Washington, June 21 (IANS): Access to artificial light and electricity has shortened the hours of sleep humans get each night, says a study that compared traditional hunter-gatherer living conditions to a more modern setting.

"Everything we found feeds what we had predicted from laboratory or intervention studies, where researchers manipulate certain aspects of light exposure. But this is the first time we have seen this hold true in a natural setting," said lead author Horacio de la Iglesia, biology professor at the University of Washington.

The researchers compared two traditionally hunter-gatherer communities that have almost identical ethnic and sociocultural backgrounds, but differ in one key aspect - access to electricity.

They wanted to see if, all other factors aside, electricity would impact people's sleep during an average week in both the summer and winter.

They found this rare scenario in northeastern Argentina, with two Toba/Qom indigenous communities living about 50 km apart.

The first has 24-hour free access to electricity and can turn on lights at any time, while the second has no electricity, relying only on natural light.

In their usual daily routines, the community with electricity slept about an hour less than their counterparts with no electricity.

Though this study took place from 2012 to 2013, the sleep-pattern differences observed between the communities can be seen as an example of how our ancestors likely adapted their sleep behaviours as livelihoods changed and electricity became available, de la Iglesia said.

"In a way, this study presents a proxy of what happened to humanity as we moved from hunting and gathering to agriculture and eventually to our industrialised society," he said.

The research was published online in the Journal of Biological Rhythms.