Morning light may bring sleep forward for people who go to bed very late.

The review

1. 01

   Who took part

   Studies covered sleep that runs early or late, depression and other mental illness, and dementia. Averages in the sleep-pattern studies ran from about 15 to about 70 years.

2. 02

   What they did

   Most studies used bright light from a light box, mask or glasses, or from indoor or outdoor light, mostly on waking. Treatments in the sleep-pattern studies lasted 2 to 56 days. Other groups had dim light, no treatment or a waiting list.

3. 03

   What happened

   Morning light moved sleep about 25 minutes earlier for people whose sleep ran late. Sleep was less broken up at night, and people rated their sleep trouble lower. Evening light did not move sleep later for people whose sleep ran early; if anything, it moved sleep slightly earlier.

What the review found

1. HelpedRoutines

   People with late sleep who got morning light had their sleep about 25 minutes earlier than other groups.

   • Action: Get daylight in the morningtested

   Pooled analysis of 8 studies · vs dim or coloured light, no treatment or a waiting list · ⚠ mixes trials with other kinds of study

2. No differenceRoutines

   For people whose sleep ran early, evening light did not move sleep later than the other groups' sleep did.

   Pooled analysis of 4 studies · vs dim or red light · ⚠ mixes trials with other kinds of study

3. HelpedOther outcomes

   Sleep was less broken up at night in the light groups than in the other groups.

   Pooled analysis of 20 studies · vs dim light, placebo, no treatment or a waiting list · ⚠ mixes trials with other kinds of study

4. HelpedOther outcomes

   People in the light groups rated their sleep trouble lower than the other groups did.

   Pooled analysis of 5 studies · vs dim light, placebo, no treatment or a waiting list · they rated themselves · ⚠ mixes trials with other kinds of study

Source