The lifestyles greatly changed as the social structure, the economic status and the features of diseases afflicting people have changed following rapid development of information technology, an aging society and the internationalization. Under these circumstances, there is an important need for individuals to make active efforts to find scientific methods for the primary prevention of diseases and search for positive methods to improve their quality of life (QOL) while still healthy. We think it is important that individuals voluntarily and actively commit themselves to modifying their lifestyles to make it more stress-resistant and healthier. The overall lifestyle of individuals, including smoking, drinking and physical exercise, has been found to be associated with physical health, mental health. We examined the health potentials using health-related questionnaires, general health-check-up data, and the measurements of typical biomarkers such as lymphocyte chromosome alterations, natural-killer (NK) cell activity and serum IgE or cortisol levels among workers, elderly people, general populations, and the Hanshin-Awaji earthquake victims. We selected the 8 healthy lifestyles based on our previous studies and the health-related habits reported by Breslow. The 8 healthy lifestyles are 1) not smoking, 2) not drinking too much alcohol, 3) doing physical exercise regularly, 4) sleeping 7 to 8 hr per night, 5) keeping nutritional balance in meals, 6) not working more than 10 hr per day, 7) eating breakfast every day, and 8) keeping mental stress levels moderately. The Health Practice Index (HPI) was calculated by the number of good lifestyles. According to the results of 6-yr follow-up of 2148 workers, the unhealthy workers were found to have had significantly higher risks for the developments of chronic diseases. The NK cell activity was found to be significantly higher in the good-lifestyle workers. The genetic health status was estimated by the frequency of chromosomal alterations (sister chromatid exchange ; SCE, chromosomal structural aberrations, and micronuclei) in the blood lymphocytes. Individuals having good lifestyles showed a significantly lower level of chromosome alterations compared to those with poor lifestyles. The persons having unhealthy lifestyles showed abnormally high IgE levels. Earthquake victims reporting poor lifestyles or high posttraumatic stress disorder (PTSD) scores had lower natural killer (NK) cell activity and higher cortisol than those reporting healthy lifestyles. The data of the workers or the aged indicated the those people having good lifestyles or more human supports had higher quality of life scores in spite of having high job strain or low physical health status compared to those having poor lifestyles or low human supports. The reason why we recommended that people modify their lifestyles to a healthier life is that it is easier to achieve self-realization within our short life span, as one's lifestyle becomes healthier. In this sense, the creation of a healthier life will provide a source of reserve force, adaptive force, defensive force or resistive force against future loads which can destroy one's health.