Larger newborn girls are more likely to develop breast cancer in adulthood than smaller ones, UK research suggests.
Researchers found that for every 0.5kg increase in birth weight, the risk of developing breast cancer rose by 7 per cent.
Previous research into the association between birth size and breast cancer has produced mixed findings.
This latest study is a re-analysis of 32 published and unpublished studies involving 22,058 women with breast cancer and 604,854 healthy women who did not have cancer.
Information on birth size was based on birth records that included measurements of weight, length and head circumference.
After adjusting for other risk factors, a heavier birth weight was associated with an increased risk of breast cancer.
Birth length and head circumference were also positively associated with increased breast cancer risk.
For every 2cm increase in body length, the risk of breast cancer increased by 6 per cent.
Lead researcher Professor Isabel dos Santos Silva, from the London School of Hygiene and Tropical Medicine, said: 'Birth size is a predictor of adult height which has been shown to increase the risk of breast cancer, so this may be the reason behind the link.'
It has also been proposed that the maternal and foetal environment associated with large birth size may alter the development of the breast, making it more susceptible to cancer later in life.
'Further research is now needed to unravel the biological mechanisms underlying the birth size-breast cancer association,' added Professor Silva.
PLOS Medicine Online 2008.
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