WEDNESDAY, Oct. 13, 2004 (HealthDayNews) -- Early growth patterns in a girl's life, going back as far as her birth weight, influence her later risk of developing breast cancer.
The findings essentially extend the stages of life that could be influencing a woman's chance for developing this disease.
"With respect to breast cancer, early life matters," said Dr. Mads Melbye, head of epidemiology research at Statens Serum Institute in Copenhagen, Denmark and a co-author of the study, which appears in the Oct. 14 issue of the New England Journal of Medicine. "This brings new clues as to where to focus our future research on this malignancy."
This study confirmed two previous findings: that extra height and high birth weight are risk factors for breast cancer, said Karin B. Michels, co-author of an accompanying editorial and an associate professor of obstetrics and gynecology at Harvard Medical School. The study also added a new finding: that rapid growth in childhood and adolescence increases risk.
All of this is part of an ongoing quest to explain the increase in the incidence of breast cancer in this country and others. "There's no question that there has been an increase in breast cancer in this country in the last 50 years, and we've definitely seen an earlier onset," said Dr. Benjamin Paz, medical director of the City of Hope Women's Health Center in Duarte, Calif. Genetics can explain only so much.
The authors of this study followed more than 117,000 Danish girls born between 1930 and 1975 to see whether growth patterns early in life influenced the risk of breast cancer in adulthood.
Using several measures of weight and height during childhood, they found that high birth weight, rapid growth around the time of mammary-gland development, high stature, and low body mass index at age 14 were all independent risk factors for breast cancer.
In addition, height at eight years of age and a rapid increase in height during puberty (8 to 14 years) were also associated with an increased risk for breast cancer.
Interestingly, age at first menstruation was not a risk factor in this study.
The relationships suggested here are not necessarily ones of cause and effect, Michels pointed out. "It could be that both these risk factors and the cancer are related to something like levels of insulin-like growth factor 1 or other growth factors," she said.
That would imply a role for diet and nutrition, especially as they relate to rapid growth during adolescence.
"We think the breasts of the girls who grew so fast seem to be exposed to higher concentrations of growth hormones, and that could potentially increase the risk for breast cancer. There could be similar mechanisms related to absolute height as well as birth weight," Michels said.
Growth hormones can be supplied by what we eat and, Michels said, "diet in our society has hanged over the past decade and maybe for the worse."
Researchers have observed that, in Japan, diet has changed, people are growing taller and the rate of breast cancer is increasing.
Although Melbye advised against using the data to change individual risk, the findings do not dispute one of the main health messages of the day: eat right and exercise.
Modifying diet may be one possible avenue by which to modify breast cancer risk. "To some extent, growth is genetically determined and there's nothing you can do about it," Michels said, but environmental factors also need to be explored. "It's one more reason to revisit the diet of our children, which is probably suboptimal at the moment."
"Healthy behaviors as a young person have a significant impact on the quality of your health as an adult," Paz added. "We need to spend more time educating our children at a very early age to adopt healthy behaviors. This is one more article that adds to the importance of what you do as a young adult."
More information
For more on breast cancer prevention, visit the National Cancer Institute.
