A study which was published in the April, 2012 edition of the journal Sleep provides clear evidence of a strong association between symptoms of sleep apnea – i.e. snorting, gasping, breathing interruptions, etc. – and depression. The government-sponsored study involved nearly 10,000 U.S. adults who took part in the National Health and Nutrition Examination Survey, or NHANES, between 2005 and 2008. Among other things, the study participants who were not using CPAP machines were asked whether (and how often) they snorted, gasped or had interrupted breathing during sleep – that is, whether they had symptoms of obstructive sleep apnea (OSA). Men and women who reported OSA symptoms at least five nights per week were three times more likely to display signs of major depression. Previous studies have also shown an association between OSA symptoms and depression; however, this is the first study to include a nationally representative sample of U.S. adults.
Correlation or Causation
This study more or less conclusively demonstrates an association between OSA symptoms and depression; but the key question which remains is precisely what type of association is being identified. Does sleep apnea lead to (or cause) depression? Or are those who possess OSA more likely to develop depression for other reasons? Unfortunately, the NHANES study doesn’t resolve this question, and so researchers can only speculate. And it seems unlikely that a definitive answer will be determined in the near future, because such a determination would require a lengthy (and therefore expensive) study which followed individuals and recorded their behavior over the course of many years. For this reason, the supposition that sleep apnea has a causal role in producing depression will probably remain unconfirmed for quite a while.