The time of year in which a person is born may somehow sway the risk of developing brain cancer in adulthood, new research suggests.

If confirmed by further studies, the findings would indicate that some as yet unknown factors before or soon after birth contribute to brain cancer development decades later, according to the authors.

Their study of brain cancer patients and cancer-free adults the same age found that the risk of developing the disease appeared highest for people born in January or February and lowest for those born in July or August.

And for reasons that are unclear, the association between birth season and cancer risk was most pronounced among people who were left-handed or ambidextrous - with those born in the late fall through early spring having a greater risk.

However, the researchers stress that left-handed winter babies should not find the study results alarming. For one, it’s possible that the associations were simply due to chance, lead author Dr. Alina V. Brenner of the National Cancer Institute, Bethesda, Maryland, told Reuters Health.

The aim of the study, the researcher explained, was to unearth possible new clues about the causes of brain tumors - something that scientists currently know little about.

If the association between birth season and brain cancer risk is real, then researchers could investigate the factors that operate during pregnancy and early infancy and vary by season. Some “candidate” factors, according to Brenner and her colleagues, include infections, maternal diet, environmental toxins and hormonal influences during pregnancy.

But, Brenner noted, too little is known to tell which, if any, of these factors could be at work. It is also unclear what the crucial point in pregnancy might be.

The study, published in the journal Neurology, included 686 brain cancer patients from three U.S. hospitals and 799 “control” patients hospitalized for non-cancerous conditions. It is one of a number of studies that have tied disease risk to birth season.

For example, an “excess” of winter births has been found among children with brain cancer, and among people with conditions such as epilepsy, schizophrenia and bipolar disorder. Overall, birth season has been most strongly tied to diseases affecting the central nervous system, which is vulnerable to environmental insults during development.

As for why the association between birth season and brain cancer was stronger among lefties and ambidextrous people, there is no clear reason, according to the researchers. They included handedness in their analysis, in part, because handedness is thought to be influenced by prenatal and early-life factors that affect the central nervous system.

In addition, the researchers had, in a previous study, found evidence of a lower risk of brain cancer among left-handed people. Why those born in the winter might have a greater risk than their warmer-month peers is unknown.

SOURCE: Neurology, July 27, 2004.