Reviewed by Sahil Chopra, MD, and Stacey Gunn, MD.
Research by Savit Malhotra.
Introduction
We’ve spent the last few weeks examining the impact of sleep apnea on the heart and cardiovascular system. This week, we’ll be taking a turn and starting to look at how the brain is impacted. The brain is a delicate organ, and one that we still don’t know much about. What we do know is that, as the center control for the entire body, the brain needs to be well rested in order for it to function properly. Sleep apnea can greatly reduce the quality of sleep a person gets and, in turn, impact their body as a whole. This week, we will begin our discussion by looking at how sleep apnea can contribute to dementia, and continue next week by seeing how it can lead to stroke.
What is Dementia?
Dementia is an umbrella term used to describe memory loss and the loss of certain cognitive functions (such as language and problem-solving skills). Alzheimer’s disease is the most common form of dementia, with over 7.2 million people living in the United States suffering from the disease.[1,2] Aside from Alzheimer’s disease, there are also several other types of dementia, including vascular dementia (the second most common type), dementia with Lewy bodies, frontotemporal dementia, early-onset dementia, and mixed dementia.[3] Age, genetics, smoking/alcohol use, atherosclerosis (plaque buildups in the arteries), high cholesterol, plasma homocysteine (high levels of homocysteine in the blood), diabetes, and mild cognitive impairment are all risk factors of dementia.[4] Increasingly recognized, however, is the impact that sleep apnea has on contributing to the development/progression of dementia.
With the global cost of the disease being $1.3 trillion and over 55 million people suffering worldwide, it is unfortunate that there is no cure yet.[5] This is not to say that there aren’t any treatments for the disease. There are a number of medications, such as cholinesterase inhibitors and memantine, and therapies designed to help alleviate the symptoms that people suffer because of the disease.[6] While we have yet to understand the disease fully, we do know enough to help people reduce their chances of developing the disease. Part of this includes understanding how sleep apnea can contribute to dementia and why treating it can help reduce the risk of developing dementia.
How Do the Two Worsen Each Other?
When someone is suffering from sleep apnea, they experience periodic pauses in their breathing while they sleep. These lapses in oxygen lead to hypoxia, where the tissues in the body are oxygen-deprived, including the tissue in the brain. It is hypothesized that this deprivation of oxygen to the brain tissue is what leads to dementia/dementia-like symptoms.[7] The study that hypothesized this found that about 44.8% of elderly women with sleep-disordered breathing observed developed cognitive impairment/dementia, compared to 31.1% of women without sleep-disordered breathing showed signs of cognitive impairment. Aside from the hypoxia theory, it is also believed that lack of sleep increases the levels of beta amyloid and tau in the brain, two proteins related to Alzheimer’s disease.[8] While this is more specific to sleep deprivation, and more research is needed to test if this is also true for lack of quality sleep, it does potentially help to explain why sleep apnea can lead to dementia.
Although the full bidirectional relationship has yet to be explored, we know that circadian rhythms are altered by dementia. The alteration of one’s circadian rhythm affects corresponding sleep and wake times, leading to declined brain function and cognitive impairment. In turn, dementia and dementia symptoms are worsened, and insomnia can result due to the inconsistent sleep patterns.[9] As of yet, there is no strong evidence that dementia can cause sleep apnea, although it is biologically plausible that neurodegeneration could affect respiratory control centers. We know that sleep issues are quite common in those with dementia, and that sleep apnea is among those issues and is more common in those with Alzheimer’s disease.[10] Some have even found that 40% of those with Alzheimer’s disease also have obstructive sleep apnea.[9] And while sleep apnea is often considered to be a risk factor for dementia, the reverse may or may not turn out to be true.[8] Like some of the other relationships we have discussed, conducting research on the topic is particularly difficult, as it is unethical to withhold certain treatments just for the sake of research. Nevertheless, the correlation between the two is present, and it can be said that the sleep deprivation that results from sleep apnea is related to cognitive issues and memory loss.[9]
What Happens When You Treat Sleep Apnea?
As we have discussed before, CPAP therapy remains one of the most common and effective ways to treat sleep apnea. And although CPAP is not designed to treat dementia, research has shown that there are some benefits to using CPAP to help alleviate dementia symptoms. One study found that those who used CPAP saw an improvement in both their cognitive scores and their grey matter (which is important for information processing and memory) volume in certain regions of their brain (the hippocampus, which is important for learning and memory, and the frontal lobe, important for higher-level thought).[7, 11, 12]
CPAP has also been suggested in studies to help delay the onset of dementia. One study found that, when left untreated, sleep apnea led to the onset of dementia happening 10 years earlier than in those who did not have sleep apnea. In contrast, those who used CPAP were able to push the onset of dementia back 10 years compared with those who went untreated.[13] Now, this study wasn’t randomized, so it is possible that the group choosing to use was also making other beneficial health choices in their life. Although more research is needed to definitively establish a link, the current data is quite promising.
What Should I Look Out For?
As we discussed in the previous article, the STOPBANG method remains an effective way for a person to help screen themself to see if they have sleep apnea. This test/acronym (posted below for reference) isn’t perfect, but it is still an incredibly useful tool.
- S - Snoring
- T - Tiredness during the day
- O - Obstruction (brief pause in breathing while sleeping)
- P - Pressure (high blood pressure)
- B - Body mass index of 30 or greater
- A - Age of 50+
- N - Neck circumference of greater than 16 inches (in women) or 17 inches (in men)
- G - Gender (male)
If you have three or more of the above-mentioned characteristics of sleep apnea, it is important that you see a sleep medicine doctor so that they can properly diagnose you and you can begin treatment. However, we will also mention that it is possible to have sleep apnea even with a low STOPBANG score, and so a normal score should not prevent someone from being evaluated if they are otherwise concerned.[14]
It is also important that you keep note of any early signs of dementia. Commonly, people may experience large gaps in their memory that impact their daily lives. Problem-solving skills and planning ability may also be lost, in addition to a loss of completing familiar tasks. Another early sign of dementia is confusing the time or place you are in, or having difficulty understanding visual images and your surroundings. Language, such as speaking or writing, can also be impacted, and one may find themselves misplacing items more often and having trouble tracking back those items. Judgment skills may be impacted, and a person may also start to see themselves withdraw from their daily life. Finally, a person’s mood or personality may change, becoming more depressed, anxious, confused, or upset.[15] While some of these signs are broader and hard to interpret, you should always keep note of what others are telling you as well. If you are concerned you may be experiencing early signs of dementia, you should see a neurologist, psychiatrist, or other specialist so that they can give you a proper diagnosis.
Conclusion
Although dementia is a scary and alarming disease, proper treatment can greatly help alleviate the symptoms one experiences and can even help push back the onset of the disease. It is important to fully understand all of the different ways in which dementia can occur, and part of this is by understanding that poor sleep can contribute to the development of dementia. If you are worried you may have obstructive sleep apnea or already know that you do have it, seeking treatment is the best course of action. Properly treating sleep apnea can help you get the quality sleep you need to push back the onset of dementia. It is never too late to start treatment.
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