Alzheimer’s disease is the leading cause of dementia – a syndrome (a group of related symptoms) associated with an ongoing decline of brain functioning.
It impairs a person’s cognitive function, affecting their memory, thinking skills and other mental abilities.
Alzheimer’s disease is a progressive condition, which means the symptoms develop gradually over many years and eventually become more severe.
Most people associate Alzheimer’s with memory loss, but increased, excessive day napping may also indicate the condition.
Studies have previously made the connection between Alzheimer’s disease and excessive day napping, but now UC San Francisco scientists have provided an explanation for this phenomenon.
According to a study published in Alzheimer’s and Dementia, Alzheimer’s disease directly attacks brain regions responsible for wakefulness during the day.
The new research demonstrates that these brain regions (including the part of the brain impacted by narcolepsy) are among the first casualties of neurodegeneration in Alzheimer’s disease, and therefore that excessive daytime napping – particularly when it occurs in the absence of significant nighttime sleep problems – could serve as an early warning sign of the disease.
In addition, by associating this damage with a protein known as tau, the study adds to evidence that tau contributes more directly to the brain degeneration that drives Alzheimer’s symptoms than the more extensively studied amyloid protein.
Tau protein naturally occurs in the brain and helps brain cells communicate with each other, explained Dementia UK.
“Our work shows definitive evidence that the brain areas promoting wakefulness degenerate due to accumulation of tau – not amyloid protein – from the very earliest stages of the disease,” said study senior author Lea T. Grinberg, MD, PhD, an associate professor of neurology and pathology at the UCSF Memory and Aging Center and a member of the Global Brain Health Institute and UCSF Weill Institute for Neurosciences.
To conduct the investigation, lead author Jun Oh, a Grinberg lab research associate, and colleagues precisely measured Alzheimer’s pathology, tau protein levels and neuron numbers in three brain regions involved in promoting wakefuless from 13 deceased Alzheimer’s patients and seven healthy control subjects, which were obtained from the UCSF Neurodegenerative Disease Brain Bank.
Compared to healthy brains, Oh and colleagues found that the brains of Alzheimer’s patients had significant tau buildup in all three wakefulness-promoting brain centres they studied – the locus coeruleus (LC), lateral hypothalamic area (LHA), and tuberomammillary nucleus (TMN) – and that these regions had lost as many as 75 per cent of their neurons.
“It’s remarkable because it’s not just a single brain nucleus that’s degenerating, but the whole wakefulness-promoting network,” Oh said.
She added: “Crucially this means that the brain has no way to compensate because all of these functionally related cell types are being destroyed at the same time.”
Reflecting on the future implications, Oh said: “It seems that the wakefulness-promoting network is particularly vulnerable in Alzheimer’s disease,” Oh said. “Understanding why this is the case is something we need to follow up in future research.
“It suggests we need to be much more focused on understanding the early stages of tau accumulation in these brain areas in our ongoing search for Alzheimer’s treatments.”
According to Alzheimer’s Research UK, determining a person’s risk of developing Alzheimer’s is complicated – it is a complex combination of age, genetics and lifestyle.
But the biggest risk factor for developing late-onset Alzheimer’s is age, said the health body.
According to the NHS, Alzheimer’s disease is most common in people over the age of 65.
Alzheimer’s Research UK also noted that certain lifestyle factors associated with cardiovascular disease (like heart disease and stroke) may also raise a person’s risk of developing Alzheimer’s disease.
To keep healthy, the charity advised:
- Be active and exercise regularly
- Don’t smoke
- Eat a healthy balanced diet
- Control high blood pressure
- Keep cholesterol at a healthy level
- Maintain a healthy weight
- Only drink alcohol within recommended limits.