Diabetes mellitus (DM) is a group of metabolic disorders characterized by elevated levels of glucose in the blood resulting from defects in insulin secretion, insulin action, or both (1). The burden of DM is increasing worldwide, especially in developing countries (2). In 2014, the global prevalence of diabetes was 422 million, and by 2040, this number is expected to rise to more than 642 million. The healthcare costs for DM reached 162 billion dollars in 2019 and will be 185 billion dollars in 2045 (3, 4). Inappropriate management of blood sugar in patients with DM leads to micro-vascular and macro-vascular complications, subsequently leading to high morbidity and mortality rates. In addition, diabetes independently increases the occurrence of cognitive impairment (CI), which is complicated by dementia (5–7).

CI is defined as a disturbance in memory, acquiring knowledge, focusing, or making decisions that have a negative impact on activities of daily life (8). Patients with DM are more likely to develop cognitive problems and dementia than patients without DM (9). DM can lead to the accumulation of waxy protein in the neuron by decreasing its excretion through cerebrospinal fluid, ultimately resulting in cognitive decline (10). Extended exposure of nerve cells to high levels of glucose weakens the connections between neurons, leading to their distortion, a condition directly linked to cognitive dysfunction (7).

Different studies have suggested that the exact pathophysiology of CI in diabetic patients may be due to blood vessel abnormality, insulin transmission disturbance in the cerebrum, recurrent attack of nerve cells with hyperglycemia and hypoglycemia, and accumulation of waxy protein in the neuron (11, 12). The global prevalence of CI is 45% (13) with the lowest and highest prevalence being 21.8% and 67.5%, respectively (14, 15). The global prevalence of complications of CI (dementia) in 2010 was 35.6 million, which is expected to rise to 65.7 million by 2030 (16). The overall prevalence of CI in sub-Saharan African countries among the general population has been estimated to be between 6.3% and 25% (17). The comorbidity of DM and CI is the major challenge for the long-term management of DM. DM not only causes CI but also induces the complications of CI (18). The global healthcare cost of CI complicated by dementia is 1.5 times higher than that of patients without dementia (19).

An increase in the magnitude of CI with the high cost of healthcare will impose a serious social, medical, and economic burden, causing a major challenge to the already strained healthcare system of African countries. CI is a major problem that affects the effective long-term management of diabetes. Early diagnosis of CI in patients with diabetes is important for the recovery of cognitive function and the delay of cognitive decline, as well as improving medication adherence in people with diabetes. Scientific evidence on the magnitude of CI will provide a sound basis for the determination of healthcare needs and the planning of effective healthcare services.

Despite this, there are no comprehensive data on the prevalence and associated factors of CI among patients with diabetes in Africa. We therefore designed this review to assess the prevalence and associated factors of CI among patients with diabetes in Africa.

The international Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines were used (20) to report the findings of this systematic review and meta-analysis ( Supplementary Material 1 ).

According to the review, the pooled prevalence of CI among patients with diabetes in Africa is found to be 43.99% (95% CI: 30.15–57.82, p < 0.001). This result is in line with the findings of studies conducted in China, 45.0% (95% CI: 36.0–54.0) (13); India, 33.73% (37); Korea, 31.5% (38); Philippines, 45% (39); and Poland, 32.7% (40).

However, the finding is higher than the result of studies done in Japan, 26% (41); China, 21.8% (14) and China, 13.5% (42); USA, 25.6% (43); and New York, 28% (44). The elevated prevalence observed in our review could stem from several factors. First, in the setting of the aforementioned study, hospitalized patients may typically experience better plasma glucose management as physicians prioritize close monitoring of their levels, potentially leading to a lower prevalence in this group. Conversely, in our study setting, the study population tends to be of lower socioeconomic status, which is linked to poorer cognitive function due to limited resources and healthcare access. Additionally, variations in the study populations, such as the inclusion of individuals with advanced DM in the Nigerian study, may significantly contribute to the occurrence of complications and cognitive decline. Finally, the substandard quality of healthcare services in African contexts may also play a role in the higher prevalence observed. The other interesting reason for this discrepancy is that carriers of apolipoprotein E (APOE) ϵ4 are at high risk for cognitive decline and Alzheimer’s disease. The ϵ4 allele is more common in Black than white individuals. The ϵ4 allele is associated with a risk of cognitive decline and dementia (45).

