Nightshift work and risk of breast cancer and other cancers--a critical review of the epidemiologic evidence

OBJECTIVES: This systematic review concerns the role of nightshift work in the risk of breast cancer or other cancers. METHODS: Studies that specifically included information on nightshift or shift work and reported cancer occurrence were focused upon. A systematic search of Medline and the Science Citation Index was conducted until May 2007. The quality of each paper was discussed with respect to design, exposure and outcome information, bias, confounding, and exposure-response assessment. RESULTS: Thirteen relevant reports were found, and eight reported the relative risk for breast cancer, three for prostate cancer, three for colon cancer, and four for all cancers. Most of the studies had crude information about nightshift work, four register-linked studies had no individual exposure information but relied on exposure probabilities assessed on a group level, and no studies analyzed cancer risk according to the cumulative number of night shifts (however, most of the studies did so according to the number of years of nightshift work). Confounding did not seem to be of major concern. The presentation of the results was not always complete, and it would have been appreciated if the reasons for leaving some findings out had been reported. There were indications of a long-term effect of nightshift work (more than 20-30 years), but the number of positive studies was small. In addition, they were all conducted among nurses, and the risk estimates were only moderately increased. This situation makes the results sensitive to bias, chance, and confounding. CONCLUSIONS: There is limited evidence for a causal association between nightshift work and breast cancer, while there is insufficient evidence for prostate cancer, colon cancer, and overall cancer.     

Meat consumption and colorectal cancer: a review of epidemiologic evidence

This article reviews the epidemiologic evidence on colorectal cancer risk and meat consumption from 32 case-control and 13 cohort studies published in English from 1970 to 1999 and retrieved from the Medline database. The results support the hypothesis that meat consumption is associated with a modest increase in colorectal cancer risk. This association, however, seems to have been more consistently found for red meat and processed meat. The studies on cooking methods and meat "doneness" are not consistent and the evidence is not conclusive.     

Dichlorodiphenyldichloroethane burden and breast cancer risk: a meta-analysis of the epidemiologic evidence

The relationship of dichlorodiphenyltrichloroethane (DDT) exposure and breast cancer risk has received increasing attention since the beginning of the 1990s. Contradicting published results regarding the relationship between body burden levels of p,p'-dichlorodiphenyldichloroethane (p,p'-DDE)--the main DDT metabolite--and breast cancer, we argue that such differences stem from methodologic differences among those studies. We performed a meta-analysis of 22 articles using DerSimonian and Laird's method for random effects models. The Q-statistic was used to identify heterogeneity in the outcome variable across studies. The gradient of p,p'-DDE exposure in epidemiologic studies was homogenized to serum lipid bases (nanograms per gram). The potential for publication bias was examined by means of the Begg's test. We discuss methodologic features of the studies in an attempt to reconcile the findings. The summary odds ratio (OR) for selected studies was 0.97 (95% confidence interval, 0.87-1.09) and the gradient of exposure ranged from 84.37 to 12,948 ng/g. No overall heterogeneity in the OR was observed (chi-squared = 27.93; df = 23; p = 0.218). Neither the study design nor the lack of breast-feeding control or the type of biologic specimen used to measure p,p'-DDE levels were the causes of heterogeneity throughout the studies. Evidence for publication bias was not found (p = 0.253). Overall, these results should be regarded as a strong evidence to discard the putative relationship between p,p'-DDE and breast cancer risk. Nevertheless, the exposure to DDT during critical periods of human development--from conception to adolescence--and individual variations in metabolizing enzymes of DDT or its derivatives are still important areas to be researched in regard to breast cancer development in adulthood.     

A review of epidemiologic evidence that carotenoids reduce the risk of cancer

The epidemiologic evidence that carotenoids are involved in cancer etiology is evaluated. Low intake of vegetables and fruits and carotenoids is consistently associated with an increased risk of lung cancer in both prospective and retrospective studies. In addition, low levels of serum or plasma beta-carotene are consistently associated with the subsequent development of lung cancer. The simplest explanation is that beta-carotene is indeed protective. Since retinol is not related in a similar manner to lung cancer risk, beta-carotene seems to play a role that does not require its conversion into vitamin A. However, the importance of other carotenoids, other constituents of vegetables and fruits, and other nutrients whose levels in the blood are partially correlated with those of beta-carotene has not been adequately explored. In addition, smoking, a powerful risk factor for lung cancer, is associated with reduced intake of carotenoids and lowered blood levels of beta-carotene and has not always been adequately controlled in these analyses. Prospective and retrospective studies suggest that carotenoids may reduce the risk of certain other cancers; however, too few studies have looked at these sites to examine the consistency of the evidence. Although clinical trials of the efficacy of beta-carotene in cancer prevention are underway, it is still necessary and prudent to continue well-designed prospective and retrospective studies of the carotenoid hypothesis.     

