Abstract
We examined the association between comorbid conditions and mild cognitive impairment (MCI) in Native Hawaiians and Pacific Islanders (NHPI) (n = 54). Cross-sectional, self-reported questionnaires were utilized to collect demographic, comorbid conditions, and MCI (via the AD8 index) data. Separate logistic regression models were conducted to investigate the relationship between comorbid conditions and MCI, adjusting for other covariates. We found significantly increased odds of MCI in those reporting high blood pressure (OR = 5.27; 95% CI: [1.36, 20.46]; p = 0.016), high cholesterol (OR = 7.30; 95% CI: [1.90, 28.14], p = 0.004), and prediabetes or borderline diabetes (OR = 4.53; 95% CI: [1.27, 16.16], p = 0.02) compared with those not reporting these respective conditions. These data show that hypertension, hypercholesterolemia, and prediabetes are associated with MCI in the NHPI community, suggesting that preventive strategies to reduce chronic conditions may also potentially slow cognitive decline in underrepresented/understudied NHPI.
Keywords
Introduction
Neurocognitive aging (NA) produces changes in the brain, impacting memory, stress, decision-making, and other cognitive processes (Harada et al., 2013; Peters, 2006). The spectrum of cognitive decline in older adults ranges from normal aging to an intermediate mild cognitive impairment (MCI) stage to dementia, predominantly due to Alzheimer's disease (AD) (Davis et al., 2018). MCI prevalence impacts 6.7–25.2% of the population, increasing with age, while dementia affects nearly 50 million people worldwide (Jongsiriyanyong & Limpawattana, 2018; WHO, 2023). Brain-related aging and health have a profound impact not only on individual physical and mental functioning but also on families and society (Allen et al., 2017; Chiao et al., 2015; Deb et al., 2017; Fillit & Hill, 2005; Vandepitte et al., 2016). Therefore, examining factors related to NA is of critical public health importance.
As critically important, substantial disparities in NA, including depression, memory, stress, dementia and AD incidence, and outcomes across racial and ethnic groups, are urgent issues necessitating attention (Corriveau et al., 2017; Gianattasio et al., 2019; Mehta & Yeo, 2017). Numerous studies have demonstrated the disproportionate burden of disease, including obesity, type II diabetes, and cardiovascular disease in the Native Hawaiian and Pacific Islander community (NHPI), a rapidly growing population in the United States (Furubayashi & Look, 2005; Karter et al., 2013; Mau et al., 2009; McEligot et al., 2010, 2012). One recent retrospective medical record review study on 598 patients, including 224 Asians, 202 Whites, 87 NHPI, and 85 Other, showed the highest MCI in NHPI (Smith et al., 2021). However, very few studies have examined MCI (Ganbat & Wu, 2021; Hermosura et al., 2020; Smith et al., 2021), and very little is known about the risk factors associated with it, such as comorbid conditions (e.g., type II diabetes and hypertension) and their relationship with MCI in the NHPI community.
A meta-analysis of 17 longitudinal cohort studies involving ≈1.7 million people concluded that diabetes mellitus increased the risk of developing AD with a relative risk (RR) of ≈1.5 (Zhang et al., 2017). Studies show that type II diabetes induces vascular and cognitive decline (memory, mood, and behavior) (Lyu et al., 2020; Zilliox et al., 2016). Additionally, a history of prehypertension and hypertension in midlife or late in life has been shown to increase dementia risk and enhance AD neuropathology (Dickstein et al., 2010; Gottesman, Albert, et al., 2017). Although research shows a link between type II diabetes, hypertension, and cardiovascular disease with cognitive impairment, no studies have yet, to our knowledge, examined the relationship between comorbid conditions and MCI in NHPI.
Therefore, we conducted a community-based participatory research (CBPR) study and investigated the relationship between chronic health conditions, including blood pressure, cholesterol, prediabetes, diabetes, and stroke with MCI among NHPI older adults residing in Southern California. We hypothesized that having high blood pressure, high cholesterol, prediabetes, diabetes, and stroke would be associated with cognitive impairment in NHPI older adults.
