Abstract
The body mass index (BMI) is widely used in clinical practice and medical examinations to evaluate the body size. People are considered obese when their BMI exceeds 25kg/m2 in Japan. Along with a recent increase in the prevalence of obesity in developed countries, health checkups and health care advice with a particular focus on metabolic syndrome were started in Japan a few years ago. As a result, people started to become aware of metabolic syndrome as well as the health risks of obesity, showing the success of such health care advice. On the other hand, it is not well-known that the number of people who are underweight with a BMI of less than 18.5 is increasing among Japanese women in their 20-40s. However, no common framework for underweightness has been established. Does being underweight have negative effects on our health? It is known that BMI has a U-shaped relationship with the mortality rate. In Asia, Zheng et al. reported the impact of a low BMI on mortality in 2011 involving more than 1 million people. In Japan, Tamakoshi et al. and Nagai et al. also reported a relationship between underweightness and high mortality rates. Other than reports on relationships with mortality rates, many reports indicated health damage caused by being underweight. These reports suggest that being underweight is associated with health risks. Thus, in this study, we investigated 13,499 subjects (males: 10,917, 81.2%, mean age: 47.4±10.6 years) who underwent a comprehensive medical examination, and reported the prevalence of diseases and results of the examination according to their body size. We also discussed issues regarding medical examinations when examining a person who is underweight based on the above results and previous studies.