Long-term exposure to fine particulate matter (PM2.5) significantly raises diabetes risk, sounding the alarm on India's escalating health crisis
In a groundbreaking study conducted in India, researchers have uncovered compelling evidence linking air pollution to a surge in diabetes cases nationwide. This pioneering research demonstrates that extended exposure to fine particulate matter, known as PM2.5, is strongly associated with elevated blood sugar levels and an increased likelihood of developing type 2 diabetes mellitus (T2DM).
The study, which delved into data from over 12,000 adults participating in the Centre for Cardiometabolic Risk Reduction in South Asia (CARRS) cohort study based in Chennai and Delhi, shines a spotlight on a pressing concern amid the growing number of diabetes patients in India. The nation, with an estimated 77 million adults living with diabetes as of 2019, faces a potential crisis propelled by air pollution.
While diabetes is a multifaceted metabolic disorder influenced by various factors, this research underscores the pivotal role that air pollution may play, particularly in urban environments.
From 2010 to 2017, researchers monitored study participants' exposure to PM2.5 for seven years using high-resolution satellite-based models. Simultaneously, they tracked blood sugar levels and the incidence of T2DM within this cohort.
The findings reveal a disturbing correlation between residing in areas with higher PM2.5 levels and elevated fasting plasma glucose (FPG) and glycated haemoglobin (HbA1c) levels. HbA1c, a critical indicator of long-term blood sugar management, showed consistent changes.
More alarmingly, the study highlights that prolonged exposure to PM2.5 significantly escalates the risk of developing T2DM over the next seven years. This risk remained evident even after adjusting for diverse risk factors such as diet, physical activity, and smoking.
The results indicate that a mere 10 μg/m3 increase in annual PM2.5 exposure correlated with a 0.4 mg/dL rise in FPG levels, a 0.02% increase in HbA1c, and a staggering 23% higher risk of diabetes development. Crucially, this risk appeared to intensify in areas with lower PM2.5 concentrations, raising concerns that even relatively clean air may not be free from diabetes-related hazards.
Conducted by researchers from the Madras Diabetes Research Foundation in Chennai, the Public Health Foundation of India in Gurugram, and several American institutions, including the University of California, San Francisco, and the University of Washington, Seattle, the study marks a significant milestone as the first in India to establish a quantitative link between PM2.5 and diabetes risk within a highly polluted environment.
With annual average PM2.5 levels consistently exceeding WHO guidelines multiple times in Indian cities, these findings underscore the urgent imperative to combat air pollution and curtail the escalating diabetes burden.
This study aligns with previous research from Europe and North America, which also pointed to the relationship between air pollution and diabetes risk. A 2010 meta-analysis revealed that a 10 μg/m3 increase in PM2.5 exposure worldwide was linked to a 1% increase in diabetes prevalence. Subsequent studies in China and Taiwan further corroborated this potential connection.
The proposed mechanisms underlying this link include inflammation, oxidative stress, lipid accumulation in tissues, endothelial dysfunction, and autonomic imbalance. These effects, all triggered by air pollutants entering the body, can disrupt glucose and insulin regulation, contributing to diabetes.
However, earlier evidence primarily stemmed from developed countries with lower pollution levels, in contrast to the present study, which firmly establishes this risk within the context of Indian cities grappling with soaring PM2.5 levels.
The study leveraged data from the CARRS cohort study, a comprehensive population-based initiative spanning Chennai and Delhi. Over 12,600 participants aged 20 years or older were randomly recruited between 2010 and 2012 and followed up until 2017.
To estimate daily PM2.5 levels in the two cities, researchers employed satellite observations, meteorological data, land use patterns, and emission inventories. These exposure levels were intricately linked to the residential locations of the CARRS participants.
Baseline blood samples were collected, and subsequent follow-ups enabled the measurement of fasting blood glucose and HbA1c levels. Diabetes status was determined using established thresholds. The researchers meticulously analysed the associations between PM2.5 exposure over various periods, fluctuations in blood sugar parameters, and diabetes incidence.
In Delhi, a 10 μg/m3 increase in the 1-month average and 6-month average PM2.5 levels corresponded to 0.4 mg/dL and 0.7 mg/dL increases in blood glucose, respectively. In Chennai, the corresponding figures stood at 0.5 mg/dL and 0.6 mg/dL.
Notably, PM2.5 increases also resulted in slight but statistically significant elevations in HbA1c levels in both cities. When the data from both cities were pooled together, the effects remained remarkably consistent despite differing pollution levels.
Concerning diabetes incidence, the risk peaked at 1–1.5 years of exposure. In Delhi, the hazard ratio (HR) reached its zenith at 1.24 for a 10 μg/m3 annual PM2.5 increase over 1.5 years. The pooled estimate across both cities revealed an HR of 1.23, firmly establishing the link between long-term pollution exposure and diabetes risk.
Importantly, these results held independently of other risk factors such as diet, smoking, exercise, and alcohol use, all of which were meticulously adjusted for during the analysis.
Curiously, the exposure-response relationship displayed a non-linear pattern, with risk plateauing at exceptionally high exposures in Delhi. The researchers surmised that the incremental risk beyond a certain point was relatively minor.
The findings from this study serve as a stark reminder of the escalating air pollution levels in Indian cities and the many health risks they bring, extending beyond respiratory ailments.
While individual-level interventions such as dietary improvements and increased physical activity are undoubtedly crucial, this study underscores the paramount need for comprehensive policy measures addressing air pollution to foster an environment conducive to public health.
Encouragingly, the research highlights that diabetes risk diminishes with lower PM2.5 exposures, underscoring the significance of robust pollution control measures.
As India revises its National Clean Air Programme, experts assert urgent action is necessary to reduce PM2.5 levels, especially in metropolitan areas. This necessitates concerted efforts spanning various sectors, including transport, industry, waste management, energy, construction, and agriculture.
In addition to national-level initiatives, localised strategies tailored to address pollution hotspots and spikes within cities are imperative. The involvement of municipal bodies is pivotal in driving actionable change.