Journal Name:
Int. J. Cancer
Article Title:
Dietary intakes of omega-6 and omega-3 polyunsaturated fatty acids and the risk of breast cancer
Date Written:
2009
Volume:
124
Number:
4
Page:
924
Author(s):
Thiébaut, A.C.; Chajès, V.; Gerber, M.; Boutron-Ruault, MC; Joulin, V.; Lenoir, G.; Berrino, F.; Riboli, E.; Bénichou, J.; Clavel-Chapelon, F
Article:
Breast cancer is the most frequent malignancy among women in Western Europe, North America and more recently in Japan. Many breast cancer deaths could be avoided through dietary modifications, although the available evidence is far from convincing for most dietary factors. The role of fat intake in breast cancer etiology has been investigated but still remains controversial. Epidemiologic studies have observed a significant increase in breast cancer risk with high saturated fat intake but no association with monounsaturated and polyunsaturated fatty acid (PUFA) intakes. Overall research has also demonstrated that omega-6 PUFAs show strong tumor-enhancing effects and omega-3 PUFAs nonsignificant protective effects. Additional experimental studies suggest that high intakes of omega-3 PUFAs could exert inhibitory effects on mammary tumorigenesis through competition with omega-6 PUFAs in metabolic outcomes.
The objective of this study was to assess the relationship between individual PUFA intakes estimated from diet history questionnaires and breast cancer risk among 56,007 French women. A secondary analysis of the potential interactions of omega-3 PUFA intakes with intakes of omega-6 PUFAs and vitamin E, a lipid soluble antioxidant, in relation to breast cancer risk, was also examined. During 8 years of follow-up, 1,650 women developed invasive breast cancer. A variety of foods were found to contribute to ALA intake: processed foods (28.2%) including nut mixes (12.1%), fruit and vegetables (16.4%), cheese (15.2%), butter and margarine (11.4%), meat (11.1%) and vegetable oils (8.7%).
Overall, breast cancer risk was not related to omega-6 (total, linoleic acid, arachidonic acid) or omega-3 (total, ALA, long-chain) PUFA intake, or the ratio of omega-6 to omega-3 PUFAs. However, opposite associations were seen according to food sources, suggesting other nutrients than PUFA may have a negative role in breast cancer. Breast cancer risk was inversely associated with alpha-linolenic acid (ALA) intake from fruit and vegetables [highest vs. lowest quintile, hazard ratio (HR) 0.74], and from vegetable oils (HR 0.83). The primary source of ALA in the diets of these women would be rapeseed/canola oil.
Conversely, breast cancer risk was positively related to ALA intake from nut mixes and processed foods, as was total ALA intake among women in the highest quintile of dietary vitamin E.
The epidemiologic evidence regarding ALA and breast cancer relationship is conflicting with both positive and negative associations between ALA intake and breast cancer risk being reported. A possible explanation for the lack of consistency among studies may be the different dietary sources of ALA, with meat being a major dietary source where positive associations have been found, whereas oils and raw vegetables were the main contributors in studies that have shown inverse associations. These results suggest that ALA intake may not have a direct biological effect on breast cancer occurrence but may reflect different food patterns involving other nutrients that could affect breast cancer risk. Whether all cis vs. cis/trans-ALA isomers originating from different food sources may exert different effects on carcinogenesis remains to be determined.
In conclusion, findings from this large French cohort indicate that the association of breast cancer risk with omega-6 and omega-3 PUFA intake may differ according to food sources, either reflecting different food patterns or geometrical isomers. The results of the study emphasize the need to distinguish among food sources of PUFAs, e.g., fish, vegetables, vegetable oils vs. processed foods and to consider interactions between omega-6 and omega-3 PUFAs when evaluating potential beneficial effects of high omega-3 PUFA intakes for breast cancer prevention. These results also emphasize the need to consider interactions between fatty acids and with antioxidants when evaluating associations between PUFA intakes and breast cancer risk.
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