Former Boxer Mia St. John on Sobriety and New Purpose After Son's Suicide: He's 'