Epidemiologists at the University of Buffalo in the US said they had found that premenopausal women whose birth weight was greater than 8.5 pounds, and premenopausal women who had not been breast fed as infants, had an almost two-fold risk of developing breast cancer when compared to premenopausal women whose weight at birth was in the reference range of 5.5-7 pounds and who had been breast fed.
There was no association between birth weight and breastfeeding in infancy and postmenopausal breast-cancer risk, said the researchers at the American Association for Cancer Research annual meeting in Anaheim, California in April.
"The intrauterine and neonatal life periods have been suggested as critical windows in mammary gland development," said lead researcher Maddalena Barba.
"In utero and early childhood exposures might affect breast cancer risk by altering the hormonal environment of the developing foetus and young infant through mechanisms not yet completely clarified," she suggested.
Barba and colleagues analysed data collected from 2,382 women participating in the Western New York Exposures and Breast Cancer Study conducted from 1996-2001 during in-person, computer-assisted interviews.
Complete information on the exposures of interest was available for 845 participants newly diagnosed with breast cancer during the study period who served as cases, and for 1,573 matched controls.
Researchers compared cases and controls, taking into consideration already well-recognized breast-cancer risk factors such as age, education, body-mass index, history of benign breast disease, family history of cancer, months of lactation, age at first menstrual period, age at first pregnancy, number of pregnancies and age at menopause for postmenopausal women.
None of these variables showed a relationship with postmenopausal breast cancer. Birth order was not associated with breast cancer risk in pre- or postmenopausal women.
"Our results support the hypothesis that early life events impact women's breast-cancer risk later in life," said Barba. "Further research based on targeted studies is needed to reach a deeper understanding of the underlying biological mechanisms."