Multiple imputation by chained equations (MICE) has emerged as a leading strategy for imputing missing epidemiological data due to its ease of implementation and ability to maintain unbiased effect estimates and valid inference. Within the MICE algorithm, imputation can be performed using a variety of parametric or nonparametric methods. Literature has suggested that nonparametric tree‐based imputation methods outperform parametric methods in terms of bias and coverage when there are interactions or other nonlinear effects among the variables. However, these studies fail to provide a fair comparison as they do not follow the well‐established recommendation that any effects in the final analysis model (including interactions) should be included in the parametric imputation model. We show via simulation that properly incorporating interactions in the parametric imputation model leads to much better performance. In fact, correctly specified parametric imputation and tree‐based random forest imputation perform similarly when estimating the interaction effect. Parametric imputation leads to slightly higher coverage for the interaction effect, but it has wider confidence intervals than random forest imputation and requires correct specification of the imputation model. Epidemiologists should take care in specifying MICE imputation models, and this paper assists in that task by providing a fair comparison of parametric and tree‐based imputation in MICE.

Background Developing an understanding of the biochemistry of aging in both sexes is critical for managing disease throughout the lifespan. Lipidomic associations with age and sex have been reported, but prior studies are limited by measurements in serum rather than plasma or by participants taking lipid-lowering medications. Methods Our study included lipidomic data from 980 participants aged 18–87 years old from the Genetics of Lipid-Lowering Drugs and Diet Network (GOLDN). Participants were off lipid-lowering medications for at least 4 weeks, and signal intensities of 413 known lipid species were measured in plasma. We examined linear age and sex associations with signal intensity of (a) 413 lipid species; (b) 6 lipid classes (glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, fatty acids, and acylcarnitines); and (c) 15 lipid subclasses; as well as with the particle sizes of three lipoproteins. Results Significant age associations were identified in 4 classes, 11 subclasses, 147 species, and particle size of one lipoprotein while significant sex differences were identified in 5 classes, 12 subclasses, 248 species, and particle sizes of two lipoproteins. For many lipid species (n = 97), age-related associations were significantly different between males and females. Age*sex interaction effects were most prevalent among phosphatidylcholines, sphingomyelins, and triglycerides. Conclusion We identified several lipid species, subclasses, and classes that differ by age and sex; these lipid phenotypes may serve as useful biomarkers for lipid changes and associated cardiovascular risk with aging in the future. Future studies of age-related changes throughout the adult lifespan of both sexes are warranted. Trial registration ClinicalTrials.gov NCT00083369; May 21, 2004.

The circadian system is a critical regulator of metabolism and obesity in males, but its role in regulating obesity in females is poorly understood. Because there are sex differences in the development of obesity and susceptibility to obesity-related disorders, we sought to determine the role of estrogens in regulating the circadian mechanisms underlying diet-induced obesity. When fed high-fat diet, C57BL/6J male mice gain weight, whereas females are resistant to diet-induced obesity. Here, we demonstrate that estradiol regulates circadian rhythms in females to confer resistance to diet-induced obesity. We found that ovariectomized females with undetectable circulating estrogens became obese and had disrupted daily rhythms of eating behavior and locomotor activity when fed a high-fat diet. The phase of the liver molecular circadian rhythm was also altered by high-fat diet feeding in ovariectomized mice. Estradiol replacement in ovariectomized females a fed high-fat diet rescued these behavioral and tissue rhythms. Additionally, restoring the daily rhythm of eating behavior in ovariectomized females with time-restricted feeding inhibited diet-induced obesity and insulin resistance. Together, these data suggest that the circadian system is a target for treating obesity and its comorbidities in women after menopause, when circulating levels of estrogens are too low to protect their circadian rhythms.

Objective:Children breast-fed during infancy consume more fruits and vegetables than formula-fed children. This pattern is likely due, in part, to infant learning from flavours of the mother’s diet transmitted through breast milk, but more research is needed to understand associations between early flavour exposures and later dietary patterns. We examined whether breast-feeding and maternal fruit and vegetable consumption during nursing were synergistically associated with higher child fruit and vegetable consumption.Design:Prospective cohort study of breast-feeding duration, maternal diet postpartum and child diet. Complete breast-feeding and maternal diet data were available for 1396 mother–child dyads; multiple imputation was used for missing data in other variables. In separate multivariable logistic regression models, we estimated the adjusted odds of high child fruit or vegetable consumption at 12 months or 6 years as a function of breast-feeding duration, maternal fruit or vegetable consumption during nursing, and their interaction.Setting:The Infant Feeding Practices Study II and Year 6 Follow-Up.Participants:Mother–child dyads followed from birth to 6 years during 2005–2012 in the USA.Results:Longer breast-feeding duration was associated with high child fruit and vegetable consumption at 12 months. At 6 years, the interaction between breast-feeding duration and maternal vegetable consumption was associated with high child vegetable consumption.Conclusions:Higher maternal vegetable consumption and longer breast-feeding duration were synergistically associated with high child vegetable consumption at 6 years, independent of sociodemographic characteristics and fruit and vegetable availability. Exposures to vegetable flavours through breast milk may promote later child vegetable consumption.

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Prior research on the relationship between veterans’ mental health and psychosocial functioning has primarily relied on male samples. Here, we investigated prospective longitudinal relationships between mental health and psychosocial functioning in 554 female Iraq and Afghanistan War veterans who were surveyed three times between two- and seven-years following separation from service. Mixed effects modeling revealed that increasing depression and posttraumatic stress disorder (PTSD) severity predicted declines in work functioning. Increasing PTSD severity predicted declining parental functioning and worsening depression predicted a decline in relationship functioning. In turn, decreased work and intimate relationship functioning predicted increased PTSD and depression symptom severity suggesting bi-directional effects between mental health and psychosocial functioning. An examination of the effect of deployment stressors on psychosocial functioning revealed that deployment sexual harassment was the strongest predictor of decreased psychosocial functioning across all domains. Evidence for the reciprocal nature of relationships between mental health and psychosocial functioning underscore the need for treatment targeted at PTSD and depression, as well as work and relationship functioning to improve outcomes for women veterans.

Objective: To determine whether the use of a multimodal analgesic protocol reduced short-term and long-term opioid use in patients hospitalized after orthopaedic trauma.