At the 10th annual conference of the American Institute for Cancer Research (AICR), Dr. Leena Hilakivi-Clarke, of the Lombardi Cancer Center at Georgetown University, outlined the increasing evidence that fetal and childhood diets may have a greater impact on lifetime breast cancer risk than diets during adulthood. Dr. Hilakivi-Clarke described her own work and summarized ongoing worldwide research efforts.
Previous research has linked diets that raise the levels of estrogen in the blood with an increased risk for breast cancer. The work of Dr. Hilakivi-Clarke and her colleagues, however, suggests that the link between estrogen and cancer risk is more complex than previously thought, and that a new variable—time of life—seems to play an important role.
“At certain stages of a woman’s life, particularly in the womb and after menopause, diets that induce high estrogen levels do indeed seem to increase her risk of getting breast cancer. During reproductive years, however, high estrogen levels show no effect at all,” said Dr. Hilakivi-Clarke.
Childhood Diet and Cancer Risk
She added that incoming laboratory and human studies now suggest that at still another time—childhood—high estrogen levels seem to play a powerful protective role against breast cancer. She reviewed the results of human trials that have linked certain traits associated with high estrogen levels during childhood (for example, high body mass and high-fat diets) to a lowered risk of developing breast cancer.
“These are surprising results,” Dr. Hilakivi-Clarke said, “because most of the scientific literature to date suggests that high-fat diets tend to raise breast cancer risk, not lower it. But it’s important to remember that research has only begun to study the importance of childhood diets on cancer risk.”
This new research suggests that early diets have a different, and possibly more central, effect on lifetime breast cancer risk than diets consumed at any other time of life. Dr. Hilakivi-Clarke cautions, however, that many variables remain to be studied before responsible dietary recommendations can be made.
Looking for Answers in Different Diets
In the meantime, Dr. Hilakivi-Clarke is attempting to understand the paradoxical effects of estrogen in early life by exposing laboratory rats to different dietary sources of estrogen during fetal life and early childhood.
She was motivated to follow this line of investigation because she suspected that the type of diet was key. “We know that Asian women, who consume high amounts of soy, have very low rates of breast cancer compared to Western women,” she explained. “When Asian women migrate to Western countries and consume typical Western diets, however, their breast cancer rates begin to rise. Among their daughters, in fact, a particularly sharp increase in breast cancer rates occurs.”
High Estrogen Levels During Fetal Life
Dr. Hilakivi-Clarke and her colleagues put pregnant rats on one of two food plans that raise fetal estrogen levels: a diet high in polyunsaturated fatty acids or a diet high in soy. A third group of rats received injections of genistein (a compound isolated from soy that acts as a weak estrogen in the body).
The offspring of rats on the fatty acid diet and of rats who received injections of isolated genistein showed an increased risk of breast cancer. “This is consistent with previous research showing that diets that raise estrogen levels during fetal life increase breast cancer risk,” Dr. Hilakivi-Clarke noted.
The offspring of rats who were fed soy diets, however, were no more or less likely to develop tumors than rats fed a normal diet. This was the case despite the fact that soy contains estrogen-like genistein (which tended to increase estrogen levels during pregnancy) and suggests that some other component within soy interferes with genistein’s estrogenic nature, keeping it from triggering the cancer process.
High Estrogen Levels During Childhood
Next, Dr. Hilakivi-Clarke and her colleagues studied the effects of genistein and another plant-based, estrogen-like compound called zearalenone on prepubertal rats. They found that either of these substances lowered breast cancer risk. These results were consistent with the risk-lowering effect that was seen in human studies, as well as in their laboratory studies on prepubertal rats exposed to estrogen.
Dr. Hilakivi-Clarke proposed that estrogen exposure during childhood may bring about changes in the number and type of hormone receptors, resulting in lowered lifetime cancer risk. She also said that the cells of the mammary gland itself seem particularly sensitive to the effects of estrogen during this stage of life. Thus, they are more likely to differentiate.
Cells that easily differentiate seem less likely to become cancerous. This is because the amount of time during which they are susceptible to spontaneous, uncontrolled growth (ie, cancer) is greatly reduced.
Never Too Late for Dietary Changes
Dr. Hilakivi-Clarke concluded her statements by stressing once again that although much of this new evidence was interesting and even surprising, the data were preliminary. “Even if it turns out that early diets exert the greatest influence on lifetime risk, the contributions of diet during adulthood are still considerable,” she said. “Everything we know says that it is never too late to take dietary steps that provide real protection.”
Evidence that healthy diets high in fruits, vegetables, whole grains, and beans offer overall cancer protection is “convincing and compelling,” according to the AICR report Food, Nutrition and the Prevention of Cancer: A Global Perspective. The AICR estimates that following such a diet, maintaining a healthy weight, and getting regular exercise could bring about an astonishing 30% to 40% drop in worldwide cancer rates.
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