Dixon Yang, MD
In this focused update, Drs. Hilal and Brayne discuss the role of life course inequalities in brain health and successful aging. Brain health is defined as the development and preservation of optimal brain integrity and neural network functioning for a given age [1]. Sustained brain health over a lifespan is important in the maintenance of an individual’s ability and independence. Poor brain health may manifest as cognitive impairment or stroke in later life. Especially as the proportion of the older population increases worldwide, maintaining brain health will likely become a growing public health challenge. In this article, the authors outline the epidemiological trends and social determinants of health that underpin healthy brain aging. As many of these trends start early in life, Drs. Hilal and Brayne discuss possible mechanisms for healthy brain aging and opportunities for research and societal approaches towards promoting brain health across the lifespan.
Studies on epidemiological trends of age-related cognitive impairment and stroke in high-income countries have shown age-specific incidence of dementia and stroke are lower in generations during which there is a societal investment towards early life protection. This may include population-wide measures such as rising access to education, early vaccination programs, and increased access to healthcare [2,3]. Growing evidence also suggests cumulative exposure to vascular risk factors throughout life, even in utero and across generations, increases the risk of dementia and stroke [1]. For social determinants of health, early life poverty, low living standards, and adverse childhood experiences such as parental separation or low education are associated with poor long-term brain health and low life expectancy [4]. The World Health Organization estimates that 30% of poor brain health could be attributed to early adverse social determinants of health [5]. Therefore, consideration of early life course experiences is important in the maintenance of aging brain health.
The authors discuss how these life course adverse factors affect the preservation of plasticity, resistance, resilience, and reserve which make up brain health. Plasticity is the nervous systems’ ability to adapt to changing internal and external demands. Resistance refers to an individuals’ ability to demonstrate lower than expected levels of brain injury based on individual characteristics, while resilience is the individuals’ ability to function at higher cognitive levels than expected based on injury. Reserve indicates the premorbid capacity for injury before onset of disease. Negative factors across the lifespan may affect these characteristics of brain health, potentially manifesting in later life as dementia or stroke (Figure). While there has been increasing focus on identifying preclinical markers for dementia and stroke, the authors argue a broader approach is needed that considers cumulative lifespan risk and includes contextual factors such as social determinants of health, instead of simply controlling for statistically. Public health measures may seek to reduce these life course inequalities in an effort to promote brain health.
References:
- Gorelick PB, Furie KL, Iadecola C, et al; American Heart Association/American Stroke Association. Defining optimal brain health in adults: a presidential advisory form the American Heart Association/American Stroke Association. Stroke 2017;48:e284-e303.
- Matthews FE, Arthur A, Barnes LE, et al; Medical Research Council Cognitive Function and Ageing Collaboration. A two-decade comparison of prevalence of dementia in individuals aged 65 years and older from geographical areas of England: results of the Cognitive Function and Ageing Study I and II. Lancet 2013;382:1405-1412.
- Wolters FJ, Chibnik LB, Waziry R, et al. Twenty-seven-year time trends in dementia incidence in Europe and the United States: the Alzheimer Cohorts Consortium. Neurology 2020;95:e519–e531.
- Asmussen K, Drayton E, Fischer F, McBride T. Adverse childhood experiences: what we know, what we don’t know, and what should happen next. Early intervention foundation 2020:129.
- Kessler RC, McLaughlin KA, Green JG, et al. Childhood adversities and adult psychopathology in the WHO World Mental Health Surveys. Br J Psychiatry 2010;197:378–385.
