Experts: if you want to stay slim — sleep without light

Researchers at North­west­ern Uni­ver­si­ty in Illi­nois have found a link between light expo­sure dur­ing sleep and obe­si­ty.

Turn off your phone, TV and lights before bed if you want to stay slim, sci­en­tists say. They tracked the data of 552 peo­ple aged 63 to 84. All vol­un­teers were asked to track expo­sure to light, includ­ing at night, for a week. To the shock of the researchers, only less than half con­sis­tent­ly had a five-hour peri­od of dark­ness.

The results showed that 40.7% of peo­ple exposed to light for five hours were obese com­pared to 26.7% in the no light group. About 17.8% in the light-exposed group had dia­betes, twice as many as in the oth­er group (9.8%). A sim­i­lar dif­fer­ence was found between groups when it came to the inci­dence of hyper­ten­sion.

The dif­fer­ences were sig­nif­i­cant when oth­er poten­tial risk fac­tors were con­trolled for. The study was obser­va­tion­al, mean­ing the team was unable to prove that light expo­sure caus­es obe­si­ty, dia­betes, or hyper­ten­sion. How­ev­er, experts believe that falling asleep with the lights on can reset the bio­log­i­cal clock. This can lead to dis­rup­tion of hor­mone lev­els that have a domi­no effect and cause peo­ple to con­sume more food.

While the study only looked at old­er adults, pre­vi­ous stud­ies have shown sim­i­lar effects in younger gen­er­a­tions.

But oth­er experts argue that the light emit­ted by smart­phones and tablets is much weak­er than nat­ur­al light at dawn. They say that the prob­lem is relat­ed to the increased activ­i­ty of peo­ple who use gad­gets before bed or instead of sleep.