"The study shows abusive behavior is very common and not something doctors are regularly asking about and therefore finding," Claudia Cooper, a researcher at University College London, who led the study, said in a telephone interview.

A third of family caregivers said their abuse of the person they were looking after was significant, including frequent insulting or swearing, and half said they occasionally screamed or yelled at the person.

The researchers, who found few cases of physical abuse, say their study – published in the British Medical Journal – highlights the need for governments and health officials to widen efforts aimed at tackling elder abuse.

"This is the strongest evidence so far about the prevalence of abusive behavior from family carers of people with dementia," said Cooper.

"These were the sons and daughters, and husbands and wives."

An estimated 24 million people worldwide have the memory loss, problems with orientation and other symptoms that signal Alzheimer's and other forms of dementia – a number some researchers believe will quadruple by 2040.

With rising costs and under-pressure health care systems worldwide forcing many family members to provide their own care, the findings highlight the need to tackle abuse and register it is probably more widespread than thought, Cooper said.

The researchers surveyed 220 family caregivers of various socio-economic and ethnic backgrounds whose family members were recently referred to psychiatric services and living at home.