Air pollution amplifies dementia risk in cardiometabolic disease patients

New research reveals how simple lifestyle changes can mitigate the dual threat of cardiometabolic diseases and air pollution on cognitive health.

Study: Association between air pollution and lifestyle with the risk of developing mild cognitive impairment and dementia in individuals with cardiometabolic diseases. Image Credit: NDAB Creativity / Shutterstock

In a recent study published in the journal Scientific Reports, researchers investigated the risk of mild cognitive impairment (MCI) and dementia in cardiometabolic disease (CMD) patients. They found that, compared to healthy ‘normal’ individuals, CMD patients were at significantly higher MCI and dementia risk.

Patients with three CMDs had the highest risk, with hazard ratios (HR) of 1.951 for MCI, 1.554 for all-cause dementia, 1.216 for Alzheimer’s disease, and 2.032 for vascular dementia. Higher simultaneous CMD counts were associated with a greater likelihood of MCI and dementia.

Ambient air pollution exacerbated these outcomes, with pollutants such as PM2.5, NO2, and NOX being particularly impactful. However, a healthy lifestyle decreased the strength of these associations.

Together, the present study suggests that maintaining a healthy lifestyle is critical to preventing MCI and dementia onset. Since both of these conditions are lifelong and remain without a cure, these findings can help provide clinicians, healthcare providers, and CMD patients with the information required to counter the rising prevalence of these debilitating diseases.

Background

‘Dementia’ is the umbrella term for identifying diseases affecting individuals’ memory, language, and other thinking abilities essential to daily activities. It is a severely debilitating condition known to alter patients’ personalities, moods, and behaviors. Unfortunately, hitherto, no cure for dementia has been discovered, making prevention the priority of current research against the condition.

Alarmingly, global dementia prevalence is rising at unprecedented rates, up by 117% in a little over two decades (1990–2016). Current estimates reveal that more than 57 million individuals live with dementia, with projected economic losses exceeding $1,313 billion.

Research hypothesizes that while genetics play a significant role in dementia prevalence, the globally aging population, suboptimal lifestyle choices, and increased pollution levels may exacerbate dementia risk.

Clinical studies have established the association between cardiometabolic diseases (CMDs; e.g., type 2 diabetes mellitus [T2DM], coronary heart disease [CHD], and stroke) and dementia, with the former almost doubling the latter’s onset risk. Similar associations between CMDs and mild cognitive impairments (MCIs) have been independently documented.

Notably, individuals with two or three CMD diagnoses were found to have significantly higher risks, with HRs for vascular dementia rising to 6.632 in those with all three CMDs. However, the cumulative impacts of multiple CMDs, ambient pollution levels, and lifestyles remain unknown.

About the Study

The present study aimed to unravel the concurrent impacts of ambient air pollution and lifestyle scores on dementia/MCI risk in CMD patients. Study data was obtained from the United Kingdom (UK) Biobank, an extensive biomedical database comprising more than 500,000 UK-based adults (ages 39–74 years). Of the 502,370 participants screened for the study, 63,689 presented incomplete sociodemographic, lifestyle, and medical information and were excluded from subsequent analyses.

UK Biobank medical history data was used to assess the number and severity of CMDs within the study cohort. The same datasets also included MCI and dementia diagnoses, with follow-up periods of ~15.12 years. Exposure to air pollutants, such as PM2.5, PM10, and NO2, was estimated using land use regression (LUR) modeling.

Structured baseline questionnaires were used to evaluate participants’ healthy lifestyle scores. These questionnaires comprised seven items, including 1. diet, 2. alcohol consumption, 3. smoking status, 4. physical activity levels, 5. sedentary behaviors, 6. social relationships, and 7. sleep patterns.

Statistical analyses included latent class analysis (LCA) for the identification of ambient air pollutant patterns, Cox proportional regression models for dementia/MCI risk assessments, and sensitivity analyses.

Study Findings

Of the 438,681 participants included in the analyses, 17.11% (n = 75,056) were diagnosed with CMDs. Of these, 15.12% had suffered from one CMD, 1.90% suffered from two simultaneous CMDs, and 0.09% suffered from three CMDs. Statistical analyses revealed that ambient air pollution and poor lifestyles independently contributed to dementia/MCI prevalence, with dementia/MCI patients generally exhibiting poorer lifestyle choices and higher air pollution exposures than their ‘normal’ counterparts.

“The risk of developing mild cognitive impairment, all-cause dementia, Alzheimer’s disease, and vascular dementia in patients with CMDs was 1.951, 1.554, 1.216, and 2.032 times higher than in those without CMDs, respectively.”

CMD was found to significantly increase dementia and MCI risk by between 121 and 203%. The number of concurrent CMDs was found to exacerbate these outcomes – patients with two or three CMD diagnoses were substantially more likely to develop MCI or dementia than those with only one CMD.

When analyzed together, air pollutants such as PM2.5 and NO2 consistently increased dementia and MCI risk. Lifestyle behaviors (easily modifiable) attenuated air pollution’s impacts, suggesting a protective effect of these behaviors on future dementia/MCI incidence.

Conclusions

The present study is the first to evaluate the associations between CMD (presence and number of concurrent diagnoses) with MCI and dementia risk while simultaneously investigating the impacts of ambient air pollution and lifestyle choices on MCI/dementia outcomes. It highlights the cumulatively escalating risk of dementia/MCI in CMD patients, directly scaling with the number of concurrent CMD diagnoses.

Patients exposed to high pollution levels but following healthier lifestyle behaviors demonstrated lower risks, emphasizing the modifiable nature of lifestyle factors.

Notably, while both ambient air quality and lifestyle scores were found to impact MCI/dementia risk outcomes, the latter is easily modifiable and can be leveraged to protect against MCI/dementia onset.