Reaching new heights

Hong Kong teenagers have grown significantly over the past three decades as both boys and girls are around two centimeters taller than their counterparts back in 1993, a study has found.

The Hong Kong Growth Study - commissioned by the government in 2018 and conducted by the Department of Health and medical schools of Chinese University and the University of Hong Kong - was aimed at updating the latest growth charts used to measure and monitor children's growth trends.

Researchers collected growth data -including height, weight and head circumference - from more than 21,000 babies, children and teenagers at hospitals, maternal and child-health centers, kindergartens and schools between 2019 and 2022, and found a significant increase in the height of the youngsters.

The department's community medicine (student health) consultant, Thomas Chung Wai-hung, said the difference in height and weight in 1993 and 2020 was more obvious during adolescence. He said those aged 18 are about two cm taller compared to 30 years ago, with boys increasing to 172.5cm from 170.9cm, and girls reaching 160.2cm from 158.2cm.

The charts in 1993 are no longer suitable for studying the growth of children, he said.

"The updated charts can help us have a more accurate situation of children's growth nowadays. We used recent statistics in the new charts so medical staff and parents can have a better understanding of their health condition," Chung said.

"We still need further research to find out the reason for children and teenagers' growth. But other studies have shown that the changes in their height and weight are related to changes in society and people's living habits."

CUHK pediatrics specialist Tony Nelson said the increase was caused by improved nutrition and that a similar trend has been seen in many other places such as Japan and Europe.

The study also showed that newborns in Hong Kong are lighter compared to a World Health Organization study in 2006, while children aged three to five, especially girls, are shorter compared to those overseas.

But Nelson said the difference was due to local genetics and shows the importance of having local data.

"Our local data show that for the Hong Kong population, it's not like the WHO study which was from six countries like the Netherlands, India, America and other places. So I think this just reflects the local population here," he said.

"We also showed in our study that the mean age of birth is slightly below what the WHO was calculating, so this is also why babies are a little bit lighter at birth but they catch up later so it's all quite normal."

Due to the significant long-term growth in the data, authorities will put the updated charts in use from July this year at maternal and child-health centers, Chung said.

Student health service centers and public hospitals will also use the new charts from September, he added.

Chung said the Department of Health will switch from the current weight for height standard to body mass index when assessing whether a child is overweight. The change will avoid classifying normal-weight individuals as overweight, he said.

A surge in children's height has also been recorded in the mainland, with Beijing raising the standard height last year.

For example, the standard height for a six-year-old boy rose to 118.8cm from 117.7cm compared to a decade ago, with a six-year-old girl's standard height surging to 117.5cm from 116.6cm.

Pediatrician Alvin Chan Yee-shing said doctors can use the charts to assess children's health, nutrition, lifestyle and effectiveness of their treatment.

"Some kids with long-term illness have to take steroid drugs and the growth charts can help doctors assess whether their height has been affected," he said. The charts can also help detect abuse cases, Chan said.

wallis.wang@singtaonewscorp.com