MONDAY, Feb. 7, 2005 (HealthDay News) -- Women who were larger than average at birth have a sharply higher rate of breast cancer before age 50, a study by British and Swedish researchers suggests.

The study, of more than 11,000 babies born in Sweden in the first three decades of the 20th century, also found higher rates of digestive and lymphatic cancers in adults who were large for the time they spent in the womb.

It's unlikely that birth size for gestational age is a risk factor for adult cancers, the authors concluded. Rather, they suspect it may be a marker for some aspects of the fetal environmental that are related to risk. For example, larger birth size may indicate that a greater number of cells are at risk of cancer.

The study appears in the Feb. 7 online issue of the International Journal of Cancer.

Researchers have generally assumed that prenatal factors, such as birth weight, can influence cancer risk. But few studies have examined associations between birth weight and overall adult cancer risk, the researchers said.

The new analysis, while limited to data from one hospital, suggests that larger birth size is associated with increased risk of certain adult cancers.

"We have found some evidence supporting the hypothesis that larger birth size is associated with increased risk of certain adult cancers," the authors said in a statement. "However, our findings suggest that positive associations were not uniform across all cancer sites, but were particular to just a few sites."

To test possible links between birth weight and cancer, Valerie A. McCormack and her colleagues at the London School of Hygiene and Tropical Medicine and the universities of Uppsala and Stockholm examined detailed data on 11,166 babies born from 1914 to 1929 at Uppsala Academic Hospital in Sweden.

The researchers used a statistical method for scoring an infant's birth weight for its gestational age -- the time spent in the womb.

A total of 2,685 of those babies were later diagnosed with cancer during the follow-up period from 1960 to 2001.

But the researchers found the link between larger birth size was limited to certain adult cancers. Each increase in birth weight of about 15.87 ounces at 40 weeks' gestation was associated with a 17 percent increase in lymphatic cancers and a 13 percent increase in digestive cancers, including stomach, colorectal and pancreatic.

For women, a strong association was found between breast cancer under the age of 50 and larger birth size. Women in the highest category of birth weight -- 8.8 pounds or more -- were four times more likely to get breast cancer than women in the lowest category -- less than 6.6 pounds.

At the same time, women who were larger at birth had lower rates of endometrial cancer. Rates of this cancer among women in the highest weight category were almost half that of their counterparts in the smallest weight group.

Hoda Anton-Culver, chief of the epidemiology division at the University of California, Irvine, said the study authors are on the right track.

"I think what they've done here in this study is to show one more type of exposure and one more piece of the [cancer-risk] puzzle," she added.

In pregnant women, for example, scientists hypothesize that fetal exposure to estrogen increases a daughter's lifetime risk of breast cancer, all things being equal, explained Richard G. Stevens, a cancer epidemiologist at the University of Connecticut School of Medicine.

"Higher estrogen [exposure] tends to make the baby bigger, if it's a girl," he added. So if there's higher estrogen exposure, you would expect a baby to be larger. In that way, this study helps support the idea that birth weight is a marker for some underlying risk, such as fetal exposure to estrogen, he said.

"The significance of this [study] is to confirm our longtime hint or guess that estrogens have a lot to do with breast cancer," concurred Anton-Culver.

Although she said more research is needed to fully understand birth weight as a risk factor, she also added, "I think one can start looking at how we can start to control exposure to estrogens in women."

More information

Visit the American Academy of Family Physicians for more on assessing your risk of cancer.

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