Building on what ProfX and apwsearch said, here’s the summary on an interesting paper finding a causal relationship between working moms and obese kids:
http://www.jcpr.org/policybriefs/vol4_num6.html
Maternal Employment and Overweight Children
Patricia Anderson, Kristin Butcher, and Phillip Levine
The proportion of children who are overweight in the United States has increased dramatically in recent decades, more than tripling since 1970. Weight problems may be one of the most significant health issues facing children today, and understanding the cause of this trend is critically important.
In their JCPR working paper, Maternal Employment and Overweight Children [Note: Here is a link to the whole paper: http://www.jcpr.org/wp/WPprofile.cfm?ID=323 ], Patricia Anderson, Kristin Butcher, and Phillip Levine explore one potential factor in the rise of childhood obesity: maternal employment. Maternal employment has more than doubled since 1970, and the authors ask whether the parallel rise in childhood obesity might be linked to employment, or whether the rise is purely coincidental. That is, would these children still be overweight even if their mothers did not work?
The authors find a direct, causal relationship between more intensive maternal employment and weight problems in children. Mothers who work more hours per week are more likely than mothers who do not work, or who work fewer hours, to have overweight children. Although the impact of maternal employment on children’s weight problems is significant, it explains only a small portion of the rise in childhood weight problems.
Maternal Employment and Children’s Weight
Roughly 12% of the approximately 10,000 children in the authors’ data set were considered overweight, and about one-fourth were at risk of being overweight. Although weight problems in childhood may be linked to both genetic and environmental factors, the recent rise in overweight is unlikely due to genetics, which change slowly. On the other hand, with the rapid increase in the fraction of mothers who work, children’s environments have changed rapidly, and this may have affected children’s weight. Time constraints, for example, may force working mothers to rely on high-calorie, prepared foods and fast foods. Children who are in child care may learn to eat according to a clock, rather than relying on natural indications of hunger. Unsupervised children may make poor nutritional choices for snacks and meals, and they may be less inclined to exercise. Research has found, for example, a correlation between television viewing and overweight among children. Mothers who work may not have the time or flexibility to breastfeed their children, and recent research has highlighted the importance of breastfeeding for both cognitive and physical outcomes. On the other hand, children of working mothers may participate in more after-school activities, which might increase their exercise levels. The authors explore these and other theories in their analysis of whether maternal employment affects a child’s weight.
Controlling for a large number of observable characteristics, the study finds that children whose mother’s worked more hours per week over the child’s lifetime are more likely to be overweight. However, there may be further, unobservable, differences between mothers who work more intensively and those who do not that would influence their children’s’ weight no matter how much mothers worked. To control for unobservable differences, the study compares the probability of overweight between siblings, where the mother’s work intensity differed between the children. The study finds that if a mother works more intensively during the childhood of some of her children, those children are more likely to be overweight than their siblings.
The intensity of work is critical. Additional weeks worked in a year have no effect, but working more hours per week increases the probability that the child will be overweight. Children whose mothers work an additional 10 hours per week experience nearly a 1 percentage point increase in the likelihood of being overweight. Thus, a mother working full-time (40 hours per week) would be expected to have a child with about a 2 percentage point higher probability of overweight than would a mother working part-time (20 hours per week). This suggests that the time constraints faced by mothers who work full-time may be contributing to weight issues. Time devoted to supervising her child’s diet and exercise may be limited when a mother works full-time, as may time for cooking and shopping for nutritious meals.
Although a mother’s employment contributes directly to a child’s weight problems, it can account for only 6%-11% of the growth in childhood weight problems. However, if the eating habits of children and their mothers are jointly affected by the rising time constraints, then the concomitant rise in maternal obesity should also be considered as a factor. This rise can account for about 11% of the increase in childhood obesity. Thus, even combining these two potential contributors still leaves most of the trend in childhood weight problems unexplained.
Study Description
The authors use data from the National Longitudinal Survey of Youth (NLSY), supplemented with data from the National Health and Nutrition Examination Survey (NHANES III), and the Continuing Survey of Food Intakes by Individuals (CSFII). The NLSY includes information on roughly 10,000 children. To control for unobservable maternal traits that may also affect their children’s health (i.e., unobserved heterogeneity), the authors compare data on siblings, as well as employ an instrumental variables model. Observable traits that are controlled in regression models include race and ethnicity, mother’s education and performance on an aptitude test, family size, birth order, whether the child was breastfed, the mother’s own weight, average family income over the child’s lifetime, and the child’s birth weight.
Patricia M. Anderson is an associate professor of economics at Dartmouth College and a faculty research fellow of the National Bureau of Economic Research; Kristin Butcher is a senior economist at the Federal Reserve Bank of Chicago; and Phillip B. Levine is an associate professor of economics at Wellesley College and a research associate at the National Bureau of Economic Research.