Synergistic impact of diabetes and cognitive impairment

IntroductionDiabetes mellitus (DM) is increasing globally in both prevalence and population size as a common metabolic disease, especially in China (1). Epidemiological studies have reported that DM is associated with an increased risk of cause-specific mortality (2–4). However, much less information is available in China. Additionally, there are few studies on the impact of DM on mortality risk for Chinese older adults living in the community, which deserves further study.Cognitive impairment (CI) is a highly prevalent mental disorder in older adults and is considered an intermediate transitional stage between cognitively normal and dementia (5). China is one of the countries with the fastest aging worldwide, the prevalence of CI in older adults is increasing year by year, and the number of people affected is expected to exceed 140 million by 2050 (6). A recent meta-analysis, which explored the association between CI and mortality, observed that CI detected by the Mini-Mental State Examination (MMSE) is associated with an elevated risk of all-cause mortality (7). Some studies in Western populations have also shown that individuals with CI increase cause-specific mortality (8–10). However, the link between cognitive function and cause-specific mortality risk in Chinese older adults is still lacking.Both DM and CI are long-term disabling conditions. They share a common pathological mechanism and coexist in people older than 60 years (11). Interestingly, DM is a known potentially modifiable risk factor for CI (12). There is evidence that CI is a serious complication of DM that adversely affects the brain of patients with DM; individuals with DM are twice as likely to develop dementia as those without DM (13, 14). Meanwhile, CI, as a high-risk group for dementia, has 10%–15% of patients with CI progress to dementia per year, and DM can accelerate the transformation rate by 1.5–3.0 times (15). However, the control of DM is no longer a traditional treatment but a systematic management (16, 17). CI leads to self-management difficulties and increases the risk of DM and its complications (11, 14, 18). Therefore, DM and CI form a two-way vicious circle.In addition to the vascular complications of DM itself or the risk of mortality caused by blood glucose fluctuations, CI is an important prognostic factor for the elderly with DM, and the impact on the prognosis when combined with DM is still unclear. Although the current expert consensus on diabetic cognitive dysfunction in the Chinese population has been published (19), a comprehensive examination of their associations with long-term outcomes is not available. Hence, we assessed the combined effect and multiplicative interaction of these two conditions on all-cause and cause-specific mortality in the Beijing Elderly Comprehensive Health Cohort Study (BECHCS).MethodsStudy design and populationThe BECHCS is a prospective cohort study, which was based on urban and rural areas of older adults. Study design and detailed information on the BECHCS have been reported elsewhere (20, 21). Participants who met the following criteria were included in the BECHCS. Inclusion criteria were the following: (1) aged 60 years or above who had lived in the Wanshou Road Community of Haidian District and Miyun county (≥1 year) in Beijing, (2) could understand and cooperate to complete the study evaluation, and (3) willing to take part in the physical examination and biological sample collection. The exclusion criteria were as follows: (1) those with serious diseases or functional disorders, (2) those who were unable to participate in the physical examination and evaluation items, and (3) those with suspected dementia (MMSE score
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