Why Japan's average height stopped growing while Korea, China surged

Japan's average height has barely changed since the 1990s, falling behind Korea and China. Researchers and media reports point to a possible combination of factors, including nutrition, maternal nutritional status and a lack of sleep.

In a report by Japanese financial daily The Nikkei on Saturday, it cited data published in the medical journal The Lancet in 2020 by the NCD Risk Factor Collaboration (NCD-RisC) that the average height of 5- to 19-year-olds in China and Korea increased at the world's fastest pace over the past 35 years, but Japan's remained stagnant.

According to the data, the estimated average height of 19-year-old Japanese males in 2019 was 172.1 centimeters and 158.5 centimeters for females. This leaves Japanese 19-year-olds about 3 to 5 centimeters shorter than their Korean and Chinese counterparts, where Korean males averaged 175.5 centimeters and females 163.2 centimeters, while Chinese males averaged 175.7 centimeters and females 163.5 centimeters.

Thirty-five years ago, the reverse was true. According to NCD-RisC estimates, Japan led the three countries in 1985 with an average height of 170.4 centimeters for 19-year-old males, compared to 168.7 centimeters in Korea and 167.6 centimeters in China.

Over the next 35 years, the estimated average height of 19-year-old Chinese males increased by 8 centimeters and Korean males by 6.8 centimeters, while Japanese males saw their height plateau, gaining just 1.6 centimeters. School health data from Japan's Ministry of Education, Culture, Sports, Science and Technology show a similar trend, with 17-year-old male students averaging 170.7 centimeters in 2000 and 170.8 centimeters in 2024.

Nutrition, pregnancy weight guidance, sleep examined as possible factors

Researchers point first to nutrition. Data compiled by Japan's National Institutes of Biomedical Innovation, Health and Nutrition show the country's daily per-capita caloric intake declined gradually after 1995 before leveling off.

According to statistics from U.N.'s Food and Agriculture Organization, daily per-capita energy supplies in Korea and China are 760 to 800 kilocalories higher than in Japan. The Nikkei reported that lower vegetable intake and diets deficient in calcium and vitamins among young people may also have contributed.

Maternal health guidelines limiting pregnancy weight gain are another leading factor. OECD data from 2021 show low-birth-weight infants — babies born weighing less than 2.5 kilograms — accounted for 10.2 percent of births in Japan, compared to 7.2 percent in Korea.

The Nikkei pointed out that long-standing guidance intended to limit weight gain during pregnancy to prevent hypertensive disorders may have affected fetal growth. The report also noted that dieting among young Japanese women to keep weight down may have contributed to lower birth weights.

A third hypothesis points to Japanese infants and toddlers getting less sleep. A 2010 study by researchers from the Children's Hospital of Philadelphia found Japanese children from birth to age 3 slept 11.62 hours a day, compared to 12.49 hours in China and 11.9 hours in Korea.

"We cannot draw a firm conclusion because there are no direct data, but shorter sleep duration among Japanese children may be one of several factors affecting later growth," Akifumi Kishi, an associate professor at the University of Tokyo, told The Nikkei.

The Nikkei report prompted discussion in Japan on social media platforms like X, formerly Twitter. Some users speculated without evidence that Japanese men's preference for petite women influenced the trend, in addition to the three factors highlighted in the report.

This article from the Hankook Ilbo, the sister publication of The Korea Times, is translated by a generative AI system and edited by The Korea Times.