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The Chinese University of Hong Kong (CUHK)’s Faculty of Medicine (CU Medicine) and The University of Hong Kong (HKU)’s Faculty of Architecture, along with collaborators and scholars, conducted the first longitudinal investigation into the life-course associations between ambient fine particulate matter (PM_2.5) and the prevalence of prediabetes and diabetes. The results revealed a clear association at every life stage, particularly in adulthood. Given the rising risks and burden of diabetes-related health issues, there is an urgent need for effective life-course air pollution control. Detailed results have been published in the prestigious international medical journal Diabetes Care.

The rising challenge of prediabetes: a global health concern

Prediabetes is a medical condition marked by elevated blood glucose levels that do not yet qualify as diabetes. The International Diabetes Federation indicated that in 2021, between 319 million and 541 million adults globally were living with prediabetes, a figure projected to rise to as many as 730 million by 2045. This increase poses a significant burden to society, as a systematic review reveals that 26% to 50% of individuals with prediabetes progress to diabetes within five years of diagnosis.

The implications of prediabetes extend beyond the potential for diabetes itself. Individuals with this condition face heightened risks of premature mortality and various complications, including cardiovascular disease, chronic kidney disease and certain cancers. Risk factors for diabetes often emerge during the prediabetic phase and can be categorised into non-modifiable factors like age and genetics, and modifiable factors such as obesity, lifestyle choices and environmental exposure. Of particular concern is the impact of ambient air pollution, specifically fine particulate matter (PM_2.5), which has been linked to insulin resistance and diabetes risk.

Chronic PM_2.5 exposure associated with higher risks of prediabetes and diabetes

The researchers found that chronic exposure to ambient PM_2.5  during different life stages was linked to higher prevalence and incidence rates of prediabetes and diabetes, as well as elevated fasting plasma glucose (FPG) levels in adulthood[1]. The impact of these associations had not been previously well understood. This research represented the first longitudinal investigation into life-course associations between PM_2.5 exposure and the prevalence of prediabetes and diabetes, tracking participants from school age (6 to 14 years old), adolescence (15 to 19 years old) to adulthood (20 years old and above).

The study included 4,551 participants, comprising 2,449 males and 2,102 females, with a mean age of 15.91 years. Participants made a total of 19,593 medical visits, with 71% of participants making at least three medical visits. The average follow-up period was 9.93 years (standard deviation = 3.89 years). Most participants reported never smoking during adolescence (86%) and had no hypertension (97%) or dyslipidaemia (78%).

Identifying critical life stages to formulate air pollution control strategies

The study revealed that inhalation of PM_2.5 particles would result in systemic oxidative stress and inflammation, being the key contributors to insulin resistance. The researchers employed three life-course models to assess the impact of PM_2.5 exposure at different life stages, revealing that exposure during adulthood would increase the odds of having prediabetes or diabetes in adulthood by 29% compared with exposure during school age (15%) and adolescence stages (18%), respectively[2].

Professor Martin Wong Chi-sang, senior co-corresponding author of the study, from The Jockey Club School of Public Health and Primary Care at CU Medicine, said: “Our study emphasises the importance of reducing PM_2.5 exposure to mitigate the risks of prediabetes and diabetes. Future research should aim to extend follow-up periods to include critical developmental stages and explore the long-term impacts of PM_2.5 exposure.”

The study highlights the urgent need for life-course air pollution control strategies to effectively address and mitigate the rising burden of diabetes-related health issues. By identifying critical exposure periods, such strategies can help target interventions and improve public health outcomes.

Professor Guo Cui, co-corresponding author of the study and Assistant Professor from the Department of Urban Planning and Design, Faculty of Architecture of HKU, added: ‘‘Although we utilised a high-resolution spatial-temporal model to assess PM_2.5 exposure, improving the accuracy of our findings, some limitations must be acknowledged, such as the exclusion of additional air pollutants and the lack of prenatal exposure data.”

[1] The researchers’ findings corroborate existing literature, which indicates that:

• Each standard deviation increase in the three-year average PM₅ concentration correlates with an 8% increase in the odds of developing diabetes. This connection highlights the urgent need for effective air pollution control strategies to mitigate the growing burden of diabetes globally.
• The association between fasting plasma glucose (FPG) levels and age was nonlinear, with FPG

[2]  The researchers detailed the longitudinal associations between chronic PM_2.5 exposure and the presence of prediabetes or diabetes during the study. Each 10 µg/m³ increase in PM_2.5 was linked to a 32% (95% CI: 13%, 54%) increase in the odds of developing prediabetes or diabetes.