Early Diet May Play Most Important Role in Breast Cancer Risk, Researcher Says

American Institute for Cancer Research
Thursday, 31 August 2000

Studies Suggest Pre-Natal, Childhood Diets Make the Difference

At the 10th Annual Research Conference of the American Institute for Cancer Research (AICR), a leading cancer scientist outlined the increasing evidence that fetal and childhood diets may have a greater impact on lifetime breast cancer risk than diets during adulthood. Dr. Leena Hilakivi-Clarke, of the Lombardi Cancer Center at Georgetown University, described her own work and summarized ongoing research efforts around the world.

Previous research has linked diets that raise levels of estrogen in the blood with increased risk for breast cancer. But the work of Dr. Hilakivi-Clarke and her colleagues 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 all-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.

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 (i.e., high body mass, high-fat diets) to lowered breast cancer risk.

"These are surprising results," she 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 is suggesting that early diet has a different, and possibly more central, effect on lifetime breast cancer risk than diet at any other time of life. But Dr. Hilakivi-Clarke went on to caution 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. 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 Linked to Greater Risk

Dr. Hilakivi-Clarke and her colleagues put pregnant rats on one of two food plans that raise fetal estrogen levels: a diet high in n-6 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."

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. This 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 Linked to Lower Risk

Next, Hilakivi-Clarke and her colleagues studied the effects of genistein and another plant-based, estrogen-like compound called zearalenone on pre-pubertal rats. They found that either of these substances lowered breast cancer risk. These results were consistent with the risk-lowering effect seen in human studies, and in their laboratory studies on pre-pubertal rats exposed to estrogen.

Dr. Hilakivi-Clarke suggested 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. They thus are more likely to differentiate.

Cells that easily differentiate - that is, embark upon the clearly defined biological process by which they assume pre-programmed forms and functions - seem less likely to become cancerous. This is because the amount of time during which they are susceptible to spontaneous, uncontrolled growth (i.e, cancer) is greatly reduced.

"It's Never Too Late" for Dietary Changes, Researcher Cautions

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. Everything we know says that it is never too late to take dietary steps that provide real protection."

Evidence that healthy diets high fruits, vegetables, whole grains and beans offer overall cancer protection is "convincing and compelling," according the AICR report Food, Nutrition and the Prevention of Cancer: A Global Perspective. In fact, AICR estimates that following such a diet, maintaining a healthy weight and getting regular exercise could bring about an astonishing 30 to 40 percent drop in worldwide cancer rates.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org