Chronic insomnia affects about 10% of adults in developed countries and is the most common sleep disorder. Most cases are secondary insomnia resulting from a physical or mental health problem or from the effects of medication or substance abuse. However, about a quarter of people with insomnia have primary insomnia which has no other cause. A small-scale study by researchers at Harvard Medical School found that people with primary insomnia have lower levels - by about 30% - of a substance called gamma-aminobutyric acid (GABA) in their brains. GABA decreases overall brain activity in many areas helping the brain to shut down. Significant correlations were found between GABA levels and both subjective and objective sleep measures. Reductions in GABA levels have also been found in people suffering from anxiety and depression. Primary insomnia shares many features with anxiety and depression and is considered to be an important risk factor for both.
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