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New study associates intake of dairy milk with greater risk of breast cancer
Intake of dairy milk is associated with a greater risk of breast cancer in women, according to a new study conducted by researchers at Loma Linda University Health.
Dairy, soy and risk of breast cancer: Those confounded milks, published in the International Journal of Epidemiology, found that even relatively moderate amounts of dairy milk consumption can increase women’s risk of breast cancer — up to 80% depending on the amount consumed.
First author of the paper, Gary E. Fraser, MBChB, PhD, said the observational study gives“fairly strong evidence that either dairy milk or some other factor closely related to drinking dairy milk is a cause of breast cancer in women.
“Consuming as little as 1/4 to 1/3 cup of dairy milk per day was associated with an increased risk of breast cancer of 30%,”Fraser said.“By drinking up to one cup per day, the associated risk went up to 50%, and for those drinking two to three cups per day, the risk increased further to 70% to 80%.”
Current U.S. Dietary guidelines recommend three cups of milk per day.“Evidence from this study suggests that people should view that recommendation with caution,”Fraser said.
This raises the possibility that dairy-alternate milks may be an optimal choice.
Dr. Gary Fraser
Dietary intakes of nearly 53,000 North American women were evaluated for the study, all of whom were initially free of cancer and were followed for nearly eight years. Dietary intakes were estimated from food frequency questionnaires (FFQ), also repeated 24 hour recalls, and a baseline questionnaire had questions about demographics, family history of breast cancer, physical activity, alcohol consumption, hormonal and other medication use, breast cancer screening, and reproductive and gynecological history.
By the end of the study period, there were 1,057 new breast cancer cases during follow-up. No clear associations were found between soy products and breast cancer, independent of dairy. But, when compared to low or no milk consumption, higher intakes of dairy calories and dairy milk were associated with greater risk of breast cancer, independent of soy intake. Fraser noted that the results had minimal variation when comparing intake of full fat versus reduced or nonfat milks; there were no important associations noted with cheese and yogurt.
“However,”he said,“dairy foods, especially milk, were associated with increased risk, and the data predicted a marked reduction in risk associated with substituting soymilk for dairy milk. This raises the possibility that dairy-alternate milks may be an optimal choice.”
A hazardous effect of dairy is consistent with the recent AHS-2 report suggesting that vegans but not lacto-ovo-vegetarians experienced less breast cancer than non-vegetarians.
Fraser said the possible reasons for these associations between breast cancer and dairy milk may be the sex hormone content of dairy milk, as the cows are of course lactating, and often about 75% of the dairy herd is pregnant. Breast cancer in women is a hormone-responsive cancer. Further, intake of dairy and other animal proteins in some reports is also associated with higher blood levels of a hormone, insulin-like growth factor-1 (IGF-1), which is thought to promote certain cancers.
“Dairy milk does have some positive nutritional qualities,”Fraser said,“but these need to be balanced against other possible, less helpful effects. This work suggests the urgent need for further research.”
The study is part of the Adventist Health Study-2, a long-term health study exploring the links between lifestyle, diet and disease among members of the Seventh-day Adventist church. The Adventist Health Study is funded in part through the generosity of the Ardmore Institute of Health.
新聞出處：洛馬琳達大學健康學院
OXFORD ACADEMIC 國際流行病學雜誌
簡單翻譯：
牛奶不是一向被認為是健康的飲品嗎？但根據最新研究發現，牛奶和乳癌有關係，即使每天喝不到一杯牛奶的成年女性，罹患乳腺癌的風險可能增加多達 50%。
位於美國加州的洛馬琳達大學 (Loma Linda University) 的健康研究教授弗雷澤（Gary Fraser）的研究證明：喝牛奶和乳癌之間有密切關聯，他表示：「每天只喝四分之一至三分之一杯的牛奶，會增加 30% 的患乳腺癌的風險；每天喝一杯，相關的風險上升到 50%；而每天喝兩到三杯的人，風險會進一步上升到 70%到 80%。」
過去學術界的確有一種聲音，認為牛奶和乳癌有關係。這次弗雷澤領導的研究，追踪了整個北美近 53,000 名婦女的乳製品消費情況，歷時 8 年，比較了乳製品和豆製品的消費量。參加者的乳腺癌家族史、體力活動、飲酒、用藥以及生殖和婦科病史也考慮在內。到研究結束時，已診斷出 1,057 例新的乳腺癌病例。
儘管沒有發現大豆製品與乳腺癌之間的明確關聯，但是與那些喝牛奶很少或不喝牛奶的人相比，那些攝入較高牛奶的人患乳腺癌的風險更大。
弗雷澤說：「數據顯示，用豆漿代替乳製品的風險將顯著降低。」
研究人員並指出，食用全脂牛奶與低脂或脫脂牛奶對結果影響不大。
研究中還說，攝入乳製品和其他動物蛋白與血液中高水平的生長因子 IGF- 1 激素有關，該激素可誘發某些癌症。
弗雷澤說，儘管牛奶確實具有「一些積極的營養品質」，但會有乳癌風險，至於牛奶和其他癌症的關係，則需要進行更多的研究才能發現其聯繫度。
他提到，美國現行的《飲食指南》(Food Guide) 中建議成人每天喝三杯牛奶。「這項研究的證據表明，人們應該謹慎看待這一建議。」