出生体重与儿童期肥胖关联性的系统评价

目的 分析出生体重(BW)与儿童肥胖的关联性,为儿童肥胖预防提供依据。方法 通过数据库(PubMed,Elsevier和中国知网)检索BW与儿童肥胖发病相关的文献,用Meta分析方法评价BW与儿童肥胖发生风险的剂量反应关系。结果 本研究纳入32篇研究,共包括548 348名研究对象。与BW参照组(2 500~4 000 g)相比,高出生体重(≥4 000 g)是儿童肥胖的危险因素(OR＝1.77, 95%CI:1.66~1.89)。剂量反应Meta分析结果显示:随着BW的增加,儿童肥胖的发生风险也逐渐增加,且BW每增加100 g,儿童肥胖的发生风险大约增加1.1%。当BW达到3 575 g时,与儿童发生肥胖风险的剂量反应关系有统计学意义(P=0.046,OR＝1.08,95%CI:1.00~1.17)。且当BW＞3 575 g时,儿童肥胖的发生风险明显增加。结论 BW与儿童肥胖发生风险存在明显的J型剂量反应关系,且当儿童BW超过3 575 g时,儿童肥胖的风险明显增加。     

Processed meat and colorectal cancer: a review of epidemiologic and experimental evidence

Processed meat intake may be involved in the etiology of colorectal cancer, a major cause of death in affluent countries. The epidemiologic studies published to date conclude that the excess risk in the highest category of processed meat-eaters is comprised between 20% and 50% compared with non-eaters. In addition, the excess risk per gram of intake is clearly higher than that of fresh red meat. Several hypotheses, which are mainly based on studies carried out on red meat, may explain why processed meat intake is linked to cancer risk. Those that have been tested experimentally are (i) that high-fat diets could promote carcinogenesis via insulin resistance or fecal bile acids; (ii) that cooking meat at a high temperature forms carcinogenic heterocyclic amines and polycyclic aromatic hydrocarbons; (iii) that carcinogenic N-nitroso compounds are formed in meat and endogenously; (iv) that heme iron in red meat can promote carcinogenesis because it increases cell proliferation in the mucosa, through lipoperoxidation and/or cytotoxicity of fecal water. Nitrosation might increase the toxicity of heme in cured products. Solving this puzzle is a challenge that would permit to reduce cancer load by changing the processes rather than by banning processed meat.     

Trichloroethylene and cancer: systematic and quantitative review of epidemiologic evidence for identifying hazards

We conducted a meta-analysis focusing on studies with high potential for trichloroethylene (TCE) exposure to provide quantitative evaluations of the evidence for associations between TCE exposure and kidney, liver, and non-Hodgkin lymphoma (NHL) cancers. A systematic review documenting essential design features, exposure assessment approaches, statistical analyses, and potential sources of confounding and bias identified twenty-four cohort and case-control studies on TCE and the three cancers of interest with high potential for exposure, including five recently published case-control studies of kidney cancer or NHL. Fixed- and random-effects models were fitted to the data on overall exposure and on the highest exposure group. Sensitivity analyses examined the influence of individual studies and of alternative risk estimate selections. For overall TCE exposure and kidney cancer, the summary relative risk (RRm) estimate from the random effects model was 1.27 (95% CI: 1.13, 1.43), with a higher RRm for the highest exposure groups (1.58, 95% CI: 1.28, 1.96). The RRm estimates were not overly sensitive to alternative risk estimate selections or to removal of an individual study. There was no apparent heterogeneity or publication bias. For NHL, RRm estimates for overall exposure and for the highest exposure group, respectively, were 1.23 (95% CI: 1.07, 1.42) and 1.43 (95% CI: 1.13, 1.82) and, for liver cancer, 1.29 (95% CI: 1.07, 1.56) and 1.28 (95% CI: 0.93, 1.77). Our findings provide strong support for a causal association between TCE exposure and kidney cancer. The support is strong but less robust for NHL, where issues of study heterogeneity, potential publication bias, and weaker exposure-response results contribute uncertainty, and more limited for liver cancer, where only cohort studies with small numbers of cases were available.     

