Dementia Around the World and the Latin America and Mexican Scenarios

INTRODUCTION

Dementia is a syndrome characterized by a progressive deterioration of higher mental functions, leading to difficulties with language, memory, thinking, attention, abstraction, perception and other cognitive skills that affect the individual’s ability to perform everyday activities [1]. Dementia could be related to any number of diseases ranging from vascular cerebral problems, Alzheimer’s disease (AD), Parkinson’s disease, to normal pressure hydrocephalus [2–4].

AD is the most common cause of dementia, accounting for 60–80% of cases, followed by vascular dementia, dementia with Lewy bodies, mixed dementia, frontotemporal lobar dementia, and Parkinson’s disease [5].

Dementia has become a major public health concern, developing into a global epidemic and increasing distribution around the world [6]. For the year 2015, it was estimated that 47 million people were living with dementia, and by 2030, this number will likely increase to 75 million and triplicate to 135 million by 2050 [7]. The projected increases are driven by population aging which is occurring at a very rapidly rate in low- and middle-income countries. The number of new cases of dementia anticipated each year worldwide is almost 7.7 million—one new case every four seconds [6]. Unfolding this by region, it means that there are 3.6 million (46%) new cases per year in Asia, 2.3 million (31%) in Europe, 1.2 million (16%) in the Americas, and 0.5 million (7%) in Africa [6].

Prevalence of dementia has been studied by epidemiologists all over the world and the projected estimates come from several sources such as epidemiologic surveys, hospital records, and electronic medical history databases. A meta-analysis involving 157 epidemiologic studies conducted between 1980–2009 worldwide, reported a prevalence of dementia between 5–8% in those aged ≥60 years, showing an exponential growth with age, two-fold increases every five years [8]. Similar results were reported in a different worldwide meta-analysis study, with a prevalence of 4.8% and a period prevalence of 6.9% in a population ≥60 years [9].

Dementia prevalence studies from Sweden, France, Spain, United States of America, United Kingdom, and Japan have shown a constant or slightly decreased prevalence through time [10–17]. The Stockholm Study showed a prevalence of 17.5% and 17.9% for the years 1987 and 2001, respectively [10]. Population studies from Spain showed a prevalence ranging from 9.4% [11] and 8.5% [12] on adults ≥70 years, and between 5.5% [13] and 5.8% [14] on adults ≥65 years. Data from the Cognitive Function and Ageing Study in UK between 1994 and 2008 showed a prevalence ranging from 6.3% to 8.3% [15].

Data from the United States from the Health and Retirement Study from the years 2000 and 2012, showed a 25% decrease on dementia prevalence from 11.6% to 8.8% on adults ≥65 years [16]. Interestingly, years of education was associated with a lower risk for dementia, and in the USA between 2000 and 2012 the average years of education increased significantly from 11.8 years to 12.7 years. It is clear that educational attainment is associated with some of the decline in dementia prevalence; however, the role of economic, environmental, social, behavioral, and medical factors contributing to the decline is still uncertain [16].

In contrast, in Japan, studies from 1985 and 2012 showed an increment of prevalence on adults ≥64 years from 6.8% to 11.3% [17]. Lack of methodological uniformity among dementia prevalence studies and differences in diagnostic criteria could likely account for some of the differences in the literature; however, it is also becoming clear there are striking risk factors applicable to low and middle income countries and ethnic and age differences in populations diagnosed with dementia [18, 19]. The issue of income is critical for one powerful reason: potentially modifiable dementia risk factors for lower income countries like India, China, Cuba, Dominican Republic, Mexico, Peru, Puerto Rico, and Venezuela include variables where interventions can occur, like childhood education, midlife hearing loss, hypertension, obesity, smoking, depression, physical inactivity, social isolation, and diabetes [18].

THE LATIN AMERICA AND MEXICAN SCENARIOS

Latin American and Caribbean low and middle-income countries face a grim scenario in terms of dementia. The situation in Mexico is particularly difficult because there are 53.4 million people in poverty. Additionally, there is a progressive change in the pyramid population distribution, with elderly populations >65 years increasing, and the Mexican economic, health system, and social problems pose difficulties in taking care of this growing population, expected to triple to 20% by 2050 [20]. The demographic structure of Latin American and Caribbean countries (LACC) is changing rapidly compared to North American and European countries, and it is expected that the number of people with dementia in LACC will increase from 7.8 million in 2013 to over 27 million by 2050. Studies from Brazil, Cuba, Chile, Peru, and Venezuela showed a global prevalence of AD at 7.1% [21]. These analyses also revealed that prevalence of dementia doubles every 5 years from 65 years of age onwards, ranging from 2.40% in the 60–64 years of age group to 33.07% in the 90–94 years of age group [21].

Although LACC can be considered a uniform region, the rate of development in each country is different, so risk factors and social impact of dementia varies between countries. It is also important to note that reliable epidemiological data is scarce and there no clear strategies to urge the governments to establish specific dementia health policies.

