Diabetes linked prospectively to pesticide use

Farmers and Others Using Pesticides Show Higher Diabetes Risk
By Michael Smith, North American Correspondent, MedPage Today
Published: June 05, 2008

http://www.medpagetoday.com/Endocrinology/Diabetes/tb/9715

Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine.

Long-term exposure to a range of insecticides and herbicides is associated with an increased risk of diabetes, epidemiologists here said.

In one example, the risk of diabetes was increased 94% for those who had used the insecticide heptachlor more than 100 days in a lifetime, compared with nonusers, according to Dale Sandler, Ph.D., of the National Institute of Environmental Health Sciences, and colleagues.

The finding emerged from the Agricultural Health Study, a prospective longitudinal look at 52,393 farmers and others who used insecticides and herbicides in the work in Iowa and North Carolina, Dr. Sandler and colleagues reported in the May issue of the American Journal of Epidemiology.

"The results suggest that pesticides may be a contributing factor for diabetes along with known risk factors such as obesity, lack of exercise and having a family history of diabetes," Dr. Sandler said in a statement.

The general public "is not entirely unexposed to these chemicals," added co-author Freya Kamel, Ph.D., also of the federal agency.

But she said levels of exposure are low and the traditional risk factors for diabetes -- overweight and lack of exercise -- remain the key elements in preventing the disease.

"I don't think anyone should panic," she said.

The volunteers in the current study were recruited in 1993 and completed a baseline survey on lifetime pesticide application practices and exposures and a brief medical history. Also, 44% of the volunteers completed a more detailed take-home questionnaire.

>From 1999 through 2003, participants were reached again for a follow-up telephone interview, and 33,457 (or 64%) gave updated information on their medical conditions, including diabetes.

After excluding those who had diabetes at baseline and those with missing information, Dr. Sandler and colleagues analyzed the effects of 50 chemicals on a total of 31,787 licensed applicators.

The study is "one of the largest studies looking at the potential effects of pesticides on diabetes incidence in adults," Dr. Kamel said. "It clearly shows that cumulative lifetime exposure is important and not just recent exposure," she added.

Of 50 chemicals evaluated, the study pinpointed five insecticides -- aldrin, chlordane, heptachlor, dichlorvos, and trichlorfon -- as well as the herbicides alachlor and cyanazine.

For all seven, the odds of developing diabetes increased with both any use and cumulative use, the researchers said.

For example, any use of heptachlor was associated with an odds ratio for diabetes of 1.20, with a 95% confidence interval from 1.01 to 1.43. Cumulative use of more than 100 days was associated with an odds ratio of 1.94, with a 95% confidence interval from 1.02 to 3.69.

Among the herbicides, any use of cyanazine was associated with an odds ratio for diabetes of 1.27, with a 95% confidence interval from 1.09 to 1.47, while cumulative use of more than 100 days was associated with an odds ratio of 1.38, with a 95% confidence interval from 1.10 to 1.72.

All seven of the compounds associated with diabetes were chlorinated, although only about half of the evaluated chemicals were chlorinated, the researchers found.

"The fact that all seven of these pesticides are chlorinated provides us with an important clue for further research," Dr. Kamel said. "It's the only thing we can see that they have in common and it's not clear what that would mean."

"The next step is really for the toxicologists," she said.

The authors pointed out several limitations of the study including the use of self-reported diagnosis of diabetes and an inability to control for exercise and diet.

They also noted that "there was a strong relation between diabetes incidence and state of residence; applicators from North Carolina had a two-fold increased odds of diabetes compared with applicators in Iowa, even after adjustment for age, body mass index, and smoking. This may reflect differences in health and lifestyle status between the states that were not completely controlled for by age, body mass index, and smoking alone."

The study was supported by the NIEHS. The researchers did not declare any competing interests.

Primary source: American Journal of Epidemiology
Source reference:
Montgomery MP, et al "Incident diabetes and pesticide exposure among
licensed pesticide applicators: Agricultural health study, 1993-2003"
Am J Epidemiol 2008; 167: 1235-1246.

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http://aje.oxfordjournals.org/cgi/content/abstract/167/10/1235?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=1&author1=Montgomery&andorexacttitle=and&andorexacttitleabs=and&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT%22
or
http://tinyurl.com/6zu8cq

ORIGINAL CONTRIBUTIONS
Incident Diabetes and Pesticide Exposure among Licensed Pesticide
Applicators: Agricultural Health Study, 1993–2003
M. P. Montgomery1, F. Kamel1, T. M. Saldana2, M. C. R. Alavanja3 and
D. P. Sandler1

1 Epidemiology Branch, National Institute of Environmental Health
Sciences, National Institutes of Health, Department of Health and
Human Services, Research Triangle Park, NC
2 Social & Scientific Systems, Durham, NC
3 Occupational and Environmental Epidemiology Branch, National Cancer
Institute, Bethesda, MD

Correspondence to Dr. Dale P. Sandler, Epidemiology Branch, National
Institute of Environmental Health Sciences, P.O. Box 12233, 111 T. W.
Alexander Drive, Research Triangle Park, NC 27709 (e-mail:
sandler@niehs.nih.gov).

Received for publication October 2, 2007. Accepted for publication
January 25, 2008.

Exposure to certain environmental toxicants may be associated with
increased risk of developing diabetes. The authors' aim was to
investigate the relation between lifetime exposure to specific
agricultural pesticides and diabetes incidence among pesticide
applicators. The study included 33,457 licensed applicators,
predominantly non-Hispanic White males, enrolled in the Agricultural
Health Study. Incident diabetes was self-reported in a 5-year
follow-up interview (1999–2003), giving 1,176 diabetics and 30,611
nondiabetics for analysis. Lifetime exposure to pesticides and
covariate information were reported by participants at enrollment
(1993–1997). Using logistic regression, the authors considered two
primary measures of pesticide exposure: ever use and cumulative
lifetime days of use. They found seven specific pesticides (aldrin,
chlordane, heptachlor, dichlorvos, trichlorfon, alachlor, and
cyanazine) for which the odds of diabetes incidence increased with
both ever use and cumulative days of use. Applicators who had used the
organochlorine insecticides aldrin, chlordane, and heptachlor more
than 100 lifetime days had 51%, 63%, and 94% increased odds of
diabetes, respectively. The observed association of organochlorine and
organophosphate insecticides with diabetes is consistent with results
from previous human and animal studies. Long-term exposure from
handling certain pesticides, in particular, organochlorine and
organophosphate insecticides, may be associated with increased risk of
diabetes.