The reason why some heavy smokers experience sadness after quitting has been demystified in a new study.
Researchers at the Centre for Addiction and Mental Health (CAMH) have shown that early withdrawal leads to an increase in the mood-related brain protein monoamine oxidase A (MAO-A).
The finding may also explain why heavy smokers are at high risk for clinical depression.
Using an advanced brain imaging method, a team led by senior scientist Dr. Jeffrey Meyer discovered that MAO-A levels in the brain regions that control mood rose by 25 per cent eight hours after withdrawal from heavy cigarette smoking.
These levels were much higher than in a comparison group of non-smoking study participants.
All 48 participants filled out questionnaires, and smokers with high brain MAO-A levels during withdrawal also reported greater feelings of sadness.
"Understanding sadness during cigarette withdrawal is important because this sad mood makes it hard for people to quit, especially in the first few days. Also, heavy cigarette smoking is strongly associated with clinical depression," said Dr. Meyer.
"This is the first time MAO-A, a brain protein known to be elevated in clinical depression has been studied during cigarette withdrawal," he added.
MAO-A 'eats up' chemicals in the brain, such as serotonin, that help maintain a normal mood.
When MAO-A levels are higher as in early cigarette withdrawal, it means that this removal process is overly active, making people feel sad.
A specific substance in cigarette smoke, called harman, may be responsible for these changes, the researchers note.
The finding was published in the Archives of General Psychiatry.