Has your teenage daughter really got maths phobia - or is her problem actually iron deficiency? "That adolescent girls show a lack of interest in maths is always attributed to social and cultural factors. Those may be important, but iron deficiency may have a role in this," says Dr Jill Halterman from the University of Rochester's Children's Hospital at Strong, Rochester, New York.

Adolescent girls who are iron deficient are more than twice as likely to score below average in mathematics achievement tests than similar girls with normal iron levels. This finding holds up when race, poverty, ethnic background, possible lead poisoning and caretaker education are taken into account, and even if the girls have no obvious signs of anaemia.

Iron deficiency is relatively uncommon among children between the ages of six and 11, with less than 3 per cent being iron deficient, according to the study's findings. But starting at age 12, when many girls begin to menstruate, nearly one in 10 are iron deficient and about 3 per cent are anaemic. The more deficient the iron level, the lower the mathematics scores.