Birth size and adult cancer risk

Study shows larger babies have higher risk of certain cancers in adulthood

Babies who weighed more at birth had higher rates of digestive and lymphatic cancers in adulthood, according to a new study published February 7, 2005 in the online edition of the International Journal of Cancer, the official journal of the International Union Against Cancer (UICC). The study, available online at Wiley InterScience, also found that women who weighed more at birth had significantly higher rates of breast cancer before age 50, though much lower rates of endometrial cancer at all ages.

Medical experts have proposed associations between birth size and rates of adult cancer. To examine this hypothesis, researcher Valerie A. McCormack and colleagues at the London School of Hygiene & Tropical Medicine and the Universities of Uppsala and Stockholm investigated overall and site-specific cancer incidence in relation to birth characteristics in a Swedish population-based cohort.

The cohort included 11,166 babies born between 1915 and 1929 at Uppsala Academic Hospital in Sweden. At birth, detailed obstetric notes were taken on maternal age, gestational age, birth order, birth weight, placental weight, birth length and head circumference. Follow-up of the cohort was done through linkages to the Swedish Cancer Registry, national censuses and the Swedish Register of Deaths and Migration.

With 2685 people (24 percent) in the cohort diagnosed with cancer between 1960 and 2001, larger birth size was associated with an increased risk of certain adult cancers. A standard deviation increase in birth weight (which was 450g 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, though no association was seen between higher birth weight and five other non reproductive-related cancer sites.

Reproductive-related cancers accounted for nearly half of all cancer in women and nearly a third of all cancer in men. For women, a strong association was found between breast cancer in women under age 50 and larger birth size. Women in the highest category of birth weight (4kg or greater) were four times as likely to get breast cancer before age 50, compared with women in the lowest category (less than 3 kg). On the other hand, women who were large at birth were only half as likely to get endometrial cancer compared to their smallest counterparts. For men, the most common reproductive-related cancer, of the prostate gland, was analyzed but no association to birth factors was found.

While the researchers note that some of their findings may have arisen by chance, it is plausible that the associations between birth weight and adult cancer are related to some aspects of the fetal environment or the number of cells at risk of carcinogenesis. “We have found some evidence supporting the hypothesis that larger birth size is associated with increased risk of certain adult cancers,” the authors report. “However, our findings suggest that positive associations were not uniform across all cancer sites, but were particular to just a few sites. Furthermore, our findings generate the hypothesis, which merits further study, that rates of endometrial cancer are lower in women who had higher birth rates.”

Since previous studies have found associations between smaller birth size and increased risks of adult heart disease and diabetes, the authors conclude, “Both circulatory disease and cancer need to be considered in determining the net effect of prenatal influences on adult morbidity and mortality.”