Methods
We conducted a chi-square analysis to investigate the relationship between comorbid conditions and MCI. Also, due to collinearity between comorbid conditions, separate logistic regression analyses were conducted to measure the association between each of the following comorbid conditions (independent variable): high blood pressure, high cholesterol, prediabetes, diabetes, and stroke with MCI (the dependent variable). Cognitive functioning was dichotomized as follows: those with an AD8 summary score of 2 or higher as MCI and those indicating a score 0–1 as normal cognitive functioning. Comorbid conditions (independent variables) were included in separate models as dichotomized variables (yes, no [ref]). Other known covariates associated with cognitive impairment were also included as independent variables and are as follows: gender (female, male [ref]), education level (more than high school and less than high school [ref]), and age (continuous). Analyses were conducted using SPSS version 28.
Results
The mean age of the sample (n = 54) was 64 years (SD ± 9). All participants identified as Native Hawaiian (24.1%) or Pacific Islander (75.9%). Table 1 indicates that most participants were female (59.3%), married or partnered (66.7%), employed (46.3%), and had a high school/GED (48.1%). The participants responded having the following chronic conditions as follows: high blood pressure (59.3%), high cholesterol (50%), prediabetes (33.3%), diabetes (31.5%), and stroke (3.7%), while 38.9% reported MCI (data not shown).
Demographic and Other Sample (n = 54) Characteristics.
Table 2 compares comorbid conditions (high blood pressure, high cholesterol, prediabetes, diabetes, and stroke) between normal cognition and MCI cognitive decline. High blood pressure, high cholesterol, and prediabetes were significantly related to MCI, with p = .010, .002, and .018, respectively, and the direction of the correlation indicated that the diagnoses of these respective conditions were associated with an increased risk of MCI. Specifically, the proportion of those with MCI compared with those with normal cognition were more likely to report high blood pressure (53.1% vs. 46.9%, p = 0.01), high cholesterol (59.3% vs. 40.7%, p = 0.002), and prediabetes (61.1% vs. 38.9%, p = 0.18).
Proportion of Comorbid Conditions Between Normal Cognition and MCI.
The multivariate association between each respective comorbid condition and MCI is shown in Table 3. For each separate model, after adjusting for covariates, comorbid conditions were associated with MCI; specifically, those reporting high blood pressure (OR = 5.27; 95% CI: [1.36, 20.46]; p = 0.016), high cholesterol levels (OR = 7.30; 95% CI: [1.90, 28.14], p = 0.004), and prediabetes or borderline diabetes (OR = 4.53; 95% CI: [1.27, 16.16], p = 0.02) were significantly associated with MCI. In all models, age was also significantly associated with MCI (p < 0.05).
The Association (Multivariable Odds Ratio, OR [95% CI]) Between Comorbid Conditions With MCI.
aModel 1 refers to the model with high blood pressure.
bModel 2 refers to the model with high cholesterol.
cModel 3 refers to the model with prediabetes or borderline diabetes.
dModel 4 refers to the model with diabetes.
eModel 5 refers to the model with stroke.
*p < 0.05.
Discussion
The current study examined the association between comorbid conditions and MCI in the NHPI population residing in Southern California. We showed that approximately half of our sample reported high blood pressure and high cholesterol, while a third reported prediabetes and diabetes. Our data indicate that high blood pressure, high cholesterol, and prediabetes are associated with declining cognitive impairment in the NHPI community. Specifically, those with high blood pressure and prediabetes had 5 times the odds of MCI compared with those not reporting high blood pressure or prediabetes, and similarly those with high cholesterol (compared with those without high cholesterol) had 7 times the odds of MCI. Our risk estimates (OR and CI) should be interpreted with caution due to our small sample size; nonetheless, the direction of association shows increased odds of MCI for those with comorbid conditions.
Our findings of the association between high blood pressure and cognitive decline in NHPI have been reported in other ethnic/racial groups (Abell et al., 2018; Gottesman, Albert et al., 2017; Skoog et al., 1996). The Whitehall II cohort study, in predominantly UK non-Hispanic Whites, showed that participants with longer exposure to hypertension (SBP ≥ 130 mmHg), during midlife, had an increased risk of dementia compared to those with shorter exposure to hypertension (HR 1.29, 95% CI 1.00, 1.66) (Abell et al., 2018). A recent meta-analysis of over 2 million individuals from 135 prospective cohort studies further supported this association, indicating a significant relationship between midlife history of hypertension and the risk of dementia. Importantly, a meta-analysis of 12 trials with 92,135 participants showed that blood pressure-lowering hypertensive medication was associated with lower dementia or cognitive impairment development compared with controls (7.0% vs 7.5%, respectively, p < 0.05) (Hughes et al., 2020). Although research shows a link between hypertension and cognitive impairment, awareness and management of these comorbid conditions are still lacking in the NHPI community, which is a vulnerable and at-risk group.
