Sleep may also be a powerful modifiable risk factor in memory decline

Dear Editor,

We read with great interest the study published by Jia et al., investigating the association between a healthy lifestyle and memory decline in older adults. The authors discussed a broad range of healthy lifestyle factors in this study which provides a valuable insight into the importance of maintaining a healthy lifestyle for slowing cognitive decline. We commend their findings showing that a healthy lifestyle does slow the rate of memory decline, even in those individuals who are genetically susceptible, harbouring variants in APOE ε4. This is of particular importance given that these risk factors are modifiable and relatively easy interventions to advise patients on numerous levels; through public health messaging and in primary and secondary care settings. In addition, in patients with APOE ε4 variants, these findings offer value in showing that these individuals can also modify their risk of cognitive decline. Thus, empowering patients in how they can reduce their risk of cognitive decline even with a non-modifiable risk factor.

However, we feel that the authors overlooked one key area of a healthy lifestyle that is important to consider with respect to cognitive decline; that being sleep and sleep hygiene. Long has it been known that issues with sleep are an all-cause risk factor for cognitive decline and dementia, as reviewed eloquently by Xu et al. [1] It is an interesting lifestyle parameter to consider given that sleep deprivation and sleep issues are also associated with food desire and appetite regulation which may negatively influence healthy food choices. [2,3] Other factors may also be affected by poor sleep quality such as desire or motivation to exercise and alcohol consumption. Therefore, we think it is vital to consider sleep as a lifestyle factor, as it is a confounding variable that is likely to influence other factors investigated in this study. It should also be highlighted that sleep is also a modifiable risk factor that is an easy intervention to advise patients on with respect to emphasising the importance of getting enough sleep and sleep hygiene practises.

Providing evidence for the association with slowing cognitive decline as well as promoting more healthy behaviours such as reduced desire to consume energy-dense, nutrient poor food would be of value.

Furthermore, information about sleep quality is easy to obtain from study participants in the form of questionnaires about average hours asleep per night, sleep hygiene related questions and reporting sleep disorders. The authors do highlight the drawbacks of this style of self-reporting data collection, so measurement errors should be taken into consideration when reporting any link between sleep and cognitive decline, as already discussed.

We support the authors in their conclusions of the lifestyle factors included in their study. We believe sleep to be an important consideration when observing lifestyle-related risk factors and cognitive decline. Obtaining this information would pivotal, particularly when looking at the contribution of sleep as an individual factor but also if sleep impacts other factors in this study. Not only would this provide evidence for sleep as a modifiable risk factor in memory decline but would help elucidate how impactful sleep is on other healthy behaviours and whether it compounds their effect. The authors highlight the need for more extensive investigations of a healthy lifestyle on cognitive decline, and we believe sleep to be an essential lifestyle factor to be considered in these future studies.

1) Xu, W. et al. (2020) ‘Sleep problems and risk of all-cause cognitive decline or dementia: an updated systematic review and meta-analysis’, Journal of Neurology, Neurosurgery & Psychiatry, 91(3), pp. 236–244.

2) Greer, S.M., Goldstein, A.N. and Walker, M.P. (2013) ‘The impact of sleep deprivation on food desire in the human brain’, Nature communications, 4, p. 2259.

3) Benjamins, J.S. et al. (2021) ‘The influence of acute partial sleep deprivation on liking, choosing and consuming high- and low-energy foods’, Food Quality and Preference, 88, p. 104074.

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