Essential workers in Japan's health care and transportation sectors were increasingly required to work excessive hours during the coronavirus pandemic, according to a government study released Friday.

Overall in the March and April period of the study, the percentage of people who worked for 80 or more hours per week fell, but in health care and transport, including postal and package delivery workers, it increased.

Overwork among transport workers increased 0.23 percentage point from a year earlier to 2.01 percent in March, according to the latest white paper analyzing overwork-related deaths and suicides in Japan. For those employed in health care, the figure rose 0.08 percentage point from the previous year to 0.68 percent.

In April, the trend remained roughly the same for the sectors, respectively.

The health care and transportation industries in Japan, plagued by cases of death due to overwork or suicide, have so far been exempted from implementing restrictions and penalties on employers for requiring staff to work excessively long hours.

Such reforms have been introduced to other sectors as part of the country's attempt to address the problem.

Meanwhile, the white paper found long consecutive hours on duty and graveyard shifts were the main reasons behind brain and heart disorders that could trigger overwork-related deaths.

Among the 2,280 cases of brain and heart disorders registered between fiscal 2010 and 2017 as work-related, the most common stress factors besides overwork six months prior to becoming ill included "long consecutive hours on duty," "shift-based work, graveyard shift," and "irregular work."

Looking into those who committed suicide due to work-related mental disorders and who had their deaths recognized as such under the workers' compensation program in fiscal 2015 and 2016, 40.1 percent were employed in industries needing specialized or technical knowledge, while 15.0 percent were in managerial positions.

Only around 30 percent of salaried workers said their working hours had decreased as compared to four or five years ago, while some 30 percent of self-employed people and corporate executives said the same, according to a labor ministry survey conducted from September to November last year.