to foster physical health. For example, in one study, if teens wrote letters of gratitude to other people over a month, they were more inclined to eat healthier food. Arguably, when people feel grateful, they feel an obligation to reciprocate the efforts of other individuals. Therefore, rather than indulge and sacrifice their own health—a behavior that would dismiss the efforts that other individuals invested in them—they may feel compelled to live a healthier life. Also, gratitude tends to elicit positive emotions, and these positive emotions tend to focus attention on favorable possibilities in the future. Individuals become more inclined to engage in behaviors that could benefit this future, such as healthy eating. Likewise, individuals who express gratitude also demonstrate improved overall health by way of greater physical activity, better sleep, fewer health care visits, and better nutrition. In addition, practicing gratitude may be correlated with small improvements in cardiovascular health. Relationship to altruism Gratitude has also been shown to improve a person's altruistic tendencies. One study conducted by David DeSteno and Monica Bartlett (2010) found that gratitude is correlated with economic generosity. In this study, which used an economic game, increased gratitude was shown to directly mediate increased monetary giving. From these results, this study shows that grateful people are more likely to sacrifice individual gains for communal profit. A study conducted by McCullough, Emmons, & Tsang (2002) found similar correlations between gratitude and empathy, generosity, and helpfulness towards the creation of social reciprocity even with strangers that is beneficial to the individuals in the short and in the middle terms. As a motivator of behavior Gratitude may also serve to reinforce future prosocial behavior in benefactors. For example, one experiment found that customers of a jewelry store who were called and thanked showed a subsequent 70% increase in purchases. In comparison, customers who were called and told about a sale showed only a 30% increase in purchases, while customers who were not called at all showed no increase in purchases. Here, the gratitude expressed by thanking the customer resulted in a significant increase in sales for the store. In another study, a restaurant's regular patrons gave bigger tips when servers wrote "Thank you" on their checks. In both cases, even simple expressions of gratitude led the benefactors to react favorably. The evidence of gratitude increasing prosocial behaviors is highly supported as it plays a very central role in guiding