Key points from article :
People aged 38 to 73 self-assesses on scale of morning or evening types.
Night owls are 10% more likely to have early deaths than morning larks.
Also 90% more likely to have psychological disorders.
Whole variety of unhealthy behaviours related to being up late by yourself.
40-70% of a person's body clock is genetic, rest can be influenced by environment.
Study of 433,000 people published in Chronobiology International.
