With children spending more and more time on the internet, a health sciences professor is asking parents to consider trying an American mother's hands-on approach which sets firm rules and allows kids to have a healthier online life.

Zentaro Yamagata, professor of social medicine at the University of Yamanashi, and others who conducted research on children from Koshu, Yamanashi Prefecture, and their internet use found that junior high school students who exhibit the telltale signs of online addiction spend prolonged periods browsing the web -- meaning they devote less time to studying, physical activity and sleep.

A junior high school student views a smartphone in photo taken in Tokyo in September 2018. (Kyodo)

Too much screen time was also linked to depression, said Yamagata, who has been studying children for more than 30 years.

A nationwide study conducted by the education ministry and other bodies in fiscal 2014 revealed children who spend the most time on smartphones and other devices perform worse in Japanese language, arithmetic, mathematics and other tests.

Supplied photo shows Zentaro Yamagata, professor of social medicine at the University of Yamanashi. (Kyodo)

Hence, he argues, parents should think about placing appropriate parameters on their children's internet and gadget use, taking a page from Janell Burley Hofmann, a mother from Massachusetts whose "iPhone contract" blog to her then 13-year-old son went viral a decade ago.

"This attempt by an American mother drew global attention and can be used as a reference today (in Japan)," said Yamagata, referring to Hofmann's 18-point contract she had her son agree to before giving him his first iPhone for Christmas.

The list of rules and regulations started with the mother stating, "It is my phone. I bought it. I pay for it. I am loaning it to you," and later stipulated the device must be turned over to one of the boy's parents at night.

Hofmann warned her son against using "the technology to lie" or saying "anything through this device you would not say in person." She encouraged him to appreciate and view the physical world around him. "Take a walk. Talk to a stranger. Wonder without googling."

A survey by the Cabinet Office in fiscal 2021 found children of all ages in Japan spent more time on the internet than in the previous year. Those aged 10 to 17 used it an average of 4 hours, 24 minutes per day, while younger kids were online an average of 1 hour, 50 minutes.

The survey found that 97.7 percent of kids aged 10-17 and 74.3 percent of younger children said they use the internet, mainly to "watch videos" on smartphones, tablets, game consoles and television, among other devices.

In 2018, a health ministry research group estimated that 930,000 junior and senior high school students in Japan were addicted to the internet.

Although it is a useful tool for information gathering and communication, some data suggest the internet leads to a decline in academic ability. Experts such as Yamagata say parents and children should devise ways to utilize the internet's positive aspects while prioritizing real-world experiences.

In closing her contract with her son, Hofmann tells him even though she might have to confiscate his phone from time to time when he breaks the rules, "We will sit down and talk about it. We will start over again...I am on your team."

Yamagata says this clear stance from a parent to support their child's internet use in a healthy way, while acknowledging their desire to be online, is essential.

"We're not saying kids can't use the internet or smartphones. It's just that it's possible that the time necessary for a growing child to sleep, study, play outside and help at home is being reduced."

He suggested: "How about making a rule that you secure that necessary time first, and use the extra time for the internet or playing games?"