Association between spontaneous abortion and ergonomic factors. A literature review of the epidemiologic evidence

This article presents a literature review of seven epidemiologic studies which address the issue of spontaneous abortion and ergonomic factors. The following four ergonomic factors are analyzed: (i) shift work, (ii) piece work, (iii) posture, (iv) heavy lifting and physical effort. Among these factors, the last, heavy lifting and physical effort, is the only one that seems to be associated with an increased risk of spontaneous abortion.     

An epidemiologic study of breast cancer

A case-control study has been conducted in four areas of Canada in which 400 cases of breast cancer matched by age and marital status with neighborhood controls were administered medical and dietary questionnaires. The study is suggestive of an increased risk of breast cancer in post-menopausal women with younger age at menarche and an increased risk with delay of age at natural menopause. No protective effect of early age at first pregnancy was demonstrated in either pre- or post-menopausal women. An increased frequency of pregnancies of four months duration or less was found in cases compared to controls and a greater frequency in pre-menopausal cases compared to controls of a history of irregular menstrual periods. In pre-menopausal women no association has been found between increased height and weight as risk factors for breast cancer. For post-menopausal women, however, a weak association with increased height has been found, while a strong association with increased weight both at the time of menopause and the 12 months preceding diagnosis has ben confirmed.     

Dietary patterns and metabolic syndrome--a review of epidemiologic evidence

Metabolic syndrome is associated with increased risk of coronary heart disease and type 2 diabetes, and appears to be widely prevalent in both developed and developing countries. While lifestyle modification is recommended for management of the syndrome, the dietary pattern most beneficial for patients is yet to be ascertained. Original research papers from the Medline database were examined for dietary patterns that may be associated with the syndrome. Three large-scale epidemiological studies were found fitting our criteria. Dietary patterns high in fruit and vegetable content were generally found to be associated with lower prevalence of metabolic syndrome. Diet patterns with high meat intake were frequently associated with components of metabolic syndrome, particularly impaired glucose tolerance. High dairy intake was generally associated with reduced risk for components of metabolic syndrome with some inconsistency in the literature regarding risk of obesity. Minimally processed cereals appeared to be associated with decreased risk of metabolic syndrome, while highly processed cereals with high glycaemic index are associated with higher risk. Fried foods were noticeably absent from any dietary pattern associated with decreased prevalence of metabolic syndrome. The conclusion of this review is that no individual dietary component could be considered wholly responsible for the association of diet with metabolic syndrome. Rather it is the overall quality of the diet that appears to offer protection against lifestyle disease such as metabolic syndrome. Further research is required into conditions, such as overweight and obesity, which may influence the effect of diet on the development of metabolic syndrome.     

身体测量指标与胃癌发病风险的流行病学研究进展

胃癌是严重威胁人类健康的最重要恶性肿瘤之一。流行病学研究提示,身体测量指标与胃癌发病可能存在关联,目前研究结果尚不一致。本文通过查阅PubMed、万方数据知识服务平台等数据库文献,系统回顾了国内外关于身体测量指标与消化系统恶性肿瘤发病关系的前瞻性队列研究,并进行总结,结果显示,全身性肥胖和腹型肥胖可能与贲门癌发病风险相关,体重过轻与胃癌发病关联需进一步确证。本文从身体测量指标角度出发综述了胃癌发病的研究进展,以期为该领域未来研究方向提供思路,并为人群的胃癌防治提供科学依据。     

Antidepressant medication use and breast cancer risk

Experimental and epidemiologic studies suggest that antidepressant medication use may be associated with breast cancer risk. This hypothesis was investigated using a population-based case-control study; cases diagnosed in 1995-1996 were identified using the Ontario Cancer Registry, and controls were randomly sampled from an Ontario Ministry of Finance database. Data were collected using a self-administered questionnaire, and multivariate logistic regression was used to estimate odds ratios and 95% confidence intervals. Adjusted odds ratio estimates ranged from 0.7 to 0.8 and were not statistically significant for "ever" use of antidepressants, tricyclics, and selective serotonin reuptake inhibitors. Compared with no antidepressant use, use of tricyclic antidepressants for greater than 2 years' duration was associated with an elevated risk of breast cancer (odds ratio (OR) = 2.1, 95% confidence interval (CI): 0.9, 5.0). Of the six most commonly reported antidepressant medications, only paroxetine use was associated with an increase in breast cancer risk (OR = 7.2, 95% CI: 0.9, 58.3). Results from this study do not support the hypothesis that "ever" use of any antidepressant medications is associated with breast cancer risk. Use of tricyclic medications for greater than 2 years, however, may be associated with a twofold elevation, and use of paroxetine may be associated with a substantial increase in breast cancer risk.