TOKYO -- The hearing abilities of younger Japanese people aged in their 40s or under have progressively gotten worse since the beginning of the millennium, according to a major study conducted by a team including researchers at Keio University.
The team published its findings of the analytical study -- one of the largest of its kind in the world -- in the British medical journal The Lancet Regional Health. Generally, there is a decline in an individual's ability to hear as they age, but the hearing capabilities of examined subjects deteriorated so much over 20 years that one age group recorded hearing levels equivalent to those normally experienced among individuals up to 20 years older than them.
The World Health Organization (WHO) has stated that people are at risk of hearing loss due to unsafe listening habits, and has warned of hearing damage stemming from widespread usage of portable music players. However, the actual nature of hearing damage among young people had previously been unknown.
Hearing statistics for some 30,000 individuals were collected from 2000 to 2020 at the Tokyo Medical Center, based in the capital's Meguro Ward, and the team analyzed data of 10,681 subjects aged between 10 and 99 -- excluding individuals whose hearing was impaired due to ear-related disorders. The subjects' ability to hear was assessed by testing their auditory sensitivity of pitch and loudness by combining frequencies ranging from 125 to 8,000 hertz with sound levels measuring from 0 to 110 decibels.
Although hearing data of some 1,000 subjects had existed in Japan, there were issues with precision, among other factors. In the United States, the largest set of data comprised around 5,000 subjects, but subjects reportedly consisted mainly of individuals aged 50 or above.
The Keio University team calculated the average hearing abilities of each age group from those in their teens to their 90s for the first time in the world. It examined the changes in hearing for each age group.
The research found that individuals of both sexes aged in their 40s or younger tended to have increased difficulty in hearing high-pitched sounds of 4,000 hertz. Tests conducted between 2016 and 2020 revealed that these individuals found it hard to hear sounds unless they were louder by 0.8 to 2.4 decibels compared to sound levels required in the period from 2000 to 2004.
In terms of hearing age, the group that saw the biggest deterioration in hearing was women in their 20s, who had a hearing age 20 years older than their actual age. In other words, it can be said that women in their 20s between 2016 and 2020 had the same hearing abilities as women in their 40s between 2000 and 2004.
When comparing hearing faculties recorded during the two half-decade periods, men aged between 10 and 19 saw a decay in hearing age by 19 years, while women in the same age group saw a decay by 10 years. Other declines stood at 15 years for men in their 20s, six years for men in their 30s, 11 years for women in their 30s, seven years for men in their 40s, and eight years for women in their 40s.
It is known that the ability to pick up high-pitched sounds with a frequency of 4,000 hertz can be damaged due to exposure to excessive noise, and a team representative said, "There is a high possibility that an environment of listening to music has contributed to the results." There was no change in hearing among individuals aged in their 50s or above.
Koichiro Wasano, auditory disorders lab chief at the Tokyo Medical Center, commented, "If your hearing is damaged at a young age, it is possible that hearing abilities will deteriorate even further when you get older. I'd like young people to use these results to consider taking measures, like limiting the maximum volumes of devices when listening with earphones or headphones."
The hearing statistics for each age group in the study are set to be included in publications that will be used nationwide as otolaryngology textbooks. They will also be applied in medical checkups in the future.
While the study was large, the recent findings do not necessarily present an accurate picture of averages for the Japanese population, as the research targeted individuals who had visited a medical institution, and because that many of them were residents of Tokyo. It is expected that the data will become more precise if statistics can be gathered nationwide, including results collected outside medical institutions.
(Japanese original by Ryo Watanabe, Science & Environment News Department)