What causes Alzheimer’s and cognitive decline? That’s a loaded question, as many things likely contribute to these disorders. A signature marker of impending Alzheimer’s is a brain build up of a residue called amyloid beta. This residue is always present in the brain, but as cognitive decline sets in, the mechanisms that typically clear out the amyloid begin to malfunction. Small “plaques” are formed from the aggregated residue, and these plaques begin to interfere with brain functioning. It has been previously reported that sleep acts as a type of cleaning system that removes unwanted junk from the brain. So might sleep help with the clearing of plaques? If so, poor sleep would likely predict a plaque build-up.
To test this question, a group of 13 older adults with and without existing cognitive decline were studied. Each underwent a full night sleep study and also brain imaging. This imaging is able to show any areas of the brain that have amyloid build up. Within each group of participants, sleep variables associated with sleep apnea (apnea hypopnea index/AHI and blood oxygen levels) were measured.
Results showed that in those who had Mild Cognitive Impairment (the precursor to Alzheimer’s, diagnosed via neurocognitive testing), there was a relationship between amyloid build up and AHI/blood oxygen levels during sleep. The amyloid build up was seen in an important brain area – the precuneus – which is often affected in those with Alzheimer’s. Interestingly, in those who did not have Mild Cognitive Decline, this relationship did not exist.
Overall, it is important to remember that this study took place in a very small sample of 13 older adults. What’s more, this group of 13 had to be divided in two to compare those with Mild Cognitive Decline to those without. In the world of neuroimaging, this is a very, very small sample. However, it is important to consider the implications of these results if they do indeed hold with a larger population. Given that sleep acts like a waste-removal system, it may be that sleep helps clear excess amyloid from the brain. In this sample, because untreated sleep apnea was present, it seems that sleep was disrupted and could not do its cleaning job. Confusingly, though, in those without cognitive decline, sleep apnea did not seem to be as important. Clearly, a follow-up study is necessary, and a larger sample is needed. For the time being, trust that sleep apnea is indeed damaging to cognitive decline, and stay treated!
Spira, A. P., Yager, C., Brandt, J., Smith, G. S., Zhou, Y., Mathur, A., ... & Wu, M. N. (2014). Objectively measured sleep and β-amyloid burden in older adults: A pilot study. SAGE Open Medicine, 2, 2050312114546520.