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Alzheimer’s Disease (AD) is a progressive and irreversible neurodegenerative brain disease that impairs thinking, memory and independence, and represents the most common cause of dementia.1,2
Dementia is an umbrella term for several diseases that are principal contributors to mental disability and the need for care in old age.1 Worldwide, up to 80% of the 55 million patients with dementia are thought to have AD.1,3
A considerable increase of affected people from 55 million in 2019 to about 78 million is expected by 2030 and more than double by 2050. Europe has the second highest prevalence worldwide with 14.1 million people affected.3
AD and other forms of dementia are a World Health Organization priority and are listed among the top 10 causes of death worldwide, ranking 2nd in high-income countries worldwide.4
It is important to note that AD is not a normal part of ageing, and older age alone is not sufficient to cause the disease.1 AD operates out of sight, slowly developing over many years causing damage to the brain.5 Short-term memory loss, forgetting recent events and conversations, or struggling to follow a series of instructions are typically the first signs of the disease. Other early symptoms include confusion, difficulty finding words, or changes in mood and personality.1 This early stage of the disease, when signs become more visible, is called mild cognitive impairment (MCI) due to AD.
In the last ten years, the terminology "MCI due to AD" has been introduced in the characterization of people presenting with some mild cognitive symptoms, which do not affect the individual's ability to carry out basic activities of daily living. In addition to the clinical and cognitive assessment that may detect MCI, a biomarker confirmation, such as at least amyloid beta accumulation in the brain is required to confirm a suspected diagnosis of MCI due to AD.2
Today we understand Alzheimer’s disease to be a continuum as it can be present for decades before it is even suspected.5 The neuropathological changes in the brain leading to synaptic dysfunction can begin up to 20 years before the first symptoms appear.1,5 Even then, it often goes undetected for far too long. People with AD and their loved ones either overlook early signs of the disease, or see them as ‘senior moments’ - just part of getting older.6
Risk Factors for Alzheimer's Disease7-13
Non-Modifiable Risk Factors
- Ageing: AD risk doubles every 5 years after age 65
- Positive family history
- Female gender
- Genetic predisposition & susceptibility (trisomy 21, rare mutations in dominantly inherited AD genes, and allele ε4 of ApoE gene in sporadic AD)
- Environmental factors
Modifiable Risk Factors
- Lifestyle, such as low physical activity, smoking, unhealthy diet, harmful alcohol use, social isolation, or cognitive inactivity
- Health conditions, such as hypertension, type 2 diabetes, heart disease, depression, dyslipidemia, hyperhomocysteinemia, hearing loss, obesity
- Others, such as lower levels of education, certain medication, traumatic brain injury, or sleep disturbance
Age, genetics, family history, and environmental factors are the so called non-modifiable risk factors of AD. While age is the most dominant risk factor for cognitive decline, AD dementia is not a natural or inevitable consequence of ageing.8 Studies have shown that a variety of modifiable risk factors, such as lifestyle-related risk factors, certain medical conditions, social isolation, and cognitive inactivity do correlate with the development of cognitive impairment.8
The existence of potentially modifiable risk factors means that prevention of dementia is possible through a public health approach, including the implementation of key interventions that delay or slow cognitive decline.9
WHAT'S NEXT
The Stages of Alzheimer's Disease
Today, we understand Alzheimer’s disease to be a continuum. By the time patients show symptoms, the underlying processes of the disease have been at work for up to 20 years.
References
1. 2021 Alzheimer's disease facts and figures. Alzheimers Dement. 2021;17(3):327-406.
2. Dubois B, Villain N, Frisoni GB, et al. Clinical diagnosis of Alzheimer's disease: recommendations of the International Working Group. Lancet Neurol. 2021;20(6):484-496.
3. World Health Organization (WHO). Global status report on the public health response to dementia. Geneva: World Health Organization; 2021. Licence: CC BY-NC-SA 3.0 IGO. www.who.int/publications/i/item/9789240033245. Accessed January, 2022.
4. World Health Organization (WHO). The top 10 causes of death. December 2020. www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death. Accessed January, 2022.
5. Jack CR Jr, Bennett DA, Blennow K, et al. NIA-AA Research Framework: Toward a biological definition of Alzheimer's disease. Alzheimers Dement. 2018;14(4):535-562.
6. Wilcox J, Duffy PR. Is it a ‘senior moment’ or early dementia? Addressing memory concerns in older patients. Current Psychiatry, 2016 May:15(5):28-40.
7. Yu JT, Xu W, Tan CC, et al. Evidence-based prevention of Alzheimer's disease: systematic review and meta-analysis of 243 observational prospective studies and 153 randomised controlled trials. J Neurol Neurosurg Psychiatry. 2020;91(11):1201-1209.
8. Frisoni GB, Molinuevo JL, Altomare D, et al. Precision prevention of Alzheimer's and other dementias: Anticipating future needs in the control of risk factors and implementation of disease-modifying therapies. Alzheimers Dement. 2020;16(10):1457-1468.
9. World Health Organization (WHO). Risk reduction of cognitive decline and dementia. WHO Guidelines. www.who.int/mental_health/neurology/dementia/guidelines_risk_reduction/en. Accessed January, 2022.
10. Corrada MM, Brookmeyer R, Paganini-Hill A, Berlau D, Kawas CH. Dementia incidence continues to increase with age in the oldest old: the 90+ study. Ann Neurol. 2010;67(1):114-121.
11. Mielke MM. Sex and Gender Differences in Alzheimer's Disease Dementia. Psychiatr Times. 2018;35(11):14-17.
12. Head E, Powell D, Gold BT, Schmitt FA. Alzheimer's Disease in Down Syndrome. Eur J Neurodegener Dis. 2012;1(3):353-364.
13. Reitz C. Dyslipidemia and the risk of Alzheimer's disease. Curr Atheroscler Rep. 2013;15(3):307.