乳癌:吃红肉会增加风险


  【24drs.com】一篇新研究显示,妇女在停经前几年常吃牛排、汉堡和红肉,其乳癌风险可能会高于蛋白质来源主要是禽类、鱼类、蛋类、坚果和豆类的妇女。
  
  麻州波士顿哈佛公卫学院营养系副教授Maryam S. Farvid博士等人在在线发表于6月10日BMJ期刊的报告指出,针对近90,000名妇女进行的分析中,大量摄取红肉与乳癌相对风险比肉类摄取量最少者高22%有关。
  
  作者们分析了参与「护士健康研究II」研究的88,803名停经前妇女的资料,「护士健康研究II」研究始于1989年,对当时年纪24-43岁的女性护士进行前瞻世代研究,她们平均年龄36.4岁(标准差4.6)。从这些护士们在1991、1995、2003和2007年完成有关饮食频率的问卷调查中,获得有关营养方面的资料,问卷询问在过去一年内对130种食物的一般摄取量。在1998年,这些妇女完成一份探讨她们在青春期时饮食摄取的类似问卷。研究对象也提供有关她们乳癌风险因素的资料,包括身高、体重、种族、初经年纪、产次、初次怀孕年纪、停经与否、口服避孕药的使用情况以及抽菸史。
  
  作者们使用Cox比例风险模式估计相对乳癌风险,他们也进行多变项分析,校正了种族、乳癌家族史、良性乳房疾病史、抽菸史、身高、身体质量指数、初经年龄、产次与初次生育年纪、口服避孕药使用情况、酒精与热量摄取、是否停经等。他们在初次分析使用的是1991年问卷的饮食资料,「因为那代表了成年早期的饮食摄取」。
  
  在88,803名妇女、追踪1,725,419人-年中,共有2,830例侵犯性乳癌:1,511例为停经前、918例已经停经、401例无法确定是否停经。1991年资料发现,相较于摄取红肉量最少者,摄取红肉最多者和停经前与停经后妇女后续发生乳癌相对风险(RR)达1.22倍有关(95%信心区间[CI]1.06 - 1.40;趋势P = .01)。校正总脂肪摄取量(最高与最低五分之一相比较、RR为1.20;95% CI,1.03 - 1.40;趋势P = .04),蔬果摄取量(RR,1.19;95% CI,1.04 - 1.37;趋势P = .03),血红素铁摄取量(RR,1.21;95% CI,1.04 - 1.41;趋势P = .03)之后,仍存在正相关。
  
  作者们写道,当把红肉摄取量纳为模式内的连续变项时,每天每增加一份红肉,与所有妇女的乳癌风险增加13%有关。校正青春期摄取的红肉量之后,相对风险并未显著改变。这个相对风险就数字上看或许不大,但是对乳癌而言,却是相当高的终身发生率,归因于红肉摄取的案例增加绝对数是相当大的,故有其公卫考量。
  
  禽肉类摄取量较高与乳癌风险较低有关(最高与最低五分之一相比较、RR为0.73;95% CI,0.58 - 0.91;趋势P= .02)。每天每增加一份禽肉类时,与停经后妇女的乳癌风险降低25%有关(RR,0.75;95% CI,0.58 - 0.98)。与停经前癌症风险无关。每天以一份禽肉类取代红肉,可降低乳癌风险17%(RR,0.83;95% CI,0.72 - 0.96)。每天用一份豆类取代一份肉类,可降低所有妇女之风险达15%(RR,0.85;95% CI,0.73 - 0.98)。此外,每天以综合鱼类、坚果、豆类、禽肉类取代一份肉类时,风险降低14%(RR,0.86;95% CI,0.78 - 0.94)。
  
  作者们写道,这些结果和其它研究并不一致,其它研究认为红肉摄取和乳癌风险无关,不过,多数研究结果来自中年之后的饮食分析,而成年早期的红肉摄取量和乳癌风险增加更相关。致癌的副产物,如高温烹煮肉类时产生的杂环胺和多环芳香烃;红肉的动物脂肪和血红素铁;刺激肉牛生长的外源性荷尔蒙的残余量,这些都是可以解释大量摄取红肉和乳癌之关联的可能机转。
  
  研究限制包括,研究对象主要是受良好教育的中产白人;依赖食物频率问卷可能会有误差;无法控制未知的其它干扰因素,研究强度包括,案例数多,前瞻型设计。
  
  作者们结论表示,这次的分析支持成年早期摄取较多红肉量和乳癌风险增加有关,并不仅限于停经前妇女之乳癌。与美国癌症协会指引一致的是,成年早期用豆类和禽肉取代未腌制与腌制红肉,有助于降低乳癌风险。
  
  资料来源:http://www.24drs.com/professional/list/content.asp?x_idno=7093&x_classno=0&x_chkdelpoint=Y
  

Breast Cancer: Red Meat Consumption May Raise Risk

By Norra MacReady
Medscape Medical News

Women who frequently eat steaks, burgers, and other sources of red meat during their premenopausal years may be raising their risk for breast cancer compared with women who get their protein mostly from poultry, fish, eggs, nuts, and legumes, a new study shows.

