Environmental factors like nutrition have a bigger effect on how children grow up to age five than genetics or ethnicity, according to a report released Thursday by the World Health Organization.

The global study tracked more than 8,000 children in six developed and developing countries from birth to age five.

Researchers used the data to develop a new tool that allows health practitioners and parents to see how kids measure up.

The previous growth chart used by Canadian doctors to measure infants and toddlers was developed in the U.S. in 2001, based on the average growth of a small sample of American children who were mostly bottle- fed.

"Children from India, Norway and Brazil all show similar growth patterns when provided healthy growth conditions in early life," the WHO said in issuing the new child growth charts.

"Differences in children's growth to age five are more influenced by nutrition, feeding practices, environment, and healthcare than genetics or ethnicity."

The findings mean when mothers are healthy and don't smoke, babies are vaccinated and given proper nutrition, kids everywhere can thrive and grow equally.

Bottle versus breast

The charts also reflect a difference in weight gain depending on how infants are fed, since bottle-fed babies tend to gain weight more quickly than breast-fed babies.

Breast-fed babies often came in underweight on the old charts, leading some doctors to suggest mothers switch to formula.

Under the new charts, slimmer babies who are breast-fed will become the ideal, and bottle-fed infants might be considered heavy.

Still, experts caution parents should never put any baby on a diet to lose weight.

"Because infancy is such a period of rapid growth and development, restricting nutrition would not be recommended," said Donna Secker, a registered dietician in Toronto.

The first set of growth charts include such indicators as:

  • Weight-for-age.
  • Length/weight for age.
  • Weight-for-length/height.
  • A body mass index standard for children up to age five.

The charts also include standards for developmental milestones, including standing, sitting and walking.