Both night-shift work and chronic sleep deprivation are increasingly implicated in mental and cognitive problems.
* Alzheimer's risk: Abnormal insulin levels (common in shift workers and sleep-deprived people) may increase the risk for certain neurodegenerative disorders, such as Alzheimer's disease, scientists at the University of Washington have found. Normally, insulin acts on the brain to promote learning and memory. However, insulin resistance may cause inflammation in the brain, a key process in the development of Alzheimer's.
* Learning: Proper alignment between sleep times and internal circadian time is crucial for optimal cognitive performance. And numerous recent studies show learning is enhanced if it's immediately followed by restorative sleep. In other words, students who pull all-nighters studying for an exam are doing themselves more harm than good.
* Mood: Even moderate changes in sleep times can have a big effect on mood. Diane Boivin of the Centre for Study and Treatment of Circadian Rhythms at Douglas Mental Health University Institute in Montreal published research last year in the journal Sleep showing that serotonin levels -- a key substance for mood stability -- are lower in shift workers than day workers. Other studies have found that exposure to bright light in the morning can lift the moods of people with depression, and that prescribed periods of sleep deprivation can interrupt a bout of depression.
* Bipolar disorder: Flawed circadian rhythms may be to blame for bipolar disorder. In a study published last year in the Proceedings of the National Academy of Sciences, scientists from the University of Texas Southwestern Medical Center identified a gene that, if disrupted, causes mice to behave as if they have bipolar disorder. Correcting the gene mutation could lead to a therapy for the illness, the scientists said.