 In  section 5,  we identified three groups of possible causal pathways between social determinants and health outcomes: childhood environment, material living conditions, and social and psychological factors. A central contributing factor to poor health outcomes, however, has an ambiguous relation to social determinants. There is strong evidence that health behaviors, including smoking, excessive alcohol consumption, poor nutrition, and lack of physical exercise are key contributors to morbidity and mortality (Petrovic et al. 2018). Some find, moreover, that health behaviors explain much of the social health gradient in high-income countries, since harmful health behaviors are more prevalent in groups with lower socioeconomic status (Petrovic et al. 2018). For example, Silvia Stringhini, Sabia, et al. (2010) argue that when superior measures of health behaviors are employed, much of the health gradient identified in the Whitehall II study can be explained by a social gradient in harmful health behaviors (though Stringhini, Dugravot, et al. [2011] did not replicate this finding in a study of employees of the French national gas and electric company, suggesting that whether health behaviors contribute to the social gradient may depend on social context).