Mild Cognitive Impairment vs. Normal Aging 

As of 2017, people aged 60 or older account for 13% of the world population, numbering about 962 million people. Due to medical, social, and technological advancements, this number is predicted to rise to 1.4 billion, 2.1 billion, and eventually 3.1 billion by the years 2030, 2050, and 2100, respectively [1]. In older individuals, cognitive frailty is a serious and widespread problem; this is defined as the occurrence of both physical frailty and cognitive decline. In a Singaporean study observing 2,375 individuals aged 55 or older without dementia or degenerative disorders, cognitive frailty was found in 10.7% of the population and was associated with more adverse health effects [2]. Mild cognitive impairment and the normal process of aging often appear similar yet are two very different phenomena. To best address cognitive impairment in early stages, it is necessary to understand the difference between it and normal aging.

Normal aging can lead to decreased visual and auditory acuity, decreased vibratory sensations, psychomotor slowing, decreased muscle bulk, and some amount of cognitive impairment. Most cognitive functions also begin to decline, although some remain intact, for example, the ability to remember previously learned routines, or procedural memory [3]. Cognitive failure starts at what can be classified as normal cognitive decline with aging, progresses to subjective cognitive impairment (if an individual complains of cognitive decline despite a normal cognitive screening test), mild cognitive impairment (MCI), and finally, dementia [4].  

Mild cognitive impairment is a condition where individuals show cognitive impairment with some impairment of instrumental activities of daily living (IADL) [5]. The risk of MCI increases with age and is higher in those with lower level of education and in men. In amnestic MCI, memory impairments predominate; in non-amnestic MCI, impairment of other cognitive functions, such as language, executive function or sensory processing, cause greater distress [5]. In a 2013 systematic review of clinic-based studies, the conversion rate from MCI to dementia (for example, Alzheimer’s Disease [AD]) ranged from 7.5% to 16.5% [6]. Consistent with other studies suggesting memory decline is the initial symptom of Alzheimer’s disease, amnestic MCI is associated with a particularly high risk of progression from MCI to AD [7]. Biological and psychological risk factors associated with the progression from MCI to AD include having the apolipoprotein ε4 genotype, an abnormal CSF τ (tau protein) level, hippocampal and medial temporal lobe atrophy, depression, diabetes, hypertension, older age, female gender, lower MMSE (mini-mental state examination) score and higher ADAS-cog (AD assessment scale – cognitive subscale) score [8].  

MCI prevention is difficult due to its various etiologies, from AD to vascular dementia to Parkinson’s Disease; however, preventing MCI, or at least progression to more serious cognitive impairment, is likely to be the best way against the onset of dementia [4]. A 2018 systematic review showed no randomized controlled trials have affirmatively stated the benefit of pharmacological interventions in the prevention of MCI. High-dose raloxifene reduced the risk of MCI but not dementia (this was rated by the reviewers as having low strength of evidence) and more adverse events were reported after administration of estrogen and estrogen-progestin (these reports were considered inconsistent across the studies included in the review) [9]. 

Although there was insufficient evidence to support physical activity having a contributing factor towards preventing MCI, it is still recommended because the benefits may help to prevent or manage other clinical symptoms [4, 10]. After analyzing over 30 large studies, researchers concluded short-term interventions begun after years of high-risk behavior were largely insufficient to prevent MCI or dementia onset. If regular physical activity and cognitive training were to begin at an earlier age pre-emptively, the outcomes may change [10].  

More studies are needed to determine the most effective methods of preventing and/or treating MCI. In the meantime, lifestyle changes such as diet and physical activity as well as cognitive training [11] should be encouraged to promote successful and healthy aging.  

References  

1. United Nations DoEaSA, Population Division (2017). World Population Prospects: the 2017 Revision, Key Findings and Advance Tables. 2017. https://esa.un.org/unpd/wpp/publications/Files/WPP2017_KeyFindings.pdf.  

2. Feng, L., Zin Nyunt, M. S., Gao, Q., Feng, L., Yap, K. B., & Ng, T.-P. (2017). Cognitive Frailty and Adverse Health Outcomes: Findings from the Singapore Longitudinal Ageing Studies (SLAS). Journal of the American Medical Directors Association, 18(3), 252–258. https://doi.org/10.1016/j.jamda.2016.09.015  

3. Hazzard, WR, Halter, JB. Hazzard’s Geriatric Medicine and Gerontology. 6th ed. New York, NY: McGraw-Hill; 2009.  

4. Jongsiriyanyong, S., & Limpawattana, P. (2018). Mild Cognitive Impairment in Clinical Practice: A review article. American Journal of Alzheimer’s Disease & Other Dementias, 33(8), 500–507. https://doi.org/10.1177/1533317518791401  

5. Petersen, R. C., Lopez, O., Armstrong, M. J., Getchius, T. S. D., Ganguli, M., Gloss, D., Gronseth, G. S., Marson, D., Pringsheim, T., Day, G. S., Sager, M., Stevens, J., & Rae-Grant, A. (2018). Practice Guideline Update Summary: Mild Cognitive Impairment: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology, 90(3), 126–135. https://doi.org/10.1212/WNL.0000000000004826  

6. Cheng, Y.-W., Chen, T.-F., & Chiu, M.-J. (2017). From Mild Cognitive Impairment to Subjective Cognitive Decline: Conceptual and Methodological Evolution. Neuropsychiatric Disease and Treatment, 13, 491–498. https://doi.org/10.2147/NDT.S123428  

7. Busse, A., Hensel, A., Gühne, U., Angermeyer, M. C., & Riedel-Heller, S. G. (2006). Mild Cognitive Impairment: Long-term Course of Four Clinical Subtypes. Neurology, 67(12), 2176–2185. https://doi.org/10.1212/01.wnl.0000249117.23318.e1  

8. Li, J.-Q., Tan, L., Wang, H.-F., Tan, M.-S., Tan, L., Xu, W., Zhao, Q.-F., Wang, J., Jiang, T., & Yu, J.-T. (2016). Risk Factors for Predicting Progression from Mild Cognitive Impairment to Alzheimer’s Disease: A Systematic Review and Meta-analysis of Cohort Studies. Journal of Neurology, Neurosurgery & Psychiatry, 87(5), 476–484. https://doi.org/10.1136/jnnp-2014-310095  

9. Fink, H. A., Jutkowitz, E., McCarten, J. R., Hemmy, L. S., Butler, M., Davila, H., Ratner, E., Calvert, C., Barclay, T. R., Brasure, M., Nelson, V. A., & Kane, R. L. (2018). Pharmacologic Interventions to Prevent Cognitive Decline, Mild Cognitive Impairment, and Clinical Alzheimer-type Dementia. Annals of Internal Medicine, 168(1), 39–51. https://doi.org/10.7326/M17-1529  

10. Brasure, M., Desai, P., Davila, H., Nelson, V. A., Calvert, C., Jutkowitz, E., Butler, M., Fink, H. A., Ratner, E., Hemmy, L. S., McCarten, J. R., Barclay, T. R., & Kane, R. L. (2018). Physical Activity Interventions in Preventing Cognitive Decline and Alzheimer-type Dementia. Annals of Internal Medicine, 168(1), 30–38. https://doi.org/10.7326/M17-1528  

11. Butler, M., McCreedy, E., Nelson, V. A., Desai, P., Ratner, E., Fink, H. A., Hemmy, L. S., McCarten, J. R., Barclay, T. R., Brasure, M., Davila, H., & Kane, R. L. (2018). Does Cognitive Training Prevent Cognitive Decline? Annals of Internal Medicine, 168(1), 63–68. https://doi.org/10.7326/M17-1531