Japan is located in East Asia and consists of five large islands and numerous smaller islands, with a total of 6852 islands (Fig. 1). Mountainous areas cover 75% of the country, and the population is concentrated in the plains along the coast. Because it is an island nation and because of the policy of seclusion that lasted for more than 300 years during the Edo period, it is almost ethnically homogeneous. The total population is 125.36 million, ranking 11th in the world. The average life expectancy of men is 81 years, and that of women is 87 years, making Japan a country with one of the highest life expectancies in the world.