The research focused on two national groups of people born in 1958 and 1970 in Great Britain, who were monitored by questionnaire at the ages of 26 and 33. Handedness was determined from hand preference for writing and foot preference for kicking a ball at the age of either 7 or 10.

In total, around 17,000 people were included in the study. Significantly, more men than women were left handers, but gender was not itself associated with increased risk of inflammatory bowel disease (IBD). But later birth was, with those born in 1970 more likely to have IBD than those born in 1958.

Altogether, 71 people had either confirmed Crohn's disease or ulcerative colitis, with left handers more than twice as likely to be affected overall. A similar pattern was found for Crohn's disease and ulcerative colitis when the two diseases were looked at separately.

Left handedness has been linked with various autoimmune diseases, including asthma, migraine, autism and diabetes, but so far, no one has been able to pinpoint why.

The authors point to previous research showing a seasonal variation in the birth of left handed girls, which, they say, might implicate some environmental factor.

Another, somewhat controversial, explanation is the amount of testosterone a fetus is exposed to in the womb, which may affect brain and immune system development.

(Reference: Inflammatory bowel disease and laterality: is left handedness a risk? Gut 2001; 49: 199-202)

12-Jul-2001