Normally, depression frequently is thought to cause poor sleep. However, I saw via Medscape that at the 50th annual meeting of the American College of Neuropsychopharmacology, Dr. Meerlo discussed some interesting research findings. In his study, he sleep deprived rats for various lengths of time and measured their brain structure and chemical responses. One day of sleep restriction did not seem to have a dramatic effect. But when they sleep deprived them for 1 week to 1 month, they saw brain changes that looked very similar to those changes in depression.
Also, it took a surprisingly long time for the rats to recover. After one week of restricted sleep, the rats needed almost a week of normal sleep amounts before the brain changes normalized. This suggests that catching up on lost sleep during the weekends may not be sufficient.
Dr. Meerlo concluded that restricted or disrupted sleep over a prolonged period of time may be a causal factor in developing depression, not just a symptom of depression.