The Criminal Code's justification for physical punishment of children such as spanking should be removed, Canadian researchers say.

Monday's issue of the Canadian Medical Association Journal includes a paper reviewing how the understanding of the effects of physical punishment of children has shifted dramatically in 20 years.

Children who have experienced physical punishment tend to be more aggressive toward parents, siblings, peers and, later, spouses, and are more likely to develop antisocial behaviour, said Joan Durrant, of the department of family social sciences at the University of Manitoba and Ron Ensom of Children's Hospital of Eastern Ontario in Ottawa.

Physical punishment is also associated with a variety of mental health problems, such as depression, anxiety and use of drugs and alcohol.

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Pain from punishment could disrupt parent-child attachment, increase levels of the stress hormone cortisol or interfere with how the brain regulates stress, Durrant and Ensom suggested.

They noted that when parents in more than 500 families were trained to reduce their use of physical punishment, the difficult behaviours in the children also declined.

'Never spank' health message

The authors called on doctors to educate parents on child development to reduce angry and punitive responses to normal child behaviours and to provide resources on positive discipline.

Messages such as Toronto Public Health's "Spanking hurts more than you think" and the Public Health Agency of Canada's "Never spank!" should be reinforced.

"Physicians can urge the federal government to remove Section 43 from the Criminal Code, which provides legal justification for the use of physical punishment, thereby undermining public health initiatives," the authors concluded.

The Supreme Court of Canada ruled in 2004 that parents have the right to spank their children. But the country's top court also set out "reasonable limits."

Those limits include:

Spanking could be used against children between the ages of two and 12 years old.

Children could not be disciplined with an object.

Hits to the head would be unacceptable.

Spanking remains legally contentious in Canada.

The authors said that effective discipline depends on "clear and age-appropriate expectations, effectively communicated within a trusting relationship and a safe environment."

More than 400 organizations in Canada have endorsed the Joint Statement on Physical Punishment of Children and Youth, which encourages positive approaches to discipline and states that physical punishment of children and youth plays "no useful role in their upbringing and poses only risks to their development."