BONNY babies who tip the scales at close to nine pounds when they are born run a greater risk of cancer in later life, according to new research.

A study relating birth weight to subsequent health suggests that women who are heavier as babies are four times more likely to develop breast cancer before the age of 50 than their lighter counterparts.

Researchers found that the occurrence of breast cancer was raised significantly for women born weighing more than 4kg (8lb 13oz) compared with those who weigh 3kg (6lb 9oz) or less at birth.

Similar trends were identified for digestive and lymphatic cancers among both sexes, while higher birth weights were found to protect women against endometrial cancer.

The study, initiated by Professor David Barker’s team at Southampton University, is the latest in a long line to examine the correlation of birth weight and health in later life.

Previous studies have tended to show that heavier babies do better, being less likely to suffer from heart disease or diabetes, for instance.

The research, backed by the Medical Research Council and led by Valerie McCormack, of the London School of Hygiene and Tropical Medicine, uses birth records collected in Uppsala, Sweden, between 1915 and 1929.

A total of 11,166 single births who were still alive in 1960 were followed up until 2001, by which time 2,685 had developed some form of cancer. By comparing the incidence of cancer with birth weights, it was possible to show some patterns.

For every 450g (1lb) increase in birthweight, the risk of lymphomas increased by 17 per cent, and stomach, colorectal and pancreatic cancers by 13 per cent. Some other cancers, including prostate, showed no effect. For all cancers taken together, in men every pound of weight at birth increased risks by 8 per cent.

In women, every extra pound increased risks by 24 per cent for the under-50s, but reduced risks by 3 per cent for the over-50s — because the additional risk of breast cancer is restricted to younger women.

Writing in International Journal of Cancer the team say that some of its findings may have arisen by chance, but it is plausible that the links between birth weight and adult cancer are related to some aspects of the foetal 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,” they say.

“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.”

Just why heavier babies should be more prone to certain types of cancer is not clear. But the most obvious possibility is that having a larger body, with more cells, exposes more of them to the risk of the kind of changes that lead to cancer.

Alternatively, high birth weight may be a marker for high levels of certain growth factors in the womb, which may in later life encourage the growth of tumours.

An interesting finding in the study is that there is no obvious link between the age of a mother and the risks of cancer in her children. The suggestion had been that declining egg quality in older women could increase cancers in their children, but the study found no such link, except for endocrine cancers.

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

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