In this study among members of the MUPAC, comprising a population of urban community-dwelling older adults in Cameroon, the prevalence of severe cognitive decline was estimated at 3.9%. Despite the limitations of this study, this finding is in line with prevalence data for MNCD reported in other studies from Sub-Saharan Africa [23]. There is a paucity of research data reporting the prevalence of severe cognitive decline or dementia in Sub-Saharan Africa, with the result that it is difficult to establish an accurate picture of the situation in each individual country [6, 23–25]. Studies from Africa have generally reported heterogeneous, but usually lower prevalence of dementia than studies from Europe or America. However, the limitations of many African studies include the low quality of the methodology, varying types of study settings (i.e. in-patients, outpatients, nursing homes, and autopsy studies), and limited coverage of the different African regions.
In a report published in 2017, using the DSM-III/IV criteria and based on a total of 10 studies, experts from Alzheimer’s Disease International estimated the prevalence of MNCD in Sub-Saharan Africa to be 5.5% in persons aged 60 years and older, with a female predominance (the prevalence among women being twofold that in men of the same age) [26]. In a systematic review of the literature published in 2014 investigating the prevalence of dementia in Sub-Saharan Africa, Lekoubou et al analysed a total of 49 studies and found a prevalence of 9% [27]. In another study performed in the hospital setting in Cameroon, Kuate Tegueu et al estimated that the prevalence of severe cognitive disorders was 12% in patients aged 65 years and older. Our study provides complementary insights to the existing literature from Sub-Saharan Africa, by including urban community-dwelling adults, and by estimating the prevalence of moderate to severe cognitive decline, defined by an MMSE score < 18. We observed in our study that the rate of severe cognitive decline increased in line with age, to reach 11% in those aged 75 years and older. This is congruent with the literature [6].
In our study, we also observed an association between the level of education and cognitive performance, whereby a lower level of education was association with lower cognitive performance. This result is also in line with the large body of evidence coming from studies in high- and middle-income countries, and also from Sub-Saharan Africa. Indeed, Lekoubou et al also showed that one of the most consistent risk factors for dementia among older adults in Sub-Saharan Africa was having fewer than 6 years of education [27]. This is all the more pertinent considering that improvements in educational level have contributed to promoting healthy ageing [28]. Several potential mechanisms have been proposed to explain this link between education and the risk of dementia. It is now known that the level of education may play a protective role against neurodegeneration, promoting enhanced function of the neuronal system (whereby, when neurons die, others can perform similar functional tasks), thereby mitigating the signs of functional and cognitive deficiency [29]. For example, in the Personnes Agées Quid (PAQUID) cohort, individuals who had not completed primary school showed more rapid declines in measures of verbal fluency, psychomotor speed and episodic memory, compared with those who had completed primary school. It has further been shown that the first signs of cognitive decline appear up to 15 years before the onset of clinical disease [30, 31]. A second factor identified in our study as being related to cognitive function was BMI. In our study, low BMI was associated with lower cognitive performance. This has also been reported in other works [32, 33]. In a systematic review and meta-analysis of prospective studies, Yi Qu et al confirmed that overweight and obesity were positively associated with dementia in middle-aged adults, but negatively associated with dementia in older adults, and with cognitive disorders in both middle-aged and older adults [34]. Weight loss may result from pre-dementia apathy, or reduced olfactive function [35, 36]. Cova et al also reported in a prospective study that higher BMI was associated with a lower risk of progression to dementia and Alzheimer’s disease in patients with mild cognitive impairment, while low body weight was associated with 2.5-fold risk of progression to dementia within 2.4 years [40,41]. Our results provide a good opportunity to underline the utility of performing systematic evaluation of BMI (as a proxy of undernutrition) during home visits and primary care consultations, either by GPs or nurses. BMI can have a deleterious influence on cognitive status, and therefore, early management is essential, especially considering that BMI is often underdiagnosed in older adults. BMI is an effective, user-friendly metric that is easy to implement in routine practice. Furthermore, early intervention for nutritional status in older individuals, before it begins to affect cognition, is an objective that is closely aligned with the practices and goals of GPs in primary care. Regarding the link between loss of IADLs and cognitive decline, it is difficult to discern, in our study, whether the IADL impairment is the cause or the consequence of cognitive decline. Nevertheless, reduced scores on IADLs are associated with associated with lower cognitive performance, but seemingly, more as a consequence thereof. Roehr et al previously reported that the risk of dementia and Alzheimer’s disease was highest in individuals with both subjective cognitive decline and impaired IADLs [39].
Our study has some limitations, the main one being the use of the MMSE as a proxy to assess cognitive function. In the diagnostic work-up for MNCD, neuropsychological evaluation uses a battery of tests. Nevertheless, the prevalence of cognitive decline seems to be close to that reported for Sub-Saharan Africa. Some strengths of our study should also be noted. First, this is the first time that a study of this type has been conducted in the population of Cameroon and we included a relatively large sample size. Moreover, the quality of the data is reliable because the data were collected by clinicians trained in geriatric assessment. In addition, we achieved good data completeness, thereby maximizing the statistical power of the analyses.