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Agricultural Health Study

Key Points

• The Agricultural Health Study (AHS) is designed to investigate relationships between 

aspects of living and working on a farm―including hazardous substance 

exposures―and cancer risk, as well as relationships with other health problems (see 

Question 1).

• The AHS cohort includes nearly 90,000 men and women who live in Iowa or North 

Carolina (see Question 2).

• Most of the cancer research in the AHS has focused on pesticides (see Question 5).

• Thus far, researchers have investigated more than 20 pesticides. Some of these 

analyses have suggested that people exposed to certain pesticides may have an 

increased risk of developing one or more types of cancer (see Question 5).

1. What is the Agricultural Health Study?

In 1993, scientists from the National Cancer Institute, the National Institute of Environmental Health 

Sciences, and the Environmental Protection Agency (EPA) began a research project known as the 

Agricultural Health Study (AHS) to evaluate the role of agricultural exposures in the development of 

cancer and other diseases in members of the farming community. The National Institute for 

Occupational Safety and Health joined the study in 2000.

The AHS is also providing an opportunity to assess the effects of diet, cooking methods, and other 

lifestyle and genetic factors on the risks of cancer and other diseases. The results will provide 

information that can be used to create a safe work environment and a healthy lifestyle for agricultural 

workers and their families.

More information about the study can be found online at http://www.aghealth.nci.nih.gov/.

2. Who are the participants?

The vast majority of the nearly 90,000 participants in the AHS are either farmers or the wives of 

farmers; about 52,000 are farmers and 32,000 are wives of farmers. All of the participants were

recruited in North Carolina or Iowa.

Participants classified as "private pesticide applicators" are farmers or nursery workers. The study also 

includes a small percentage of "commercial pesticide applicators" from Iowa who work for pest control 

companies or for businesses, such as warehouses or grain mills, that use pesticides regularly; about 

5,000 participants are commercial applicators. 

3. What are some of the cancer trends among farmers?

Farmers in many countries, including the United States, have lower overall death rates and cancer 

rates than the general population. Lower death rates among farmers for heart disease and cancers of 

the lung, esophagus, bladder, and colon, in particular, are thought to be due, at least in part, to lower 

smoking rates, as well as more physically active lifestyles and dietary factors.

However, compared with the general population, the rates for certain diseases, including some types 

of cancer, appear to be higher among agricultural workers, which may be related to exposures that 
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are common in their work environments. For example, farming communities have higher rates of leukemia, 

non-Hodgkin lymphoma, multiple myeloma, and soft tissue sarcoma, as well as cancers of the skin, lip, 

stomach, brain, and prostate.

Even though no one set of risk factors explains these higher cancer rates, the range of environmental 

exposures in the farming community is of concern. Farmers, farm workers, and farm family members may be 

exposed to substances such as pesticides, engine exhausts, solvents, dusts, animal viruses, fertilizers, fuels, 

and specific microbes that may account for these elevated cancer rates. However, human studies reported to 

date have not allowed researchers to sort out which of these factors may be linked to which cancer types.

4. What types of information do AHS participants provide during the study?

From 1993 through 1997, when participants were being recruited for the study, they completed a 

questionnaire about their crops and livestock, the pesticides and personal protective equipment they used, 

how they applied pesticides, and other things they may have been exposed to on the farm, such as solvents, 

grain dusts, and welding fumes. They were also asked about nonfarm activities and exposures that may affect 

disease risks, such as diet, exercise, alcohol consumption, medical conditions, family history of cancer, other 

occupations, and smoking history. 

Since then, researchers have been using the following methods to collect additional information:

• Computer-assisted telephone interviews to gather information about pesticide use since study enrollment, 

changes in health status, and detailed information about farming and work practices. 

• Mailed dietary health questionnaires to gather detailed information about cooking practices and diet. 

• Collection of buccal (cheek) cells to determine whether specific alterations found in DNA are related to 

disease susceptibilities associated with agricultural exposures. 

• Records from cancer registries in each state to determine which participants developed cancer. 

• Records from the U.S. National Death Index, a computerized index of death records collected from all 

state vital statistics offices and available to scientists for medical and health research. 

In addition, a series of smaller analyses are focusing on risk factors for specific diseases. These analyses may 

involve additional questionnaires and the collection of blood, tumor, urine, or dust samples.

5. What have researchers learned so far about farmers and cancer risk?

Most of the cancer research in the AHS has focused on pesticides, which are chemicals used to kill invasive 

insects, weeds, or small animals. In some cases, relationships between these pesticides and human cancer 

were examined for the first time in the AHS. 