Mexico is facing significant health problems, including maternal mortality (34.6 deaths per 100,000 live births), mortality in children ≤1 year and of ≤5 years of age (12.5 deaths and 15.1 per 1,000 live births, respectively), and lack of health care and impoverishing effects of health care costs in a country where 46% of the population is poor [22–25]. The elderly population in Mexico and across Latin America will be seriously affected in the next 30 years as the population grows without health care, in poverty, with gender inequality, and without support [20, 26–30].

In the last 15 years, several population-based studies have been conducted to estimate dementia prevalence in Mexico. The Health, Wellness and Aging Study (SABE) was one of the first multinational surveys in the late 1990 s to evaluate the general health of elderly adults in Mexico [26]. The National Study on Health and Aging in Mexico (ENSAEM) was created by the Health National Institute and the US National Institute on Aging, and its main objectives were to evaluate the impact of illnesses and mortality on adults 50 years and over in rural and urban areas from Mexico, showing a prevalence of 6.1% on dementia cases for the year 2003 [31]. Important contributions have been made by the 10/66 Dementia Research Group, which includes 30 research groups in 20 countries in Latin America, the Caribbean, India, Russia, China, and south east Asia. For Mexico, the 10/66 Dementia Research Group reports a prevalence of 8.6% in urban areas and 8.5% in rural areas, adjusted for sex, age, and academic level [32].

In 1986, the Mexican government implemented the National System of Health Surveys with the purpose of having a better understanding of the Mexican health situation. Unfortunately, in the beginning, elderly adults were not considered in the surveys. It was only in 2012 when the latest version of the survey, known as National Health and Nutrition Survey (ENSANUT), included elderly adults. Eight thousand eight hundred seventy-four adults aged 60 and over were interviewed to learn their main health concerns, including dementia [33].

The Mexican Health and Aging Study (MHAS), a sample of 13 million Mexicans ≥50 years, was used to estimate the prevalence and incidence of dementia and cognitive impairment without dementia (CIND) in a sample of 7,166 subjects older than 60 years [31]. Results showed a prevalence of 6.1% for dementia and 28.7% for CIND; interestingly higher educational level was protective for dementia, and diabetes, hypertension, and depression were seen at baseline in incident dementia cases. Mejia-Arango and Gutierrez [31] suggested cognition in Mexican elders likely reflects educational level, economic status, and co-morbidity with two major health problems: diabetes and hypertension.

One major problem in Mexico is the underreporting of dementia cases, partially due to lack of knowledge reported by 59% of physicians [34] that likely reflects the reporting of 150 cases of new AD in 2015 and 227 in 2017 in Mexico City, a megacity with ∼9 million people [35]. A review of death certificates in Mexico from 1980 to 2014 shows a trend to writing the diagnosis in the certificates in the last two decades [36].

It is certainly of great concern the relationship between the risk of dementia, including AD and air pollution [37–42] and the presence of iron-rich magnetic nanoparticles in the brains of Mexico City residents [40].

The recent reports of the evolving AD continuum in Mexico City residents starting in childhood [41] and the significant cognitive deficits in young adults [42] raises serious concerns about the early onset and rapid progression of AD, as described by the 2018 NIA-AA research framework [43], in the Mexican residents exposed to concentrations above the USEPA standard for both fine particulate matter and ozone. The question posed by Richly et al. [34] will most certainly apply for the millions of Mexican people with high air pollution exposures sharing other factors such as low socioeconomic status, low education, and co-morbidities: Are medical doctors prepare to deal with the dementia epidemic?; and we should add: are authorities prepare to deal with health, social, economic, education, judicial, etc., consequences?

The 2018 Latino population in the US reaches almost 59 million [44], 18.1% of the nation’s total population. Arizona, California, Colorado, Florida, Georgia, Illinois, New Jersey, New Mexico, New York, and Texas are the states with more Latinos, and Mexicans are the largest foreign-born group in the country: 25% of the 44.5 million immigrants as of 2017. Mexicans on average are more likely to be Limited English Proficient, have lower levels of education, experience poverty, and lack health insurance [45].

It is clear that aging is the greatest risk factor for AD, but other demographic factors also contribute to the increment on AD cases. One of these is the rapidly growing Latino population in the US, and Latinos are more prone to develop AD than White Non-Hispanics. Furthermore, within the Latino population there are differences on the prevalence of AD cases, and despite this, the differences are still poorly understood and controversial. The variances might be based on nationality origin such as Mexicans, South and Central America, and the Caribbean Hispanics. The AD prevalence in the Latino population has reach epidemic proportions and has become a social and economic issue. Latino community idiosyncrasy influences the decision of seeking appropriate healthcare, leading to an increase risk for development of chronic diseases that place Latinos at a higher risk of AD [46].

It is imperative to keep generating epidemiological data on dementia worldwide to improve the strategies to face all the challenges associated with dementia and AD in particular.

Air pollution control ought to be a health issue across the world and of particular importance for Latin America. Identifying key environmental factors impacting neural risk trajectories in the developing brain and monitoring cognitive performance would facilitate multidisciplinary early diagnosis and prevention of dementias in high risk young populations.

DISCLOSURE STATEMENT

The author’s disclosure is available online (https://www.j-alz.com/manuscript-disclosures/19-0177r2).