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In an era where technology, working environments and the lockdowns of the COVID-19 have made it easier than ever to exist in solitude, ageing can be an especially lonely experience.

On top of friends and family passing away, illness and disability, technology has enabled people to hide away from social interaction, even down to ordering a drink in a café. This can create a very isolated environment for older people and for those with dementia, symptoms such as memory loss can exacerbate this. Losing memory of places and people near to them can make those with dementia lose confidence for venturing out on their own. Despite many believing modern society in improving and the advances in technology such as social media are helpful, it may be marginalising those with dementia and creating an unwanted divide.

As a result, loneliness is being increasingly investigated, not just for its effect on mental health, but for its effects on the development of dementia which have been found to be very real.

A longitudinal study on humans was done that supports loneliness as a risk factor for dementia and Alzheimer’s disease (AD) development (Sundström et al., 2020). In this study, a group of over 1900 participants aged 60 years and over at baseline were given a questionnaire where they rated their loneliness with a follow-up questionnaire 20 years later to compare the participants’ perceived loneliness. Of the participants in the follow-up, 428 had developed dementia – 221 of these having AD. They concluded, after adjusting for many confounders, that loneliness was a major risk for development of dementia.

Moreover, there are also studies suggesting that loneliness actually worsens memory deficits of AD. In particular, a study done in 2017 used a model of the disease in rats to show this (Li et al., 2017). The rats were bred with a gene to induce AD and were placed into memory testing tasks before and after isolated housing. After being in an isolated environment, the rats showed a significant decrease in memory performance among the rats with AD. Although this was not a study done in humans, rodents are often used as their anatomy and physiology are very similar, making the results comparable to human cases (Bryda, 2013).

Evidence for why loneliness can negatively affect memory was seen in further studies that suggested the stress induced by social isolation may be negatively affecting the brain’s ability to consolidate memories (Phillips et al., 1991). Post-mortem samples of the hippocampus (an important brain region for declarative memory formation and consolidation i.e., memory of facts and events) in AD patients showed significantly reduced levels of BDNF (brain derived neurotrophic factor). BDNF is an important protein that helps the brain to adapt and alter connections to enable new information to be stored while maintaining healthy/strong existing connections. BDNF production can be decreased in states of stress; these studies suggest that stress is one way loneliness contributes to memory deficits.

Although the patients used in the 1991 study were not socially isolated, the conclusions of this study were supported by a later study on mice (Hsaio et al., 2014) and substantiated again by a study on humans (Salinas et al., 2017).

Hsaio et al created an experiment where mice were raised until they developed AD and had measurable memory deficits, then some were placed into housing with other mice. They noted in their paper that mice do not cope well and become stressed when isolated. Researchers saw that in the mice not isolated, the co-housing-induced improvement of memory that was accompanied by increased BDNF expression in the hippocampus. From this, it was concluded that the drop in BDNF was triggered by AD, worsened by social isolation, and consequently impacted memory formation.

Later, Salinas et al were able to reproduce this with a cohort of 3294 human participants aged over 60. In their study, they found increased BDNF levels and reduced risk for dementia when participants were provided with social and emotional support across the longitudinal study (lasting for approximately 11 years).

I recently saw a bumper sticker that perhaps has more merit to it than one would think… “On an adventure before dementia”. As comical and trivialising as this saying makes the condition, the encouragement to create strong networks of friends and integrate activity into later life can have beneficial effects on a person’s cognitive functioning. This doesn’t have to be anything extreme; no doctor is going to suggest booking your grandparents onto a skydive. But encouragement to meet with friends and family, take regular walks if able and/or find a hobby that engages the mind while providing some social interaction will put any person in good stead to prevent the onset of dementia and in turn enrich their quality of life.

References

Bryda E. C. (2013). The Mighty Mouse: the impact of rodents on advances in biomedical research. Missouri medicine. 110(3):207–211.

Hsiao, Y. H., Hung, H. C., Chen, S. H., & Gean, P. W. (2014). Social interaction rescues memory deficit in an animal model of Alzheimer's disease by increasing BDNF-dependent hippocampal neurogenesis. The Journal of neuroscience: the official journal of the Society for Neuroscience, 34(49), 16207–16219.

Li A.A., Khalil M.G., Elariny H.A., Abu-Elfotuh K. (2017). Study on social isolation as a risk factor in development of Alzheimer’s disease in rats. Brain Disord Ther. 6:230.

Phillips, H. S., Hains, J. M., Armanini, M., Laramee, G. R., Johnson, S. A., & Winslow, J. W. (1991). BDNF mRNA is decreased in the hippocampus of individuals with Alzheimer's disease. Neuron. 7(5):695–702.

Salinas J., Beiser,A., Himali J.J., Satizabal C.L., Aparicio H.J., Weinstein G., et al. (2017). Associations between social relationship measures, serum brain-derived neurotrophic factor, and risk of stroke and dementia. Alzheimer's & Dementia: Translational Research & Clinical Interventions. 3:229–237.

Sundström, A., Adolfsson, A. N., Nordin, M., & Adolfsson, R. (2020). Loneliness Increases the Risk of All-Cause Dementia and Alzheimer's Disease. The journals of gerontology, Series B.  75(5):919–926.