Parents who smack their children could be putting them at higher risk of cancer, heart disease and asthma.
Harsh punishment in childhood – including shouting – increases the risk of disease in later life, according to psychologists from Plymouth University.
In research published in the prestigious Journal of Behavioral Medicine, they say that harsh punishment causes stress, and the increased stress may then cause biological changes. Professor Michael Hyland, from the university's School of Psychology, led the study. His team asked 700 people in Saudi Arabia – where smacking children is considered acceptable – about their upbringing.
The study, conducted by Professor Hyland and colleagues Dr Ahmed Alkhalaf and Dr Ben Whalley, included 250 healthy people and 150 patients with asthma, cancer or cardiac disease.
The researchers asked whether people had been physically or verbally abused as children. Patients with asthma, cancer and cardiac disease were significantly more likely to say they had been, compared with the 250 healthy subjects.
Professor Hyland said: "Early life stress in the form of trauma and abuse is known to create long-term changes that predispose to later disease.
"But this study shows that in a society where corporal punishment is considered normal, the use of corporal punishment is sufficiently stressful to have the same kinds of long-term impact as abuse and trauma."
Participants were asked whether, and how often, they had been physically or verbally punished as children. Those who had cancer were 1.7 times more likely to have been beaten as a child compared to the healthy sample. Those with cardiac disease were 1.3 times more likely and those with asthma 1.6 times more likely to have been beaten.
Professor Hyland, who teaches health psychology at the university, said: "Our research adds a new perspective on the increasing evidence that the use of corporal punishment can contribute to childhood stress. When it becomes a 'stressor', corporal punishment contributes to poor outcomes both for the individual concerned and for society."
Corporal punishment was first banned in the home and school by Sweden in 1976, and another 30 countries have followed.
In many countries, including the UK, corporal punishment is illegal in schools but not in the home.
In some countries, such as the United States, there is no universal ban on corporal punishment in schools.
Although the use of corporal punishment for children has decreased, about half the world's children are still thought to be beaten.
Councillor Nicky Williams, Plymouth City Council cabinet member for children and young people, said: "It's not up to me to dictate to parents what they do in their own homes.
"At the council we take seriously any act which causes stress and harm to children. But this is about how far the State should get involved in people's lives.
"This isn't something where I believe the council has a role to wade in – but we do have to keep children safe."
She said other factors like cigarette smoke probably caused even more harm.
In a survey on the parents' social network Mumsnet, 52 per cent of the 1,092 people who responded said they had never smacked their children.
Only 35 per cent supported the idea of a total ban, 54 per cent opposed a ban and 11 per cent were undecided. Only half of those who had never smacked their own children backed the idea of a total ban.
In Britain, smacking a child sufficiently hard to leave a mark can lead to a criminal prosecution with a maximum five-year prison sentence.