 1.06-1.29). However, a pooled analysis of 8 cohort studies (3 of which were included in the meta-analysis) found no association with intake of total meat, red meat, or white meat (28
). In contrast to the meta-analysis, the pooled analysis included only cohort studies with at least 200 cases and which had used a validated food-frequency questionnaire and involved reanalysis of the raw data from each of the studies using a common approach. Our results are in agreement with those of the pooled analysis.
Of a smaller number of studies (both case-control and cohort) which examined meat preparation methods and/or degree of doneness of consumed meat and estimated intake of meat mutagens with breast cancer risk, several reported positive associations (6
), whereas others found no association (11
). Among those studies reporting positive associations, two found a strong association with HCA exposure or degree of doneness of meat (6
), whereas others observed a more modest association (9
). One study (10
) observed a modest association for intake of grilled or barbecued and smoked meats over the life course in postmenopausal (but not premenopausal) women but no associations with FFQ-derived measures of PAHs or HCAs based on type of meat, cooking methods, and doneness. Several studies examined possible interactions between intake of meat or well-doneness and polymorphisms in genes involved in the metabolism of HCAs and PAHs (11
). The results of these studies are inconsistent and several had very small numbers in the key subgroups to assess interactions (31
Strengths of the present study include the use of a detailed questionnaire to assess intake of different types of meat, meat preparation, and doneness preferences as well as a linked database to estimate exposure to meat mutagens. In addition, the present study had a wide range of variation in dietary intake. For example, among women in our study, median intake of red meat in the highest quintile was seven times that in the lowest quintile. Other strengths include the prospective nature of the study, completeness of follow-up, the large number of postmenopausal breast cancer cases, and the ability to adjust for a large number of potential confounding variables. The large sample size and the wide range of food consumption habits of the cohort enhanced the ability to detect an association and to examine possible interactions.
Limitations include the fact that we were not able to assess the association of meat-related variables with pre-menopausal breast cancer, due to the small number of such cancers in the cohort. Dietary intake based on FFQs is affected by measurement error (33
), which, if non-differential, could reduce an association. In this study, as in most previous studies, diet was assessed in midlife. Therefore, it is possible that meat intake and exposure to meat mutagens at a younger age, and particularly during adolescence when the breasts are developing, may affect the risk of breast cancer. We were also unable to examine the effect of genes involved in the metabolism of HCAs and PAHs, such as N
-acetyltransferase 1 (NAT1
) and N
-acetyltransferase 2 (NAT2
), cytochrome P450 1A2 (CYP 1A2
), and glutathione transferases (GSTs
In conclusion, results of this large prospective cohort of postmenopausal women do not support the hypothesis that a high intake of meat, red meat, processed meat, meat cooked at high temperatures, or meat mutagens is associated with increased risk of breast cancer.