The suicide of a young woman who worked for advertising giant Dentsu Inc. was ruled as death by overwork, or "karoshi," after it was found she logged around 105 hours of monthly overtime.

Bereaved family members of Matsuri Takahashi, 24, and lawyers working on behalf of the family disclosed the finding by the Mita Labor Standard Inspection Office in Tokyo at a news conference on Oct. 7.

The labor office issued its ruling on Sept. 30.

It was not the first time a Dentsu employee has resorted to suicide as a result of being forced to clock up grueling overtime.

Takahashi worked for the agency's Digital Account division, which was in charge of online advertising and was recently discovered to have been engaged in systematic overbilling and deliberate cheating of customers.

Word of Takahashi's death coincided with the release of a labor ministry white paper to prevent deaths from overwork. Released on Oct. 7, it said labor standards inspection offices around the country recognized in fiscal 2015 that 93 suicides or attempted suicides resulted from overwork.

A young male employee of Tokyo-based Dentsu committed suicide in 1991 because of his long work hours. In a lawsuit filed by his bereaved family, the Supreme Court acknowledged in 2000 that the company is responsible for his death.

The acknowledgement paved the way for other courts to make the same judgment in other similar cases.

Takahashi joined Dentsu in April 2015 after graduating from the Faculty of Letters of the University of Tokyo. She was assigned to the Digital Account division.

According to the family's lawyers, her workload increased drastically from October. Her overtime from Oct. 9 to Nov. 7 alone amounted to 105 hours.

Takahashi took her life in a dormitory for Dentsu’s female employees on Dec. 25, 2015.

In the lead-up to her death, she contacted colleagues and friends through social networking services with distressing messages, such as “I want to die.”

The Mita inspection office recognized that the volume of Takahashi's workload increased sharply and her overtime work shot up drastically.

It concluded she suffered a mental breakdown due to the psychological burden of so much overtime work and committed suicide.

Last month, Dentsu admitted that the company had been engaged in fraudulent business practices, including overbilling of its clients, in divisions in charge of online advertisements for at least nearly four years from November 2012.

Dentsu blamed the scandal partly on a serious lack of manpower in the divisions concerned.

“We should have come to grips with the situation by increasing the number of staff in those divisions,” an executive of Dentsu said in a news conference in Tokyo on Sept. 23.

After the Supreme Court ruling in 2000, Dentsu said it would strictly monitor the working hours of employees.

According to lawyers, Dentsu instructed its employees to submit reports on their working conditions so that overtime work did not exceed the upper limits it had reported to the labor standard inspection office.

“We view our employee’s suicide very seriously," said a Dentsu representative who refrained from making further comment "as we have yet to grasp the contents (of the inspection office's judgment).”

When a suicide is recognized as a work-related death, the victim's bereaved family is allowed to claim benefits from the government-sponsored worker’s accident compensation insurance program.

(This article was written by Takuro Chiba and Tatsuro Kawai.)