Background Japan, which currently maintains the highest life expectancy in the world and has experienced an impressive gain in adult height over the past century, has suffered a dramatic twofold increase in low birth weight (LBW) births since the 1970s.
Methods We observed secular trends in birth characteristics using 64 115 249 live births included the vital statistics (1969–2014), as well as trends in average height among 3 145 521 adults born between 1969 and 1996, included in 79 surveys conducted among a national, subnational or community population in Japan.
Results LBW rates exhibited a U-shaped pattern showing reductions until 1978–1979 (5.5%), after which it increased. Conversely, average adult height peaked for those born during the same period (men, 171.5 cm; women, 158.5 cm), followed by a reduction over the next 20 years. LBW rate and adult height showed a strong inverse correlation (men, r=−0.98; women, r=−0.88). A prediction model based on birth and economical characteristics estimated the national average of adult height would continue to decline, to 170.0cm (95% CI 169.6 to 170.3) for men and 157.9cm (95% CI 157.5 to 158.3) for women among those born in 2014.
Conclusions Adult height in Japan has started to decline for those born after 1980, a trend that may be attributed to increases in LBW births over time. Considering the known association between shorter adult height and adverse health outcomes, evidence of population-level decline in adult health due to long-term consequences of increasing LBW births in Japan is anticipated.
- epidemiology of chronic non communicable diseases
- birth weight
- health expectancy
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Contributors NM initiated the concept, designed and conducted the study, wrote the initial manuscript and approved the final manuscript as submitted. KY conducted literature review, provided important comments on the interpretation of the results and approved the final manuscript as submitted. SY and KYU oversaw the process and provided important intellectual context to the study design as well as interpretation of results, and approved the final manuscript as submitted. SVS provided important intellectual context to the study design as well as interpretation of the results, and approved the final manuscript as submitted.
Funding NM was supported by the Japan Society for the Promotion of Science (26870889), the Ministry of Health, Labour and Welfare (H28-ICT-ippan-001) and the Japan Agency for Medical Research and Development (AMED-6013). The funding sources had no involvement in the study design; the collection, analysis or interpretation of data; the writing of the report; or the decision to submit the article for publication.
Competing interests None declared.
Ethics approval The protocol for this study was approved by the Institutional Review Board of the National Center for Child Health and Development on 22 December 2016.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Annual rates of birth characteristics (in aggregated form) are available from the authors.