An increase in birth length by 2 cm is associated with a 9% increase in breast cancer risk, according to a study reported in PLoS Medicine, online. Isabel dos Santos Silva, MD, PhD, a professor of epidemiology at the London School of Hygiene and Tropical Medicine and colleagues, examined 32 studies involving 22,058 breast cancer cases.
The researchers found the strongest link between breast cancer and birth size occurred between a length at birth of greater than or equal to 50 cm. In addition to length, a 0.5 kg increment in birth weight, greater than or equal to 3.5 kg, was associated with an estimated 7% increase in the risk of breast cancer (PLoS Med 5: e193, 2008).
“Assuming causality, we estimated that about 5% of all breast cancers in developed countries could be attributable to high birth size,” the researchers wrote. They also said the association between birth size and breast cancer appeared to be largely independent of known risk factors.
“Further research is needed to unravel the biological mechanisms underlying the birth size-breast cancer association,” wrote Dr. Silva’s group.
In an accompanying editorial, Pagona Lagiou, MD, PhD, and Dimitrios Trichopoulos, MD, PhD, both from the epidemiology department at the Harvard School of Public Health in Boston, said while the relative size of the eff ects is small, the individual studies driving the conclusion were of sound epidemiological design. The research relied on objectively documented birth size parameters, allowing little room for bias (PLoS Med 5: e194, 2008).