The BBC's Daniel Sandford: "Manufacturers say the extra iron helps with growth and mental development"

A study of almost 500 babies found no evidence to support manufacturers' claims that formula milk improved the health of babies aged nine months and over.

Increasing numbers of parents are turning to costly "follow-on" milks fortified with iron when breastfeeding ends at about six months.

Iron deficiency, or anaemia, has been associated with developmental delays.

Author of the report Professor Terrence Stephenson talks about his findings

But the study, published in the British Medical Association's Archives of Disease in Childhood, concluded there was "no clear evidence" of any health benefit.

Nine-month-old babies were given either cows' milk, a low iron, or a high iron formula feed until they reached 18 months of age.

Their physical growth and mental development were then measured.

Similar development

Judy More says children get enough iron from other sources

The results showed that, while the children fed the iron-fortified formula had higher stores of iron in their blood, their development and growth were no different from those fed cows' milk alone.

The researchers, led by Dr Ruth Morley of the Menzies Centre for Population Health Research in Tasmania, concluded: "Our data do not support a routine need for supplementation in children between 9 and 18 months, or feeding formula rather than cows' milk."

Most mothers either breastfeed or use regular formulas until six months, but many switch to "follow-on" milks with added iron until their baby is at least a year old and often up to the age of two.

Judy More, from the British Dietetic Association, said: "Follow on formula can be used from six months if a mother wishes, but normally a baby will get enough iron from their weaning diet."

The Department of Health said breast millk is best, but iron-enriched formula is acceptable after six months. Cows' milk should only be given after 12 months.

Infant formula manufacturers issued a statement, which said: "There have been numerous studies demonstrating the benefits of feeding iron fortified formulas instead of cows' milkto reduce te risk of iron deficiency and anaemia."