Lack of sleep has a potentially harmful effect on gene expression, according to a study out Tuesday that sheds light on the link between sleep deficits and a wide range of health conditions.

A sleep deficit -- even just a week's worth -- can have damaging effects on our genes, researchers said in a new study out Tuesday.

Lack of adequate shut-eye had already been linked to conditions from heart disease and cognitive impairment to obesity.

But sleep researcher Derk-Jan Dijk and his fellow researchers have delved into the molecular mechanisms behind the phenomenon, looking at how missed sleep leads to health problems.

They found that a week of sleeping six hours or less a night affects the expression of some 711 genes -- including those involved in inflammation, immunity, and stress responses.

Moreover, compared with test subjects who were allowed to sleep as long as 10 hours a night, those who lacked sleep had irregularities in their genes' circadian rhythms, experiencing a sharp reduction in the number of genes that wax and wane throughout the day and a dampened amplitude for many more.

At the end of the week, the test subjects were kept awake for 40 hours, with blood tests at regular intervals.

The research showed that, for those who had gotten adequate sleep previously, the affects of the sleep deprivation were seven times less than for those already operating under a sleep deficit.

Nearly a third of American workers -- some 40.6 million people -- average six hours or less of sleep a night, according to a 2010 study by the Centers for Disease Control and Prevention.

A normal night's sleep for healthy adults is considered to be between seven and eight hours.