Fruit and vegetables eaten before pregnancy lowers risk of leukemia

A new study led by researchers at the University of California, Berkeley, suggests that women who eat more vegetables, fruit and foods containing protein before pregnancy may have a lower risk of having a child who develops leukemia, the most common childhood cancer in the United States.

The study, published in the August 2004 issue of Cancer Causes and Control, is the first time researchers have conducted a systematic survey of a woman's diet and linked it to childhood leukemia risk.

The 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, which is part of the Northern California Childhood Leukemia 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, the 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.

"Fetal exposure to nutritional factors has a lot to do with what mom eats," said Christopher Jensen, a nutritional epidemiologist at UC 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.

Although the researchers only surveyed the foods eaten in the year before conception, they point to studies showing that dietary patterns remain stable throughout the pregnancy.

"The general habits of what you like and don't like to eat are not likely to change during pregnancy," said study principal investigator and co-author Gladys Block, UC Berkeley professor of epidemiology and public health nutrition. "If you hated liver before you got pregnant, you'll probably hate liver while you're pregnant."

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.

"This finding is consistent with research about the benefits of a diet high in fruits and vegetables in preventing adult cancers," said Block. "The positive message here is that mothers may be able to transfer some of those benefits to their children."

The researchers also studied the use of vitamin supplements, but did not find a statistically significant link to childhood leukemia risk.

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 Block. "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.

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.

A growing number of scientists believe that genetic changes linked to cancer later in life begin in the womb. Prior studies on children diagnosed with leukemia have found that blood samples taken at birth tested positive for the same genetic markers that were later found in the cancer.

"It goes back to the old saying to expectant mothers, 'You're eating for two,' " said Patricia Buffler, study co-author, UC 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."

Other co-authors of the paper are Xiaomei Ma at the Yale University School of Medicine, Steve Selvin at UC Berkeley's School of Public Health and Stacy Month of Kaiser Permanente in Oakland, Calif.