Many studies have observed the effects of volunteerism (as a form of altruism) on happiness and health and have consistently found a strong connection between volunteerism and current and future health and well-being. In a study of older adults, those who volunteered were higher on life satisfaction and will to live, and lower in depression, anxiety, and somatization. Volunteerism and helping behavior have not only been shown to improve mental health, but physical health and longevity as well, attributable to the activity and social integration it encourages. One study examined the physical health of mothers who volunteered over a 30-year period and found that 52% of those who did not belong to a volunteer organization experienced a major illness while only 36% of those who did volunteer experienced one. A study on adults ages 55+ found that during the four-year study period, people who volunteered for two or more organizations had a 63% lower likelihood of dying. After controlling for prior health status, it was determined that volunteerism accounted for a 44% reduction in mortality. Merely being aware of kindness in oneself and others is also associated with greater well-being. A study that asked participants to count each act of kindness they performed for one week significantly enhanced their subjective happiness. It is important to note that, while research supports the idea that altruistic acts bring about happiness, it has also been found to work in the opposite direction—that happier people are also kinder. The relationship between altruistic behavior and happiness is bidirectional. Studies have found that generosity increases linearly from sad to happy affective states.