Alzheimer’s disease is the most common form of dementia, affecting in France currently nearly one million people. With the aging of the population, the number of cases is expected to increase significantly in the years to come. Apart from drugs to alleviate the symptoms of the pathology, no treatment is currently available. Many research works therefore aim to improve prevention and delay the onset of the disease, by identifying risk factors and proposing interventions to reduce their impact.
In this context, sleep is one of the factors that arouses a lot of interest, with data suggesting that poor sleep could be associated with a higher risk of developing Alzheimer’s disease. This message has also been very often taken up in the media, sometimes in a rather alarmist way. Canal Détox takes stock of the state of knowledge.
Accumulation of toxic proteins
It has long been known that sleep problems are among the symptoms frequently presented by patients with Alzheimer’s disease, and this from the early stages of the disease. In recent years, a growing number of studies suggest that the relationship between sleep and Alzheimer’s disease is in fact “bidirectional”. Thus, the lesions typical of the disease accumulate in regions that control sleep, and will degrade the quality of the latter. Conversely, sleep disorders will also increase the risk of developing the disease by promoting the accumulation of toxic proteins.
Sleep disorders would therefore represent a risk factor on which it would be possible to act. Moreover, these disorders could be an early marker of the disease at the preclinical stage, before the appearance of the first cognitive disorders.
The available data are mainly based on animal models, focusing on the best characterized biomarkers of the disease: the presence of β-amyloid peptide and tau protein aggregates in the brain. Several studies have shown that sleep-deprived animals had high levels of these toxic proteins associated with Alzheimer’s. In humans, data suggest that sleep deprivation increases levels of β-amyloid peptide and tau protein in cerebrospinal fluid.
Study different aspects of sleep
In this context, part of the research is now focused on identifying the underlying mechanisms that would explain the link between sleep problems and the development of the disease.
But another problem arises: it is still difficult to say with certainty which aspects of sleep are really decisive in predicting the course of the disease. Is Alzheimer’s disease rather linked to a lack of sleep and nights that are too short, to difficulty falling asleep, or even to nights that are too fragmented? According to the scientists, it is important to learn more about this subject, in order to better direct public health messages and define relevant prevention strategies.
Among the landmark works on the subject, a 2013 study showed that people who slept on average less than 6 hours per night had higher amounts of β-amyloid protein in the brain, suggesting that a short duration of sleep would increase the risk of Alzheimer’s disease.
These results have been confirmed by epidemiological studies, carried out in particular within Inserm, showing that people who sleep little (sleep duration less than or equal to 6 hours per night) at the age of 50 or 60 have a higher long-term risk of developing dementia. These results therefore suggest that sleep duration could be an important parameter to take into account in the prevention of Alzheimer’s disease.
We can also cite studies focusing on specific disorders – such as sleep apnea or insomnia – which show an increased risk of developing cognitive problems and/or a greater vulnerability of certain brain regions to lesions typical of disease. Finally, other studies have shown that constantly ruminating on negative ideas, a phenomenon that can occur in particular at bedtime, also has a deleterious impact on the brain.
Interventions to mitigate risks?
However, far from the sensational headlines that make Alzheimer’s disease a fatality for young or poor sleepers, scientists believe that interventions are possible to modulate the risks associated with sleep problems.
For example, various studies evaluating the impact of physical activity or cognitive reserve (corresponding to the ability to resist or cope with brain alterations caused by aging or pathology) on sleep quality are in progress.
Interventions such as the practice of meditation to prevent dementia are also being studied. A pilot study conducted among expert participants, with more than 10,000 hours of meditation practice, showed that meditation has a positive effect on brain aging. This practice would allow a reduction of stress, anxiety, negative emotions and sleep problems which tend to increase with age. These results remain to be confirmed and are the subject of a European project carried out in Caen with elderly subjects.
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Text written with the support of Géraldine Rauchs, research fellow at the Physiopathology and Imaging of Neurological Disorders (PhIND) laboratory – Physiopathology and imaging of neurological diseases (Unit 1237 Inserm/Caen Normandy University/French Blood Establishment)