Thus far, researchers have evaluated more than 20 pesticides to determine whether the farmers who use 

them have increased risks of developing cancer. Some of these analyses have shown that people exposed to 

certain pesticides have an increased risk of developing certain cancers, but further research is needed to 

confirm these findings and to evaluate the potential mechanisms by which pesticides might influence cancer 

risk. 

For example, a study from the AHS reported in 2009 that people who use the weed killer imazethapyr have 

increased risks of bladder cancer and colon cancer. Imazethapyr is in a class of chemicals known as aromatic 

amines. It was first used in the United States in 1989, and, since then, has been one of the most commonly 

used herbicides for killing weeds in soybean, dry bean, alfalfa, and other crop fields. 

Studies in mice and rats led the EPA to classify imazethapyr as unlikely to be a human carcinogen. But, in the 

AHS, people with the highest cumulative lifetime exposure had more than twice the risk (137 percent increase 

in risk) of developing bladder cancer compared with those who had no exposure to the chemical. Similarly, the 

risk of colon cancer (mostly tumors in the proximal colon, where food enters during digestion) was nearly 

twice as high as normal (78 percent increased risk) among farmers who had the highest level of exposure 

compared with those who had no exposure to the chemical. 
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In addition, a condition called monoclonal gammopathy of undetermined significance (MGUS), which 

commonly precedes multiple myeloma, was found in blood samples of men in the AHS at twice the rate it was 

found in blood samples of men in Minnesota who were not part of the AHS cohort. This increased risk of MGUS 

was observed among men who used the chlorinated insecticide dieldrin, the fumigant mixture

carbon-tetrachloride/carbon disulfide, the fungicide chlorothalonil, and possibly other pesticides. Now, a larger 

study within the AHS is looking more closely at the risk of MGUS with use of specific pesticides.

In 2011, AHS researchers reported an analysis of farmers who use the weed killer atrazine, which is a type of 

chemical known as a triazine. In this analysis, farmers who used atrazine the most often had a similar overall 

cancer risk to those who used atrazine the least often, but those with the highest exposures had a slightly 

increased risk of thyroid cancer. However, the number of cancer cases was too few for the finding to be 

considered conclusive.

Atrazine causes mammary tumors in rats but is not classified as a carcinogen in humans. Atrazine is an 

endocrine disruptor—meaning that it interferes with normal hormone signals in the body—as demonstrated in 

amphibians, birds, and rodents that have been exposed to it at high concentrations.

More information about what researchers have learned about cancer, other health problems, and risk factors 

among farmers is available in the AHS publications list at http://www.aghealth.nci.nih.gov/publications.html.

Selected References

1. Koutros S, Alavanja MC, Lubin JH, et al. An update of cancer incidence in the Agricultural Health Study. 

Journal of Occupational and Environmental Medicine 2010; 52(11):1098–1105. [PubMed Abstract]

2. Koutros S, Lynch CF, Ma X, et al. Heterocyclic aromatic amine pesticide use and human cancer risk: results 

from the U.S. Agricultural Health Study. International Journal of Cancer 2009; 24(5):1206–1212. [PubMed 

Abstract]

3. Landgren O, Kyle RA, Hoppin JA, et al. Pesticide exposure and risk of monoclonal gammopathy of 

undetermined significance in the Agricultural Health Study. Blood 2009; 113(25):6386–6391. [PubMed 

Abstract]

4. Beane Freeman LE, Rusiecki JA, Hoppin JA, et al. Atrazine and cancer incidence among pesticide applicators in 

the Agricultural Health Study (1994–2007). Environmental Health Perspectives 2011; online May 27, 

doi:10.1289/ehp.1103561. [PubMed Abstract]

# # #

Related NCI materials and Web pages:

• Agricultural Health Study Home Page 

(http://www.aghealth.nci.nih.gov)

• Cancer Causes and Risk Factors Home Page 

(http://www.cancer.gov/cancertopics/causes)

• Understanding Cancer Series: Cancer and the Environment 

(http://www.cancer.gov/cancertopics/understandingcancer/environment)

How can we help?

We offer comprehensive research-based information for patients and their families, health professionals, cancer 

researchers, advocates, and the public.

• Call NCI’s Cancer Information Service at 1–800–4–CANCER (1–800–422–6237)

• Visit us at http://www.cancer.gov or http://www.cancer.gov/espanol

• Chat using LiveHelp, NCI’s instant messaging service, at http://www.cancer.gov/livehelp
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• E-mail us at cancergovstaff@mail.nih.gov

• Order publications at http://www.cancer.gov/publications or by calling 1–800–4–CANCER

• Get help with quitting smoking at 1–877–44U–QUIT (1–877–448–7848)

This fact sheet was reviewed on 6/16/11