Dementia: Risk factors

Original Editor - lucinda hampton

Top Contributors - Lucinda hampton  

Introduction[edit | edit source]

Dementia risk factors can be categorised into modifiable and non-modifiable risk factors. Modifiable risk factors include physical inactivity, tobacco use, unhealthy diets and harmful use of alcohol. Further, certain medical conditions are associated with an increased risk of developing dementia, including hypertension, diabetes, hypercholesterolemia, obesity and depression. Other potentially modifiable risk factors may include social isolation and cognitive inactivity. Non-modifiable risk factors for dementia include age and genetics. Age is the primary risk factor for dementia, although it is not a consequence of ageing while genetics can also increase risk.

ANU Alzheimer's Disease Risk Index[edit | edit source]

ANU Alzheimer's Disease Risk Index (ANU-ADRI) is an evidence-based, validated, tool aimed at assessing an individual's exposure to risk factors known to be associated with an increased risk of developing Alzheimer's disease in late-life(> 60 years)

  1. Diabetes mellitus:is a major vascular risk factor for developing dementia through mechanisms such as glucose-mediated toxicity which causes microvascular abnormalities and neurodegeneration[1]; also, evidence of impaired insulin receptor activation in Alzheimer’s disease [2] has led to suggestions that it might represent an insulin-resistant brain state.[3] It has been shown from several studies that the presence of type 2 diabetes in midlife is associated with increased risk of dementia, alzheimer’s disease, vascular dementia and cognitive impairment. Dementia risk with diabetes is further increased with longer duration and greater severity of diabetes. In a review of relevant studies, it was found that diabetes was associated with a 47% increased risk of any dementia, a 39% increased risk of Alzheimer’s disease, and a 138% increased risk of vascular dementia.[4]
  2. Physical inactivity: Exercising more in midlife is associated with a reduced risk of dementia.[5] Exercise is postulated to have a neuroprotective effect, potentially through promoting release of brain-derived neurotrophic factor (BDNF),[6][7] reducing cortisol, and reducing vascular risk. However, exercise alone does not seem to improve cognition in healthy older adults.[8] Report from a meta-analysis[9] of 15 prospective cohort studies showed that physical activity had a significant protective effect against cognitive decline, with high levels of exercise being the most protective. In a study[10] looking at the impact of physical activity on different brain structures in 120 older adults assigned to either a moderate-intensity walking group or a stretching and toning group. In over a year, the stretching and toning group showed an age-appropriate reduction in the volume of their hippocampal region while the walking group showed an increase in the volume of their hippocampal region. This evidence demonstrates that increased physical activity can result in the growth of certain areas of the brain. The researchers also reported a significant increase in the memory function of the walking group.
  3. Depression: Depression doubles as a risk factor and a symptom of dementia. It is biologically probable that depression increases dementia risk as it affects stress hormones, neuronal growth factors, and hippocampal volume.[11] Cohort studies[12] with extended follow-up times show a link between number of depressive episodes and risk of dementia, which further reinforces the assertion that depression is a risk factor for dementia. However, a cohort study[13] suggests that midlife depression is not a risk factor for dementia.
  4. Smoking: Smoking is believed to be associated with dementia and cognitive decline[14] due to its effect on cardiovascular pathology. A meta-analysis[15] has shown that current smoking increased the risk of dementia (from any cause) by a significant amount (34% for every 20 cigarettes consumed per day). However, former smokers were found to have a similar risk profile to those who had never smoked. This suggests that by giving up smoking, individuals can potentially reduce their dementia risk to that of someone who has never smoked.
  5. Midlife Hypertension: has also been associated with increased risk of dementia in late life[16].
  6. Midlife obesity: is also linked to an increased risk of cardiovascular disease, vascular dementia, and Alzheimer's disease. This has been shown from a recent systematic review and meta-analysis of observational studies conducted on about 600 000 individuals. Result showed that obesity (but not overweight) at mid-life increases the risk of dementia (RR = 1.33; 95% CI: 1.08–1.63)[17]
  7. Low educational attainment: Education has been related to lower dementia risk as it appears to protect the brain from cognitive decline. A study by Roe et al 2008[18] showed completing more years of education provides protection from the emergence of the cognitive symptoms of Alzheimer’s disease. The concept of cognitive reserve describes how education and cognitive stimulating may lower cognitive impairment.
  8. Hearing loss: it has also been associated with an increased risk for dementia or cognitive decline.[19] A recent meta-analysis of prospective cohort studies showed that the relative risk of hearing impairment on incident Alzheimer’s and MCI was 2.82 (95% CI: 1.47–5.42)[20]. In addition, a meta-analysis published by the Lancet Commission showed that hearing loss can almost double the risk of incident dementia (RR = 1.94, 95% CI: 1.38–2.73)[21]
  9. Social Isolation: Social disengagement has been shown to increase risk of cognitive impairment and dementia in older individuals[22]. A systematic review and meta-analysis of longitudinal cohort studies showed that lower social participation, less frequent social contact and loneliness were associated with higher rates of incident dementia.[23]

References[edit | edit source]

  1. Qiu C, Sigurdsson S, Zhang Q, et al. Diabetes, markers of brain pathology and cognitive function: the Age, Gene/Environment Susceptibility-Reykjavik Study. Ann Neurol 2014; 75: 138–46. 74
  2. Frölich L, Blum-Degen D, Bernstein HG, et al. Brain insulin and insulin receptors in aging and sporadic Alzheimer’s disease. J Neural Transm (Vienna) 1998; 105: 423–38.
  3. Biessels GJ, Staekenborg S, Brunner E, Brayne C, Scheltens P. Risk of dementia in diabetes mellitus: a systematic review. Lancet Neurol 2006; 5: 64–74
  4. Lu FP, Lin KP, Kuo HK. Diabetes and the risk of multi-system aging phenotypes: a systematic review and meta-analysis. 2009,4(1)
  5. Andel R, Crowe M, Pedersen NL, Fratiglioni L, Johansson B, Gatz M. Physical exercise at midlife and risk of dementia three decades later: a population-based study of Swedish twins. J Gerontol A Biol Sci Med Sci 2008; 63: 62–66.
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  8. Young J, Angevaren M, Rusted J, Tabet N. Aerobic exercise to improve cognitive function in older people without known cognitive impairment. Cochrane Database Syst Rev 2015; 4: CD005381.
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  18. Catherine M. Roe, Mark A. Mintun, Gina D’Angelo, Chengjie Xiong, Elizabeth A. Grant, John C. Morris. Variation of Education Effect With Carbon 11–Labeled Pittsburgh Compound B Uptake. Arch Neurol. 2008;65(11):1467-1471
  19. Lin FR, Yaffe K, Xia J, Xue QL, Harris TB, Purchase-Helzner E et al. Hearing loss and cognitive decline in older adults. JAMA Internal Medicine.(2013) 173(4):293–299.
  20. Zheng Y, Fan S, Liao W, Fang W, Xiao S, Liu J . Hearing impairment and risk of Alzheimer’s disease: a meta-analysis of prospective cohort studies. Neurological Sciences.(2017) 38(2):233–239
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