You know how your brain acts when you’re tired: it’s hard to remember things and your thoughts are sluggish. Sleep deprivation strongly impairs memory and learning, and research confirms it this (though the actual mechanism causing these deficits has escaped detection). However, a recent study done on persons with sleep apnea may provides some much-needed answers as to why.
In a study conducted at the University of California, San Diego, 55 men and women with sleep apnea were studied. Blood cortisol levels were checked every two hours for 24 hours. The patients underwent sleep studies the following night and then took a battery of tests assessing cognitive function. Of particular interest was how many times they stopped breathing, as well as how often their oxygen levels dropped in response to airway obstruction. In previous studies, we have assumed that it is the drop in oxygen that is the main culprit in causing problems with learning and memory. However, in this study they found that it was elevated cortisol levels that best predicted cognitive dysfunction.
The authors point out that their study is in agreement with other studies that have demonstrated chronic exposure to elevated cortisol levels can result in impaired cognitive function. In fact, prior studies have revealed adverse effects of elevated cortisol on a brain structure called the hippocampus. The hippocampus is a structure that resides in the temporal lobe of the brain. It has long been known that it is intimately involved in acquiring information and consolidating that information into long-term memory.
Why is this important? It may explain why sleep-deprived individuals frequently exhibit poor memory and concentration abilities. We know that insomnia sufferers, and those who chronically get inadequate sleep because of life style choices, have elevated levels of stress hormones such as cortisol. These folks do not have sleep apnea or low nighttime oxygen levels, yet they frequently exhibit cognitive dysfunction similar to patients with sleep apnea. Perhaps what they have in common is elevated levels of the hormone cortisol.
It is not too far-fetched to see what they have in common is overstimulation of the adrenal gland, which produces cortisol. The common thread being stress, produced by either insufficient, or in the case of sleep apnea, fragmented sleep. It is not inconceivable that measuring cortisol levels in patients with sleep apnea and insufficient sleep may provide an important diagnostic tool. I am hopeful that this might serve as a motivator to convince people of the importance of good quality sleep. A simple lab test would be a great tool to have in convincing people of the need to take their sleep and sleep disorders seriously. I am aware that much of this is still speculative. However, if future studies related to sleep continue to demonstrate this relationship, the possibilities are exciting.