Is Alzheimer’s Disease Actually a Sleep Disorder?
Here's what you need to know about the connection between Alzheimer’s and sleep.
Posted Feb 25, 2020
Alzheimer’s disease is a form of dementia that occurs when there is a buildup of damaging toxic plaque in the brain. This amyloid plaque is essentially poison to our brain cells. Wherever amyloids accumulate, the surrounding neurons are killed off, resulting in severe cognitive decline.
The role that amyloid plaque plays in Alzheimer’s disease is well-known, but here is a paradox that has confounded scientists for decades. You would think that Alzheimer’s patients would show large accumulations of amyloid plaque in the area of the brain responsible for long-term memory storage—the hippocampus. But that’s not true. In fact, Alzheimer’s patients show the greatest amount of amyloid accumulation in the mid-region of their frontal lobe. That is an area not particularly associated with memories, but it is associated with something else—sleep. Specifically, the mid-frontal lobe is largely responsible for the generation of non-REM and slow-wave sleep.
Does this mean that Alzheimer’s is less of a memory disease and more of a sleep disease? Let’s explore in more detail.
The Link Between Sleep and Memory
No matter what age you are, sleep plays a vital role in the processing and storage of memories. When we are awake, our brain puts our newly forming memories into short-term memory storage. When we are asleep, our brain goes back through this mass of data. Any memories deemed important are transferred to long-term memory storage. Those deemed unimportant are deleted. This process of filing and storing memories is a tricky one. It can easily get contaminated if new memories are still flooding in. So our smart brains wait until we are asleep to perform this delicate work.
Because our brain does its heavy memory lifting when we are asleep, this means that when we learn new information and then are given a chance to “sleep on it,” our recall is better. For instance, one study had a group of older adults memorize a string of word pairs like tree-chair or dog-pencil. Then they were allowed a full night’s sleep and their memory for these word pairs was tested. The results indicated there was a clear link between these older adults’ quality of sleep (specifically non-REM sleep) and their memory performance. Those who experienced the least amount of non-REM during the night had the greatest memory impairments the following day. Thus, it appears that non-REM sleep plays a vital role in the transfer of information from short- to long-term memory storage.
When we get good quality sleep, our brain acts like a steel trap for our memories. But when we are sleep-deprived, our brain acts like a sieve. Important information and memories never make it to long-term storage. They slip through the cracks and are lost forever. This is the case for people of any age, but especially older adults. As a result, what on the surface looks like age-related dementia may in fact really be sleep-deprived dementia.
The Link Between Poor Sleep and Alzheimer’s Disease
Researchers at UC Berkeley wanted to examine the link between sleep and Alzheimer’s disease more directly, so they conducted the same word-pair study described above, but only included patients diagnosed with Alzheimer’s disease. Then, through the use of PET scans, they looked at each patient’s amyloid buildup to see how it correlated with sleep quality and memory performance.
Their results showed that Alzheimer’s patients with the worst memory performance were also the ones with (1) the greatest accumulation of amyloid plaque in the mid-frontal lobe and (2) the greatest decline in non-REM sleep. This finding is important because it suggests poor quality sleep may be the missing link that connects amyloid buildup to memory loss in Alzheimer’s patients. Plaque buildup in the mid-frontal lobe causes less non-REM sleep, and less non-REM sleep causes memory impairments. This means that contrary to popular opinion, Alzheimer’s may not have a direct impact on memory. Instead, Alzheimer’s may indirectly impact memory via sleep.
This discovery has huge implications for the treatment of Alzheimer’s disease. If poor sleep plays a causal role in Alzheimer’s development, then treating poor sleep may be a novel way to treat or even prevent the disease. More research is certainly needed on this topic to make clear conclusions, but a few new studies have provided promising results. For example, one study found cognitive decline among Alzheimer’s patients was significantly reduced when those patients were treated for sleep apnea. Another study found Alzheimer’s patients showed a reverse in cognitive decline when they took melatonin, a supplement used to improve sleep.
Furthermore, this discovery might also allow for early detection of the disease. By the time memory disturbances appear, Alzheimer’s disease has already progressed significantly. But sleep disturbances appear several years before the onset of Alzheimer’s. This suggests that sleep issues might serve as an early-warning detector of the disease.
