Diabetic Aidan Fenton, 7, died at the Hurstville Ritz hotel in Sydney's west last April having attended a week of courses run by the "self-healing" proponent Hongchi Xiao.

Police questioned, then released, Mr Xiao after the death, which remains the subject of an ongoing investigation by Australian detectives. He has since continued to hold classes around the world to promote paidalajin, a therapy based on fasting, stretching and slapping that bruises patients.

Danielle Carr-Gomm, a 71-year-old diabetic, died suddenly on October 20 during a weekend retreat run by Mr Xiao in south-west England.

"I am certain that if she hadn't gone on this course, she would still be alive today," her son, Matthew, told British media.

Police said they had arrested a 64-year-old woman and two men, aged 53 and 51, on suspicion of manslaughter. The suspects are now on bail until mid-January, a spokesman said.

"You have to be hard a little bit, cruel a little bit, but not too much," Mr Xiao said when describing paidalajin in a video earlier this year.

On his YouTube channel and blog, he claims slapping the skin stimulates heat that dissolves toxins, treating everything from itchiness and baldness to lung cancer and Parkinson's disease.

"I'm not a doctor, I'm not a healer," Mr Xiao told ABC radio in March 2014 when he visited Australia. "I just teach you a way. Then you do it all by yourself. Slapping is easy. Stretching is just lying down on a bench."

Aidan Fenton, a year 1 student from Prospect in Sydney's west, attended an $1800 paidalajin workshop at the Healthpac Medical Centre in Hurstville. He was found unconscious in his hotel room on April 30 last year and could not be revived.

"NSW Police has compiled a comprehensive brief of evidence in the relation to the death, which included advice from the Office of the Director of Public Prosecutions," a spokesman said on Tuesday.

The police have investigated Mr Xiao as well as Aidan's parents, Geoff and Lily, but have not laid charges.

Mr Xiao extended his condolences to Aidan's family on Facebook last May while rejecting accusations he was a killer or conman.

In the same post, he extolled the effect of paidalajin on diabetes, linking to a "strictly controlled" study by an Indian hospital.

"[Type 1 diabetes patients] recorded improvements in their clinical condition," the study said. "However, during the Healing crisis and fasting when their blood sugars went up their [sic] needed medical support in the form of calories, fluids and rapid action insulin to prevent ketoacidosis."

Ketoacidosis is a potentially deadly condition caused by insulin problems.

"For children over three years old, in addition to slapping along the entire spine, slap the universal regions (elbows, knees, hands and feet), the entire four limbs, and stretch on a Lajin bench," Mr Xiao's website recommends.

It suggests fasting for three to four days during the practice.