New Delhi: Long-term exposure to fine Particulate Matter (PM2.5) is associated with a 10 to 16 per cent higher risk of developing Type 2 diabetes for every 10 microgram per cubic metre increase in exposure, according to a global review of research published in the Journal of Vascular Diseases.
The findings, published ahead of World Diabetes Day on November 14, are based on an umbrella review of 13 systematic reviews and meta-analyses, covering more than 200 million cumulative participant observations from studies across different parts of the world.
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The review, titled 'Association Between PM2.5 Exposure and Type 2 Diabetes Across the Cardiovascular-Kidney-Metabolic (CKM) Continuum (APEX-T2D)', has been co-authored by Dr Anoop Misra, Executive Chairman and Director, Diabetes and Endocrinology, Fortis C-DOC Hospital, New Delhi.
The researchers found that six of the seven reviews examining new cases of Type 2 diabetes reported an increased risk ranging between 10 and 16 per cent for every 10 microgram per cubic metre rise in long-term PM2.5 exposure.
The association was observed across Asian and Western populations, with the findings also indicating a dose-response relationship, wherein the risk increased with higher levels of exposure.
What is PM2.5?
PM2.5 refers to fine particulate matter with a diameter of less than 2.5 micrometres, which can penetrate deep into the lungs and trigger responses beyond the respiratory system.
The researchers said possible biological pathways linking air pollution to diabetes include systemic inflammation, oxidative stress, endothelial dysfunction and impaired insulin signalling. However, these mechanisms remain incompletely understood.
The review also found positive associations between PM2.5 exposure and the prevalence of Type 2 diabetes, diabetes-related mortality and fasting blood glucose levels. However, the evidence for these secondary outcomes was rated very low.
The researchers cautioned that the findings establish an association rather than a direct cause-and-effect relationship. The evidence for the increased incidence of Type 2 diabetes was rated as being of low certainty, given the observational nature of the studies and substantial variations in their findings.
They also noted that the more than 200 million figure represents cumulative participant observations across the reviews and not 200 million unique individuals, as several reviews included overlapping studies and populations.
The association was also reported in populations with annual average PM2.5 exposure levels around 5 to 7 micrograms per cubic metre, close to the World Health Organisation's annual guideline of 5 micrograms per cubic metre. However, the review did not establish a safe threshold for exposure.
Highlighting the public health implications, the researchers said air pollution should be considered as part of cardiometabolic disease prevention strategies, particularly in South Asia, where high pollution levels coincide with a growing burden of metabolic disorders.
They called for greater air-quality monitoring, the inclusion of air pollution in diabetes prevention and research frameworks, and more long-term studies to establish whether reducing exposure can lower the incidence of diabetes.
The researchers, however, said existing evidence does not establish that a specific reduction in PM2.5 exposure would lead to a proportional decline in diabetes cases.
Type 2 diabetes, which affects more than 500 million adults globally, is commonly associated with factors such as obesity, physical inactivity, dietary habits and genetic susceptibility. The review adds long-term environmental exposure to the growing body of research examining factors associated with the disease.
