Sleep deprivation cripples the immune system, a new study has revealed - explaining why so many of us get sick without good rest.
Researchers at the UW Medicine Sleep Center examined 11 pairs of identical twins with different sleep patterns, taking blood samples from each.
They found overwhelmingly that the twin who got less sleep had a more depressed immune system compared with their sibling.
It is one of the first studies to employ 'real world' conditions to confirm how lack of sleep hampers white blood cells, which are essential to keep up our immunity.
'What we show is that the immune system functions best when it gets enough sleep. Seven or more hours of sleep is recommended for optimal health,' said lead author Dr. Nathaniel Watson.
The team elected to examine twins, since studies show genetics accounts for up to 55 percent of our sleep behaviors.
They focused specifically on immune response, rather than the more commonly examined factors - such as inflammation.
It builds on previous studies that show when sleep deprived people are given a vaccine, there is a lower antibody response.
Other reports have shown that sleep deprived people are far more likely than their rested peers to get the rhinovirus if they are exposed to it.
But, the researchers warn, data from the Centers for Disease Control show that Americans are now sleeping an estimated 1.5 to two hours less than they did a century ago.
About one-third of the working population sleeps less than six hours per night.
'Modern society, with its control of light, omnipresent technology and countless competing interests for time, along with the zeitgeist de-emphasizing sleep's importance, has resulted in the widespread deprioritization of sleep,' the authors wrote.
Dr Watson added: 'This study provides further evidence of sleep to overall health and well-being particularly to immune health.'