Type 2 diabetes is a global public health concern. The consequences – loss of limbs, blindness, long term dependence on insulin injections – can greatly damage quality of life, and the financial impact on healthcare services can be large.
Meanwhile, despite global and national initiatives to reduce air pollution, exposure is a constant in day to day life, particularly in highly urbanized areas. There has been some investigation into the links between fine particles and increased risk of cardiovascular disease, but could ultrafine particles, those less than 100nm in size, pose a threat to the cardiovascular health in diabetes patients?
Two papers, published this week in Particle and Fibre Toxicology, one from authors based in China and another from a team working in Germany, suggest this might be the case. Both teams used electrocardiograms to assess heart function after patients with diabetes, or impaired glucose tolerance (pre diabetes), had been exposed to air pollutants for different lengths of time. Findings from both papers show that this exposure is linked to an increase in the risk of cardiovascular disease in these groups. Below, the authors explain the motives and methods behind their research.
Type 2 diabetes affects 114 million Chinese people and is the leading cause of blindness, lower extremity amputations, and hypertension, as well as a major cause of end-stage renal disease and cardiovascular disease.
A recent World Health Organization publication reported that fine particulate matter (PM2.5) represents the 4th leading cause of disability-adjusted life years in Asia. PM2.5 exposure contributes to insulin resistance and high blood pressure, but its role in perturbing glucose and blood pressure control in real world clinical settings has not been investigated.
Because of the increasing prevalence of diabetes worldwide and in China, and its association with an increasing risk of cardiovascular disease, we aimed to determine whether diabetes or impaired glucose tolerance may modify cardiovascular outcomes in those exposed to ambient particulates.
In our study, we followed a group of pre-diabetic and diabetic subjects under a chronic disease surveillance system managed by local center for disease control and surveillance in Shanghai. We found that with increasing concentration of ambient particles, there was a significant effect on heart function.
The greatest difference was seen in response to the smallest size fractions of particles (less than 100 nm), and a lesser difference was seen with particles of a diameter between 100-200 nm. Increased exposure to traffic-related pollutants BC, NO2 and CO, and combustion pollutant SO2, were also significantly associated with electrocardiogram parameter reductions.
Diabetes and gender appear to have a significant effect on the autonomic dysfunction associated with acute exposure to ultrafine particles and traffic pollution. Our results support the hypothesis that diabetes or impaired glucose tolerance may contribute to irregular functioning of the heart in response to traffic pollution exposure.
This highlights the need to control air pollution as a public health priority in China and to call for urgent attention to air pollution attributed chronic disease risk in countries currently under rapid industrialization and economic development
In our study, we were able to show that elevated ambient particle number concentrations are associated with immediate changes in the heart beats of individuals with type 2 diabetes or pre-diabetes. The association was independent of other factors such as weather or physical activity.
The observed associations with exposures were attributable to particles from outdoors as well as indoors, such as exposure to tobacco smoke. We decided to measure the total number of particles using a concentration particle counter. Based on extensive measurements, we knew that the total number count is dominated by particles below 100 nm, called ultrafine particles. Meanwhile, we used electrocardiogram readings to assess cardiac function, as they can measure changes continuously.
Individuals with diabetes have been identified as being especially susceptible to cardiovascular disease on days with high air pollution exposures. However, to control for the effect of medication which might mitigate the impact of ambient air pollution, we included a group of healthy individuals with early signs of impaired glucose metabolism. We were unable to see significant differences between the two subgroups studied.
Overall, the study demonstrated that personal activities result in exposure to combustion related particles in addition to fine particulate matter. These results were observed in a relatively clean air setting (below the current European standards for fine particles).
The results indicate that exposure to particles during times spent in traffic may impair cardiac function and thereby contribute to an elevated risk of triggering a heart attack. This suggests there is a need for further measures to protect the public from short-term exposure to ultrafine particles in urban environments, in addition to the currently regulated fine particles.
While regulation of fine particulate matter has been introduced, the risk of ultrafine particles is less well known. The immediacy of the risk of air pollution to those with type 2 diabetes, is exemplified by these two studies which, although conducted in very different countries, have resulted in a similar call for public health intervention.