Adverse Health Effect of Environmental Heavy Metals on Diabetes

ABSTRACT

Type 2 diabetes (T2D) and its complications constitute a major public health problem for both developed and developing countries due to the high rate of morbidity and mortality associated with the disease.  New evidence from both experimental and human studies has resulted in increased interest in analyzing the relationship between T2D and heavy metal exposures that are ubiquitous in the environment. Vellore district is a major leather- processing centre in Tamil Nadu, with an estimated 60,000 tannery workers. Tannery processing involves several chemical processes.

Due to large-scale production and consumption, heavy metals are thrown into the environment in large quantities through solid waste and wastewater disposal.  Tannery workers exposure to heavy metals occurs through inhalation of dust, direct ingestion of polluted soil and water. To determine the metal concentration in water and soil samples collected near tanneries using standard protocol.

We studied the incidence of diabetes and pre-diabetes among tannery industrial workers exposed to metals. Randomly selected 500 tannery workers (433-male and 67-female workers) of age between 25 to 60 years of age were included in the study. A standardized, structured questionnaire was used to collect epidemiological information.

Physical examinations and laboratory tests were conducted to evaluate the health status of the workers and to measure various biomarkers including blood sugar, lipids, and metal concentrations in blood and urine. In connection to plasma cations and intracellular markers and mediators, the results show that plasma from T2DM patients contain significantly (p<0.05) more  Na+, Mg2+ , Ca2+, Fe2+, Zn2+ and Cu2+ compared to plasma levels from age-match healthy controls. The biochemical parameters and inflammatory mediators which normally serve as independent predisposing risk factors for T2DM among workers compared to age-match healthy controls.

Similarly, We measured the concentrations of kidney and liver function markers such as urea, creatinine, alkaline phosphatase, ALT, AST, GGT, total protein and albumin increased significantly (p<0.05) compared to healthy controls. The same is also true for glucose, total cholesterol, triglycerides, CRP, HbA1c, WBC where the blood from T2DM patients contained elevated concentrations compared to blood from healthy age-matched control patients. The association between excessive weight gain, central adiposity and the development of T2DM is convincing. The relationship has been frequently demonstrated in longitudinal studies in diverse populations, with a striking gradient of risk apparent with increasing levels of BMI, adult weight gain, waist circumference and waist-to-hip ratio.

However, the mean concentrations of heavy metals were significantly higher in blood samples of diabetic patients as compared to control subjects, suggesting that toxic metals may play a role in the development of diabetes mellitus. We measured fasting plasma glucose (FPG) and impaired fasting glucose (IFG) among 500 workers ( 433 - male and 67 -female) of various tanneries in Vellore district in during the years 2013-2015 using standard protocol. Individuals with FPG ?126 mg/dl or on medications for diabetes were considered to have diabetes mellitus, FPG ?100 mg/dl and ?125/dl mg as pre-diabetic, and FPG 100 mg/dl as normal. We observed the hyperglycemia, increased levels of total cholesterol and low density cholesterol (LDL) and several other factors like race, origin, gender and smoking, lack of exercise, genetics as well as considerable variations in the levels of inflammatory markers including C-reactive protein (CRP), C-peptide and fatty acid binding protein (FABP) are all involved in the pathogenesis of insulin resistance.  Occupations associated with higher levels of heavy metal exposure were associated with an increased risk of diabetes in this cohort. The overall prevalence of diabetes and prediabetes was 7.5% and 16.8% respectively. More studies are needed to confirm this observed association.

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