The long-term perspective of life course models is important for understanding the health implications of these different dimensions of social ties for two general reasons. First, health behaviors change over time. Some habits (e.g., diet, exercise) take form in childhood, but others (e.g., smoking, drinking) are usually initiated in adolescence and early adulthood. Thus, relationships can mean different things for health depending on the stage of life considered, and their effects can filter across stages even as the relationships themselves change or fade (Repetti et al. 2002). For example, parents shape diet and exercise habits that contribute to childhood obesity, which, in turn, is associated with increased risk for cardiovascular disease and premature mortality in adulthood (Ferraro et al. 2003). As another example, peer relations often foster smoking and heavy alcohol consumption in adolescence and early adulthood, where they peak and then diminish thereafter, often because of new romantic partnerships (Bachman et al. 2002). Second, influential social ties change in both structure and content throughout life, with implications for health. For example, the most important relationship for health behavior in
