Children are presenting to hospital with anorexia nervosa at an earlier age and the condition is affecting an increasing number of boys, a new Irish study has found.

According to researchers, anorexia is a serious mental health illness that is best treated in the community. However if a person's weight reaches a critically low level, they will require hospitalisation.

The 2002 Census estimated that some 2,400 teenage girls were affected. The average age of onset among them was 14. However other than this, there is very little published Irish data on the condition, so the researchers decided to investigate further.

They looked at all inpatients admitted to Temple Street Children's Hospital with anorexia between 2005 and 2011.

They found that the average age of onset of the condition was 13.5 years, six months younger than the 2002 figures - this indicates that anorexia is presenting at an earlier age.

All of the patients came into hospital via the emergency department (ED). Almost two in three were self-referred, while the rest were referred by a GP.

Boys accounted for almost one in three admissions. However on admission, girls were found to be more underweight than boys even though they tended to present to hospital sooner than boys.

The most common features of the illness after low weight were over-exercising and food restriction. One in four patients were also known to have been vomiting. All of the girls who had reached puberty had amenorrhea (an absence of menstrual periods).

Overall, the hospital noted a big increase in the number of children presenting with anorexia over the last 10 years and this mirrors UK figures.

The high number of boys presenting is also in line with recent research which indicates a higher prevalence among males.

The fact that girls tend to present to hospital sooner suggests that there is better awareness and detection in girls.

The researchers expressed concern that ‘the overall mean age of onset was estimated at six months prior to seeking treatment'. They pointed out that the longer it takes to get treated, the worse the prognosis.

Early detection and treatment within the community is more preferable to hospitalisation later, they said.

Meanwhile, the study also noted that the average length of stay in hospital is over five weeks. This is expensive and requires many resources, such as specialist staff training.

The researchers added that the increase in children presenting with anorexia has important implications for community and hospital services. They emphasised that the new national children's hospital, which is to be built on the grounds of St James's Hospital in Dublin, will require dedicated beds and specialist staff to deal with this serious issue.

Details of these findings are published in the Irish Medical Journal.