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A common class of insecticides puts farmers at high risk of diabetes (downtoearth,)

IN 2011, a 15-year-old girl from Madurai was admitted to hospital for diabetes ketoacidosis. It is a life-threatening condition that develops when cells in the body are unable to get the sugar (glucose) they need due to the lack of insulin. Krishnan Swaminathan, an endocrinologist and president of the Coimbatore-based Kovai Medical Centre and Hospital, saw that the girl was not responding to treatment. “We reinvestigated the case and found high residues of an organophosphate (OP) insecticide in her blood and urine samples. When we asked her parents, they told us she had consumed the insecticide because she had scored less marks in her school examination,” he says. Derived from phosphoric acid, OPs are a popular class of pesticides. They are also notorious as the poison chosen by farmers to commit suicide.

Around the time, the case of a 12-year-old boy suffering from a similar condition was reported from Mysuru, Karnataka. The boy had eaten tomatoes from a field without washing them only a few hours earlier. Swaminathan says that it was due to this impact of the chemical on the body’s insulin function that he first thought there could be a link between OP exposure and diabetes. The observations in these cases formed the premise of a study conducted by a team from the Madurai Kamaraj University to investigate the high prevalence of diabetes being reported from rural areas. “Chronic exposure to organophosphate not only induces diabetes but also leads to impaired glucose tolerance (type II diabetes) in both humans and mice,” says Ganesan Velmurugan, lead author of the paper published in the January issue of Genome Biology. Previous studies had shown a high prevalence of diabetes in rural Tamil Nadu, but this is the first study to link pesticide exposure to the disease.

The researchers surveyed 3,080 people from seven villages in Thirupparan-kundram block of Madurai district. Participants were above the age of 35 years. Almost 55 per cent of them were from the farming community and were, hence, more likely to be exposed to OPs. Based on the blood test results, it was found that the prevalence of diabetes among the farming community was three times higher (18.3 per cent) than that in the non-farming community (6.2 per cent), despite the low level of typical risk factors such as obesity, high cholesterol and physical inactivity.

Take the case of Sakthivel, a 50-year-old farmer from Vadapalanji village near Madurai. He grows vegetables such as tomatoes, okra, snake gourd and bitter gourd, in addition to paddy, on his 0.8-hectare farm. Once every week, he sprays his own farm and those of others with pesticides. He dislikes wearing a mask or gloves and even skips wearing protective boots. Until his blood was tested by the researchers in 2016, he was unaware that he was suffering from type II diabetes. Sakthivel is neither obese nor does he have a family history of the disease. Like others diagnosed with diabetes during the survey, he has now been put on metformin, a common diabetes medicine, and a strict diet.

Gut clues

To confirm whether chronic exposure to OPs leads to diabetes, the researchers fed insecticide-laced water to a group of mice for 180 days, which is equivalent to 12-15 years of human life. They found that the mice showed a slow and steady increase in their blood glucose levels, resulting in significantly high levels after 180 days.

Subramanya from Madurai uses monocrotophos pesticide
as suggested by agricultural colleges. It is banned for use
on vegetables (Photo: Megha Prakash)
Subramanya from Madurai uses monocrotophos pesticide as suggested by agricultural colleges. It is banned for use on vegetables (Photo: Megha Prakash)
Just like nerve agents used in chemical warfare, OPs inhibit the function of an enzyme called cholinesterase, which ensures proper functioning of the nervous system. But researchers were surprised to find no changes in levels of the enzyme in the treated mice. They then investigated whether gut microbiota may have a role to play in the developing of diabetes. They transplanted faecal material from OP-fed animals to a new set of mice and found that the latter exhibited significant glucose intolerance and developed diabetes. The authors also noticed changes in the gut microbiota, including higher numbers of OP-degrading bacterial enzymes. Degradation of organophosphates produces short-chain fatty acids—specifically acetate—which in turn lead to the generation of glucose, elevated blood sugar levels and glucose intolerance.

The findings of the study assume importance as India is the diabetes capital of the world. As of 2015, more than 69 million people in the country were estimated to be living with diabetes (see ‘Diabetes Capital’). Changing diets, sedentary lifestyle, and a genetic predisposition to developing the disease are expected to result in an increase in the number of type II diabetics to 79.4 million by 2030. With factors such as the increasing and indiscriminate use of pesticides now coming into play, diabetes no longer remains an urban preserve. 


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