Mom's Exposure to Pesticide Raises Risk of Infant Leukemia

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A mother's exposure to pesticides during pregnancy may be linked to rare types of leukemias that are diagnosed in children younger than two, according to a study from Brazil. The children whose mothers were exposed at home or at work were two to seven times more likely to have one of the two cancers studied than those whose mothers reported no pesticide exposure. Infants younger than eleven months old were up to seven times more likely to have leukemia if their mothers used the insecticide permethrin. The results suggest that women of reproductive age should minimize their pesticide exposure before and during pregnancy and while nursing.

This study is important because it focused on children younger than two years old and included both work and home exposures. The short time needed for cancers to develop in the infants suggests pre-birth exposures are important for the leukemias studied, the authors noted.

The findings support previous studies that indicate maternal pesticide exposure may play a role in childhood leukemia. Prenatal pesticide exposure has been linked to leukemia in older children. Few of these studies have looked at infants and toddlers or considered household pesticide use during the prenatal period. Also, most of the studies focused on occupational exposures.

Pyrethroids — including permethrin — control insects by interfering with the nervous system. These synthetic versions of natural pyrethroids found in chrysanthemum flowers are regulated and used on a variety of crops, in some pet products to control fleas and ticks, on clothing, inside homes and buildings, and to kill mosquitoes. Pyrethroids may be slight carcinogens, but animal and human cancer studies have mixed results.

Infant leukemias are rare and usually diagnosed between birth and eighteen months. Risk factors for childhood leukemias include environmental agents like pesticides, which may alter DNA during development.

In this ongoing infant leukemia study from Brazil, researchers asked mothers about their pesticide exposure three months before pregnancy, while pregnant and three months after pregnancy when they were nursing. The women reported their home, work and agricultural contact with pesticides (at least once) between 1999 and 2007.

Pesticide exposures from mothers of 252 children younger than 2 years old and diagnosed with either acute lymphoid leukemia (ALL) or acute myeloid leukemia (AML) were compared to exposures from mothers of 423 children of the same age without cancer.

Researchers found that children from birth to eleven months old whose mothers were exposed to pesticides during pregnancy were two times more likely to be diagnosed with ALL and five times more likely to be diagnosed with AML, compared to children of mothers who did not report such use. Children 12 to 23 months old whose mothers reported pesticide use during pregnancy were almost twice as likely to be diagnosed with ALL compared to those who did not report such exposure.

Overall, mothers’ exposure to seven pyrethroids and "unspecified solvents" was associated with childhood leukemia. Specifically, children from birth to 11 months old whose mothers reported use of permethrin were about 2.5 and 7 times more likely to be diagnosed with AML and ALL, respectively, compared to children of mothers who reported not using this pesticide. The mothers’ pesticide exposure related to agricultural activities was also associated with diagnosis of ALL and AML.

Because this is a case control study, recall bias — or not accurately remembering details — may be a problem. Mothers of children with ALL or AML may be more likely to recall pesticide use compared to mothers of children without any cancers.

According to the authors, future studies should explore the genetic and molecular mechanisms that determine susceptibility to pesticide exposures and the development of childhood leukemia.

This report was originally published by EnvironmentalHealthNews.org

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