Tips for Fixing Poor Sleep in Older Adults (or Any Age)
If poor sleep is an underlying cause for dementia in older adults, can the fix be as simple as taking a sleeping pill?
Unfortunately, no. Sleeping pills have been shown to be an ineffective long-term solution for sleep problems. Sleeping pills may knock you out, but they do not induce the natural, restorative type of sleep that is essential for physical and mental health. In essence, sleeping pills sedate you but they don’t actually make you sleep. So even though you are unconscious after taking them, you are still missing out on all the necessary benefits of good quality sleep.
So what other options are there?
Here are a few science-backed tips guaranteed to improve your sleep, no matter your age:
1. Get Tested for Sleep Apnea
It is estimated that 20 percent of older adults suffer from sleep apnea, but nearly 80 percent of these people go undiagnosed or are wrongly diagnosed as having dementia. If you or someone you love is suffering from insomnia, daytime fatigue, dementia, depression or anxiety, it’s a good idea to have a doctor test for sleep apnea before seeking other treatments. In most cases, your doctor will arrange to have your sleep studied in the comfort of your own home.
2. Practice Good Sleep Hygiene
When you were little, you probably had a bedtime routine that involved putting on your pajamas, brushing your teeth, and having your parents read you a story. But bedtime routines aren’t just for kids—adults need them too. If you don’t currently stick to a bedtime routine, it’s time to start. Keeping a habitual routine signals to your brain that it’s time for bed. Here are a few factors to include in your routine:
- Go to bed at the same time each night, even on weekends.
- Keep your bedroom dark, cool (60 to 67 degrees), quiet, and gadget-free.
- Do something relaxing every night before bed—take a warm bath, listen to soothing music, read a book (paper only, not electronic), or meditate.
- Only use your bedroom for sleep and sex.
- Use a white-noise machine or earplugs to reduce noises or your partner’s snoring.
- Avoid spicy or heavy meals and alcohol three hours before bedtime.
- Avoid caffeine after lunchtime.
- Limit your liquid intake two hours before bedtime to cut down on nightly bathroom visits.
3. Try Melatonin
Melatonin peaks at dusk and serves as a chemical messenger telling your brain it’s dark now and time to get sleepy. Melatonin doesn’t actually make you sleepy, but it does serve as a cue to your brain that is time to wind down.
People with sleep issues often take melatonin supplements to improve their sleep. There is little scientific evidence to support the benefit of prescription melatonin among teenagers or middle-aged adults. But a number of studies support melatonin’s benefits for older adults. One study of adults aged 55 to 80 who consumed melatonin took less time to fall asleep, reported better quality sleep, and felt more alert the next day. And another study found melatonin may prevent or slow the progression of Alzheimer’s disease by slowing the accumulation of amyloid plaque.
To boost your melatonin, try taking 1 to 2 milligrams of a high-quality melatonin supplement each night before bed. If you prefer a more natural approach, drink tart cherry juice before bed—it has been shown to naturally boost melatonin levels.
4. Use Light to Manipulate Your Circadian Rhythm
Everyone has a clock inside their brain telling them when to sleep and when to wake. This daily cycle, called a circadian rhythm, dictates when you feel drowsy and when you feel alert and it is heavily influenced by a number of factors, including the rise and fall of the sun. However, as we age, our circadian rhythm shifts. Whereas teenagers tend to stay up late and sleep in late, older adults do the opposite. Melatonin peaks earlier for older adults, which means they go to bed and wake up at an earlier time than their younger counterparts. This shift sounds harmless but it actually leads to sleep that is shorter and more fragmented.
The solution seems simple—shift older adults’ circadian rhythms so that they start later in the evening. But unfortunately, our rhythms are very stubborn to change. However, one useful tool is light. Exposure to evening light suppresses melatonin and causes people to stay up later. That’s bad for teenagers who should be going to bed earlier, but good for older adults who are trying to stay up later. To shift your circadian rhythm, you should try to get a good dose of sunlight exposure in the late afternoon/early evening hours. This will prevent you from getting sleepy too soon. Furthermore, you should try to avoid too much early sunlight exposure because that encourages you to be an early riser. Use black-out curtains in your bedroom and wear sunglasses if you go for walks in the morning.
To learn more about the ways poor sleep affects your health, I highly recommend Matthew Walker's book Why We Sleep.
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