"This is the first time researchers have conducted a systematic survey of a woman's diet and linked it to the risk of childhood leukemia," said Dr. Kenneth Olden, director of the National Institute of Environmental Health Sciences, the federal agency that funded the study. NIEHS is a component of the National Institutes of Health.

The study was conducted by researchers at the University of California, Berkeley, and the study results are published in the August 2004 issue of Cancer Causes and Control.

Researchers compared 138 women who each had a child diagnosed with acute lymphoblastic leukemia (ALL) with a control group of 138 women whose children did not have cancer. The children of all the women in the study were matched by sex, age, race, and county of residence at birth.

After comparing the women's diets in the 12 months prior to pregnancy, researchers found that the higher the intake of vegetables, fruit and foods in the protein group, the lower the risk of having a child with leukemia.

One of the more surprising results of the study is the emergence of protein sources, such as beef and beans, as a beneficial food group in lowering childhood leukemia risk. "The health benefits of fruits and vegetables have been known for a long time," said principal investigator Gladys Block, professor of epidemiology and public health nutrition at U.C. Berkeley. "What we found in this study is that the protein foods group is also very important."

The researchers looked further and found that glutathione was the nutrient in the protein group with a strong link to lower cancer risk. Glutathione is an antioxidant found in both meat and legumes, and it plays a role in the synthesis and repair of DNA, as well as the detoxification of certain harmful compounds.

Within the fruit and vegetable food groups, certain foods - including carrots, string beans and cantaloupe - stood out as having stronger links to lower childhood leukemia risk. The researchers point to the benefits of nutrients, such as carotenoids, in those foods as potential protective factors. National guidelines recommend that people eat at least five servings of fruits and vegetables every day, and two to three servings of foods from the protein group.

"Fetal exposure to nutritional factors has a lot to do with what mom eats," said Christopher Jensen, a nutritional epidemiologist at U.C. Berkeley and lead author of the paper. "These findings show how vital it is that women hoping to get pregnant, as well as expectant moms, understand that critical nutrients in vegetables, fruit and foods containing protein, such as meat, fish, beans and nuts, may protect the health of their unborn children."

The few studies that have been conducted on maternal diet and childhood cancer risk looked only at specific foods or supplements, and results have been mixed. This study is the first attempt to capture a woman's overall dietary pattern - using a 76-food-item questionnaire - and its relationship to the development of leukemia in a child. Researchers also studied the use of vitamin supplements, but did not find a statistically significant link to childhood leukemia risk.

A growing number of scientists believe that genetic changes linked to cancer later in life begin in the womb. "It goes back to the old saying to expectant mothers, 'You're eating for two,'" said co-author Patricia Buffler, U.C. Berkeley professor of epidemiology and head of the federally funded Northern California Childhood Leukemia Study. "We're starting to see the importance of the prenatal environment, since the events that may lead to leukemia are possibly initiated in utero. Leukemia is a very complex disease with multiple risk factors. What these findings show is that the nutritional environment in utero could be one of those factors."