With everyone tracking their sleep these days with Oura rings or Fitbits, there is an increased awareness about how the amount of deep, slow-wave sleep affects your overall sleep quality. Adenosine is key to slow-wave sleep, and the rate at which you break down adenosine impacts your sleep quality. BDNF, a brain-derived neurotrophic factor, is also important here.
Why is slow-wave sleep important?When you sleep, your brain goes through different electrical wave patterns. Part of the time, you will have REM sleep, which is characterized by rapid eye movement and higher frequency brain waves. Non-REM sleep cycles include brain activity at lower frequencies. Non-REM slow-wave sleep is important for memory consolidation. When you are awake, memories are stored temporarily in the hippocampus, but during non-REM slow-wave sleep, those memories are transferred to the neocortex for long-term storage.[ref] Non-REM sleep has 3 stages:
- Stage 1 is the beginning of sleep - just when you are drifting off.
- Stage 2 is a lighter stage of sleep- easy to be woken up
- Stage 3 is the deep, slow-wave sleep
Adenosine and Slow Wave Sleep:Sleep is thought to be initiated by two different processes: circadian rhythm (24-hour, built-in clock) and homeostatic sleep drive. The homeostatic sleep drive is what makes you feel sleepy, and adenosine is a key player here. Adenosine builds up in your brain during the day due to your brain using ATP (adenosine triphosphate) for energy. The ATP molecule gives up a phosphate as a way to produce energy from the chemical bond. This then creates ADT (adenosine diphosphate) which can then give up another phosphate to become AMP (adenosine monophosphate). The final step leaves the cell with just adenosine. As the adenosine builds up, it drives you towards needing to sleep. The adenosine receptor, ADORA2A, is what adenosine attaches to and plays a crucial role in the homeostatic sleep drive. If you block the adenosine receptor, you will feel more alert. This is how caffeine works - it attaches to ADORA2A, blocking adenosine from the receptor.
Adenosine levels drop as you sleep:One way that the body can control adenosine levels is to convert them to inosine using the enzyme adenosine deaminase (ADA). This enzyme is used in the brain to decrease adenosine levels as you sleep.[ref] As the adenosine levels drop over the course of the night, the pressure to sleep also decreases.[ref] While researchers have known for a while that adenosine is important in feeling sleepy, recent animal studies have clearly shown that activation of the adenosine receptor, ADORA2A, by the adenosine molecule induces slow-wave sleep.[ref]
BDNF and Sleep:BDNF (brain-derived neurotrophic factor) acts within the brain to potentiate or increase, synaptic connections between neurons. One of the roles of BDNF is to help with neuroplasticity and memory formation. It turns out that BDNF may also be important in slow-wave sleep. Low BDNF levels have links to sleep disturbances and to an increased risk of depression.[ref]
We are all unique...A common BDNF genetic variant, known as Val 66Met (below), is linked to alterations in slow-wave sleep. A recent study showed that Val/Val carriers average 20 minutes deeper slow-wave sleep than people with a Met allele. Val/Val carriers also have higher average BDNF levels.[ref] There is a genetic variant in the adenosine deaminase (ADA) gene that decreases the clearance rate of adenosine. People who carry the variant get more slow-wave, deep sleep at night on average. The flip side is that a short night's sleep may leave them feeling groggy the next day.
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