The Rising Relative Risk of Mortality for Singles: Meta-Analysis and Meta-Regression
David J. Roelfs*, Eran Shor, Rachel Kalish and Tamar Yogev
Am. J. Epidemiol. (2011) 174 (4): 379-389.
Never-married persons (singles) constitute a growing demographic group; yet, the magnitude of the all-cause relative mortality risk for nonelderly singles is not known and important moderating factors have not been explored. The authors used meta-analysis to examine 641 risk estimates from 95 publications that provided data on more than 500 million persons. The comparison group consisted of currently married individuals. The mean hazard ratio for mortality was 1.24 (95% confidence interval: 1.19, 1.30) among multivariate-adjusted hazard ratios with a high subjective quality rating. Meta-regressions showed that hazard ratios have been modestly increasing over time for both genders, but have done so somewhat more rapidly for women. The results also showed that the hazard ratio decreased with age and that study quality has an important relation to hazard ratio magnitude.
Smoking Before the First Pregnancy and the Risk of Breast Cancer: A Meta-Analysis
Lisa A. DeRoo*, Peter Cummings and Beth A. Mueller
Am. J. Epidemiol. (2011) 174 (4): 390-402.
The authors conducted a meta-analysis of the association between smoking before a first pregnancy, when undifferentiated breast tissue may be vulnerable to tobacco carcinogens, and the risk of breast cancer. A search of the published literature through August 2010 identified 23 papers reporting on associations between smoking before a first pregnancy and breast cancer. Odds ratios or hazard ratios and 95% confidence intervals, adjusted for known or suspected breast cancer risk factors, were abstracted from each study. Data were pooled using both fixed- and random-effects models. The fixed-effect summary risk ratio for breast cancer among the women who smoked before their first pregnancy versus women who had never smoked was 1.10 (95% confidence interval: 1.07, 1.14); the random-effects estimate was similar. The separate fixed-effect risk ratios for smoking only before the first pregnancy (5 studies) or only after the first pregnancy (16 studies) were both 1.07, providing no evidence that breast tissue is more susceptible to malignant transformation from smoking before the first pregnancy. While these small summary risk ratios may represent causal effects, residual confounding could readily produce estimates of this size in the absence of any causal effect.
Aspirin Use, Body Mass Index, Physical Activity, Plasma C-Peptide, and Colon Cancer Risk in US Health Professionals
Xuehong Zhang*, Stephanie A. Smith-Warner, Andrew T. Chan, Kana Wu, Donna Spiegelman, Charles S. Fuchs, Walter C. Willett and Edward L. Giovannucci
Am. J. Epidemiol. (2011) 174 (4): 459-467
Aspirin use decreases colon cancer risk, but this association may vary among population subgroups. The aspirin-colon cancer association was evaluated according to body mass index and physical activity in 1,701 incident colon cancer cases diagnosed during follow-up of 139,310 participants for up to 26 years in 2 US prospective cohort studies that began in 1980 and 1992, respectively. Whether plasma C-peptide levels modified the association was examined by using a nested case-control design (n = 384 cases, 749 controls). Multiplicative and additive interactions were tested. Body mass index did not modify the association; pooled multivariable relative risks for regular aspirin use versus nonuse ranged from 0.74 to 0.75 in the normal weight and obese groups (test for multiplicative interaction, P = 0.75; test for additive interaction, P = 0.66). Pooled multivariable relative risks for regular aspirin use were 0.86 (95% confidence interval (CI): 0.66, 1.11) in the low and 0.67 (95% CI: 0.58, 0.77) in the high physical activity groups with no interaction evident on either the multiplicative or additive scale (P > 0.10). Plasma C-peptide levels also did not modify the aspirin-colon cancer association, with multivariable relative risks of 0.74 (95% CI: 0.50, 1.10) for the low and 0.65 (95% CI: 0.46, 0.92) for the high group. Reductions in colon cancer risk associated with aspirin use were not significantly modified by body mass index, physical activity, or plasma C-peptide level in this study.
Optimal Cutoff Values for High-Risk Waist Circumference in Older Adults Based on Related Health Outcomes
Noor Heim*, Marieke B. Snijder, Martijn W. Heymans, Dorly J. H. Deeg, Jacob C. Seidell and Marjolein Visser
Am. J. Epidemiol. (2011) 174 (4): 479-489
The authors aimed to explore optimal cutoffs for high-risk waist circumference (WC) in older adults to assess the health risks of obesity. Prospective data from 4,996 measurements in 2,232 participants aged ≥70 years were collected during 5 triennial measurement cycles (1992/1993–2005/2006) of a population-based cohort study, the Longitudinal Aging Study Amsterdam (Amsterdam, the Netherlands). Cross-sectional associations of WC with pain, mobility limitations, incontinence, knee osteoarthritis, cardiovascular disease, and diabetes were studied. Generalized estimating equations models were fitted with restricted cubic spline functions in order to carefully study the shapes of the associations. Model fits for applying different cutoffs to categorize WC in the association with all outcomes were tested using the quasi-likelihood under the Independence Criterion (QIC). On the basis of the spline regression curves, potential WC cutoffs of approximately 109 cm in men and 98 cm in women were proposed. Based on the model fit, cutoffs between 100 cm and 106 cm were equally applicable in men but should not be higher. In women, the QIC confirmed an optimal cutoff of 99 cm.