TOKYO - Some 63 public school teachers in Japan died of overwork over a 10-year period up to 2016, the Mainichi Shimbun newspaper reported on Saturday (April 21), marking the first time that data for such cases are being made public and putting greater scrutiny on the long hours faced by the country's teachers.

While the working hours of Japanese teachers have been a long-standing problem, the government does not have available statistics on the number of teachers who die by overwork, making it hard to quantify the extent of the issue.

Cases of death by overwork, or karoshi, in Japan have often made the headlines, putting the country's notorious overtime culture under scrutiny.

Figures for the number of cases of educators who died from overwork are not included under the Ministry of Health, Labor and Welfare's annual report on 'karoshi' cases because they follow a different compensation system than those for workers at private institutions.

The Mainichi Shimbun said it obtained the figure through compiling data provided by the Fund for Local Government Employees' Accident Compensation based on the applications it received at its branch offices across Japan's 47 prefectures and 20 government-designated cities.

The data covered the death of teachers and local education board staffers who had succumbed to brain or heart conditions or committed suicide over mental health issues due to overwork.

Teachers covered in the data compiled included those who taught at the public kindergarten, elementary, junior high and high school levels.

According to the paper, in the academic years from 2007 to 2016, there were 63 certified cases of deaths by overwork out of 92 applications received.

Experts, however, say the actual number could be a lot higher as many bereaved families tend to suffer in silence rather than apply for recognition and compensation.

"Because awareness of working hours in schools has lagged behind, the reality is that it is difficult to even apply for government worker compensation," said Nobumoto Higuchi, a professor of education at Meisei University. "If the government is to promote work-style reform for educators, then it needs to first grasp the reality of the deaths caused by overwork - the worst result of long working hours."

Last year, it was revealed that a 31-year-old political reporter with Japanese broadcaster NHK died of heart failure in her sleep in July 2013 after clocking nearly 160 hours of overtime the month before.

In 2015, a rookie at advertising giant Dentsu leapt to her death after being subjected to a gruelling schedule and harassment at her workplace.