However, the pooled prevalence of CI in our review is lower than the findings of studies done in India, 58.29% (46) and 64.86% (47) and Pakistan, 67.3% (15). A potential explanation could be the variation in the age demographics of the subjects studied. The research conducted in Pakistan involved older patients with DM, who are more prone to age-related cognitive decline. Conversely, studies in India focused on patients with chronic DM, who are at higher risk for various complications, including CI.

According to our analysis, the random pooled odds ratio of CI among patients with diabetes who completed primary education was 6.08 times higher as compared to those whose educational level was college or above. The finding is similar to the results of studies conducted in China and Germany (48, 49). This may be due to the fact that individuals with higher education tend to have a larger “cognitive reserve,” meaning that they have a greater capacity for mental processing and can better compensate for age-related declines in brain function. This reserve may be built through years of stimulating mental activity, including learning new information, problem solving, and engaging in complex tasks.

The random pooled odds ratio of developing CI among patients with DM whose blood glucose was uncontrolled was 5.85 times higher compared to patients with DM whose blood sugar was controlled. The finding is consistent with the results of studies done in New York and India (38, 50). This is explained by the fact that elevated blood sugar levels in diabetes can directly damage neurons through an increased polyol pathway, advanced glycation end products, protein kinase C (PKC) activation, and increased production of free radicals (highly reactive molecules that damage cells and DNA) (51).

Patients with diabetes whose age was above 60 years old were 3.83 times more likely to develop CI than patients whose age was lower than or equal to 60 years old. This is in line with the findings of a study done in India (52). The possible justification for this might be that as age increases, the brains naturally undergo changes that can contribute to cognitive decline, including neuronal loss (gradual death of neurons throughout the brain, particularly in areas critical for memory, learning, and reasoning), synaptic dysfunction (weakening of connections between neurons, hindering communication and information processing), and neuro-inflammation (chronic low-grade inflammation in the brain, which can damage neurons and impair cognitive function) (48). The other justification for this may be due to a decline in processing speed, working memory, and episodic memory (recalling specific events) with age (52). Another reason for this may be due to early-onset familial Alzheimer’s disease (EOFAD), which has some distinctive features including early age at onset, positive family history, a variety of non-cognitive neurological symptoms and signs, and a more aggressive course. There is marked phenotypic heterogeneity among different mutations in EOFAD.

The review also identified that patients with DM who had diabetes for more than 10 years were more than 1.13 times more likely to develop CI than patients with diabetes duration of less than 10 years. The finding is in line with the studies done in China, Mexico, and London (42, 53, 54). This is justified by the long duration of DM as an atherogenic factor; it may increase the risk of cognitive dysfunction through well-recognized associations with stroke, causing cerebral disease and cerebral infarction (55).

Based on our systematic review, individuals with DM exhibit a substantial prevalence rate (43.99%) of CI. CI was found to be associated with factors such as primary level of education, poorly controlled DM, age above 60 years, and diabetes duration greater than 10 years. Developing suitable risk assessment tools is crucial to address uncontrolled hyperglycemia effectively. Healthcare professionals in Africa ought to prioritize the monitoring of cognitive function in patients with DM. Early identification of CI among patients with DM is beneficial for both restoring cognitive function and slowing down cognitive decline. Healthcare institutions need to create diagnostic and treatment plans tailored to individuals with chronic diabetes to address cognitive issues, with a particular emphasis on the elderly population. Additional interventional research endeavors focused on mitigating cognitive decline in DM, particularly those targeting novel risk factors in primary care settings, are recommended.

The original contributions presented in the study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author.

WC: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. YF: Data curation, Writing – original draft. AZ: Data curation, Writing – original draft.