The truism that all adults need at least eight hours of sleep a night for good health should be put to rest by mounting evidence that less may be better.

• 成年人每天至少需要8小时睡眠才可以保持身体健康--这条"真理"已不再适用，因为越来越多的证据表明睡觉时间少于8小时可能会更有益于健康。