Studies on the relationship between elevated cholesterol and cognitive decline are equivocal. Sáiz-Vazquez and colleagues (2020) conducted a meta-meta-analysis on 100 primary studies and five meta-analyses showing an association between only low-density lipoprotein (LDL) with AD, and no effects of high-density lipoproteins, total cholesterol, or triglycerides on AD. The biological plausibility of the influence of cholesterol on cognitive decline shows that increased LDL has vascular and neurotoxic effects (Nagga et al., 2018; Versmissen et al., 2011; Whitmer et al., 2005). We demonstrated an association between high cholesterol and MCI in NHPI; however, we only queried on total cholesterol, and potentially, cholesterol subgroup analyses may produce null results. Nonetheless, studies have consistently shown hypercholesterolemia in NHPI (Chiem et al., 2006; Mau et al., 2009; Moy et al., 2010; Sundaram et al., 2005), and therefore, further research needs to be conducted on the association between high cholesterol and MCI in NHPI.
Research also suggests that prediabetes (independent of diabetes) has been associated with adverse cognitive test results and cognitive decline (Dybjer et al., 2018; Marseglia et al., 2019). A study utilizing brain magnetic resonance imaging markers, including total brain tissue, white matter, and gray matter, showed that prediabetes was cross-sectionally associated with a smaller total brain tissue volume (p < .01), particularly smaller white matter volume (Marseglia et al., 2019). Dybjer et al. (2018) examined the relationship between prediabetes and cognitive function utilizing two cognitive tests, the Mini Mental State Examination (MMSE), measuring global cognitive function, and A Quick Test of Cognitive Speed (AQT), measuring processing speed and executive functioning. The results showed that those with prediabetes had worse cognitive function results than those without prediabetes. Similarly, our findings in NHPI showed a strong relationship between prediabetes and MCI. The sustained and prolonged exposure to insulin in prediabetics subsequently results in insulin resistance, whereby increasing oxidative stress and brain insulin signaling impairment, which may also subsequently lead to a neurodegeneration cascade in late AD (Bitra et al., 2015); therefore, early preventive efforts during prediabetes and/or borderline diabetes may potentially reduce AD risks in the NHPI community.
Studies have shown an association between diabetes and cardiovascular disease/stroke with cognitive decline (Biessels, & Despa, 2018; Kalaria et al., 2016); however, we did not show a relationship between these variables, which may be predominantly due to the small sample reporting of these respective conditions. Other limitations include the generalizability of our findings as our sample was recruited from Southern California. Further, our cross-sectional design makes it difficult to draw causal conclusions. However, via the utilization of a validated cognitive tool, as well as the CBPR approach, we were able to demonstrate important links between comorbid conditions and MCI. Additionally, due to cultural and linguistic hurdles, as well as historical suspicion/mistrust of research, recruiting participants from the NHPI populations can be difficult; therefore, we showed that with strategic CBPR collaborations, successful recruitment is feasible to investigate cognitive decline in NHPI older adults.
Research priorities for aging adults are becoming increasingly important as life expectancies increase and our population ages. Our findings demonstrate an association between high blood pressure, high cholesterol, and prediabetes with MCI in at-risk NHPI older adults. Research focusing on identifying risk factors for age-related disease, establishing effective preventative and treatment strategies in curbing comorbid conditions (which are all modifiable risk factors), and improving health outcomes is crucial for promoting healthful aging and meeting health needs for the NHPI community. Additionally, NHPI populations are disproportionately affected by these health conditions and are largely underrepresented in health research. Our findings emphasize the importance of continuing to address NHPI health disparities, as well as the need for culturally sensitive and targeted interventions to improve NHPI health outcomes.
Footnotes
Acknowledgements
Research reported in this publication was supported by the National Institute On Aging of the National Institutes of Health under Award Number R25AG069711. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We also acknowledge Ua’alani Hopi, MPH, Charlene Kazner, Monica Avila, MPH and Irma Rodriguez Hernandez, MPH for their assistance in data collection. We also acknowledge the contribution and collaboration of Dr. Ka'imi Sinclair, PhD, for sharing of study questionnaires and other protocols.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Institute on Aging of the National Institutes of Health (grant number R25AG069711).
