This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Non 24 hour sleep wake disorder refers to a steady
pattern of one- to two-hour delays in sleep onset and wake times in
people with normal living conditions. This occurs because
the period of the person’s sleep-wake cycle is longer than 24 hours. The
condition most commonly affects people who are blind, due to an
impaired sense of light-dark cycles. Non 24 hour sleep wake disorder
can also affect sighted people. The cause of the disorder in these cases
is incompletely understood, but studies suggest melatonin levels play a
For more information, visit GARD.