The aging population has resulted in the percentage of GDP allocated to healthcare costs reaching about 10%, and further increases are expected. To manage this issue, the Ministry of Health, Labor, and Welfare is attempting to improve the population's lifestyle and to moderate healthcare cost increases by conducting medical checkups and providing health guidance for lifestyle improvements. The study data comprise medical prescriptions and medical examinations of 24,725 people who have developed diabetes and 13,453 people who have developed high blood pressure (data from the Japan Medical Data Center). Based on a multiple regression analysis, we compare people with good lifestyle habits and people with bad lifestyle habits to examine how the increases in their healthcare costs changed as a result of their diagnoses. For people who developed diabetes, those who properly controlled their BMI and LDL cholesterol levels, refrained from smoking and drinking, and exercised regularly (i.e., practiced good lifestyle habits) were able to maintain satisfactory medical examination results (diabetes). Based on these results, we prove statistically that the increase in healthcare costs is less for people who keep good lifestyle habits, even if they develop diabetes. Similarly, people who developed high blood pressure and practiced good lifestyle habits were able to maintain satisfactory medical examination results (high blood pressure). Again, the increase in the healthcare costs for this group was less, even if they developed high blood pressure, although, in this case, exercising regularly was not a relevant factor.