In an analysis of nearly 90,000 women, heavy consumption of red meat was associated with a relative risk for breast cancer 22% higher than that seen among women at the lowest end of the meat-eating spectrum, Maryam S. Farvid, PhD, Takemi fellow and associate professor from the Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, and colleagues report in an article published online June 10 in BMJ.

The authors analyzed data from 88,803 premenopausal women participating in the Nurses Health Study II, a prospective cohort study of female registered nurses who were 24 to 43 years of age in 1989, when the study began. Their average age was 36.4 years (standard deviation, 4.6 years). Nutritional information came from food frequency questionnaires the nurses completed in 1991, 1995, 2003, and 2007. The questionnaires asked about usual intake of 130 foods within the past year. In 1998, the women completed a similar questionnaire exploring their food intake during adolescence. The study participants also provided information about other breast cancer risk factors, including height, weight, race, age at first menarche, parity, age at first pregnancy, menopausal status, use of oral contraceptives, and smoking history.

The authors estimated relative breast cancer risk using Cox proportional hazard models. They also performed multivariate analyses, adjusting for race, family history of breast cancer, history of benign breast disease, smoking history, height, body mass index, age at menarche, parity and age at first birth, use of oral contraceptives, intake of alcohol and calories, and menopausal status. They used the dietary information from the 1991 questionnaire in their primary analysis, "as this represents the dietary intake in early adulthood."

There were 2830 cases of invasive breast cancer during 1,725,419 person-years of follow-up of 88,803 women: 1511 premenopausal cases, 918 postmenopausal cases, and 401 cases in which menopausal status was uncertain. Compared with women in the lowest quintile of red meat intake, the highest level of red meat intake in 1991 was associated with a relative risk (RR) of 1.22 for subsequent breast cancer in premenopausal and postmenopausal women (95% confidence interval [CI], 1.06 - 1.40; P for trend = .01). This positive association persisted after adjusting for total fat intake (RR for highest vs lowest fifth, 1.20; 95% CI, 1.03 - 1.40; P for trend = .04), fruit and vegetable consumption (RR, 1.19; 95% CI, 1.04 - 1.37; P for trend = .03), and intake of heme iron (RR, 1.21; 95% CI, 1.04 - 1.41; P for trend = .03).

"When total red meat intake was modeled as a continuous variable, each additional serving/day increase in total red meat was associated with a 13% increase in risk of breast cancer among all women," the authors write. The relative risk did not change significantly after adjusting for red meat intake during adolescence. "When this relatively small relative risk is applied to breast cancer, which has a high lifetime incidence, the absolute number of excess cases attributable to red meat intake would be substantial, and hence a public health concern," the authors write.

Higher levels of poultry intake were associated with a lower risk for breast cancer (RR for highest versus lowest fifth, 0.73; 95% CI, 0.58 - 0.91; P for trend = .02). Each additional daily serving lowered the risk for postmenopausal breast cancer by 25% (RR, 0.75; 95% CI, 0.58 - 0.98). There was no association with premenopausal cancer risk. Replacing 1 daily red meat serving with a serving of poultry lowered breast cancer risk by 17% (RR, 0.83; 95% CI, 0.72 - 0.96). Substituting 1 serving of legumes per day for a serving of meat lowered the risk among all women by 15% (RR, 0.85; 95% CI, 0.73 - 0.98). In addition, risk was lowered by 14% when fish, nuts, legumes, and poultry were combined to substitute for 1 serving/day of meat (RR, 0.86; 95% CI, 0.78 - 0.94).

These findings are not consistent with other studies, in which there was no association between red meat intake and breast cancer risk, the authors write. "However, most of the results have been derived from diet during midlife and later, and red meat intake during early adulthood may be more related to an increased risk of breast cancer. Carcinogenic byproducts such as heterocyclic amines and polycyclic aromatic hydrocarbons, created during high temperature cooking of meat; animal fat and heme iron from red meat; and hormone residues of the exogenous hormones for growth stimulation in beef cattle are some of the mechanisms that may explain the positive association between high intake of red meat and risk of breast cancer."

Study limitations include use of a predominantly white, well-educated, middle-class cohort; reliance on food frequency questionnaires, which usually include some measurement errors; and inability to control for unknown residual confounders. Strengths include the large number of cases and the prospective design.

"This analysis supports an association between higher consumption of total red meat during early adulthood and increased risk of breast cancer that was not clearly restricted to breast cancers in premenopausal women," the authors conclude. "Consistent with the American Cancer Society guidelines, replacement of unprocessed and processed red meat with legumes and poultry during early adulthood may help to decrease the risk of breast cancer."

This study was supported by a grant from the National Institutes of Health. The authors have disclosed no relevant financial relationships.

BMJ. 2014;348:g3437.

    
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