Human Biology of Japan

This special issue of the Annals of Human Biology features articles under the general title of ‘The Human Biology of Japan’. Japan is the world's 4th largest island country made up of more than 6,800 islands of which Honshu, Hokkaido, Kyushu, Shikoku and Okinawa make up about 97% percent of Japan's land area and support the vast majority of the population of 126 million people. Forests and mountains cover over 70% of the land making habitation necessary on the coastal regions, primarily in high density cities resulting in over 90% of the population being urbanised. These characteristics of the 4th largest island country in the world make it an extremely interesting target for human biological research as demonstrated by the current issue of the Annals of Human Biology made up of contributions by our Japanese colleagues and guest edited by Professor Taro Yamauchi of Hokkaido University, Japan, and Dr Jun Ohashi of the University of Tokyo, Japan.

Knowledge of the pattern of human growth and adult phenotype is fundamental within our science and thus this journal issue is introduced by the presentation of national anthropometric reference values and growth curves for children (Inokuchi et al. this issue). They emphasise the variety of growth references that have been developed in Japan since the 1980s, their limitations and thus the need for the current nationally representative charts. The epidemiologic transition is a global phenomenon and obesity is one of its most widespread and persistent outcomes. Japan recognises obesity as one of its most serious public health concerns and Isojima and Yokoya (this issue) discuss and summarise the use of anthropometric indices for assessing childhood obesity in Japan focussing on the use of percentage overweight and BMI.

Japanese people, along with the closely related East Asians, are generally thinner than individuals of European ancestry, they are prone to accumulating visceral adipose tissues. Genome-wide discovery of loci influencing obesity-related traits, and application of the genome sequence data to assess the natural selection, provides evidence that the obesity-related traits in East Asians might be shaped by natural selection. Nakayama and Inaba (this issue) summarise the health and evolutionary implications of genetic variants influencing obesity-related traits in Japanese through a review of recently published papers of medical, genetic and evolutionary studies regarding obesity-related traits in the Japanese and closely related East Asians.

Physical activity and nutrition are the foci for interventions to improve health and reduce the risk for non-communicable disease. Using National Health and Nutrition Surveys, Tanaka (this issue) reviews the status of physical activity in Japan concluding that measurement accuracy is a problem in reaching a clear national picture for adults and children. The Japanese have the longest life expectancy in the world for both women (90.1 years) and men (85.4 years), with an overall average of 87.9 years. Yokoyama et al. (this issue) use the National Health and Nutrition Survey to investigate the intergenerational comparison of nutritional intake. The traditional Japanese diet called “Washoku” may be one of the factors that has helped to extend the lifespan and may form a basis for intervention in younger age groups. In this regard promoting continued physical activity is an important health promotion strategy among elderly individuals. Hasegawa et al. (this issue) evaluate the effect of a lower limb strength training programme on the daily step counts during the snowy season amongst elderly individuals recruited from a snowy-cold region of northern Japan. The intervention improved physical function, with a significant increase in step count among individuals with lower baseline strength, implying that lower limb muscle strengthening is an effective intervention to improve physical activity in this group.

Further research on postmenopausal Japanese women by Nishimura et al. (this issue) investigate serum TRACP-5b and BAP levels to determine their associations with the heel stiffness index measured by Quantitative Ultrasound. They conclude that higher rates of bone resorption are associated with a lower stiffness index and that high bone resorption affects bone mass more than bone formation, resulting in a low bone mass.

Japanese women are the focus for investigations by Ayabe et al. (this issue) of the association of appendicular muscle mass (AMM) and skeletal muscle mass index (SMI) with the history of exercise and/or physical activity. They conclude that both past and present participation in physical and/or sports activities plays an important role in maintaining appropriate SMI and AMM in young women.

Sato et al. (this issue) investigate the relationship between habitual fibre intake and postprandial glucose in early adulthood concluding that 7.0 g/1000 kcal of dietary fibre is an effective target value for a stepwise approach to nutrition education in Japan. Tsunetsuku and Ishibashi (this issue) have undertaken a fascinating study on the effects of plant odours on heart rate and its variability in infants age 1 to 3.5 months. Limonene, used to promote weight loss, prevent cancer, treat cancer, and treat bronchitis and as a flavouring in foods significantly reduced heart rate but increased its variability whilst the odour of pinene significantly reduced heart rate variability.

Finally Koganebuchi and Kimura (this issue) report on a review of the history, peopling and biomedical and genetic characteristics of the population of the Ryukyu Islands that stretch southwest from Kyushu to Taiwan. They cover an area of 4,624 km² and support a population of over 1.5 million people. Morphological and genetic studies have suggested that Ryukyuans have a complex demographic history. In viral infectious diseases, some strains that may be associated with disease symptoms are specific to Ryukyuans. Dramatic changes in diet play an important role among Ryukyuans in terms of decreased longevity and changes in mortality lifestyle-related diseases. To achieve a better understanding of pathogenic disease factors, further integration of findings regarding the genetic and biomedical characteristics of the Ryukyuans is needed.

Disclosure statement

No potential conflict of interest was reported by the authors.