This is an excellent read from the Japan Times. It reports that scientists confirm that sleep deprivation has a detrimental impact on physical and mental health.
Source: Does Japan get enough sleep? | The Japan Times
This quite lengthy article looks at case studies in Japan and international research evidence.
It seems that of the OECD countries, Japan and Korea get the least sleep on average and France tops the league for sleep.
The article cites evidence that sleep deprivation can be seriously harmful and too much sleep can be problematic just like too little.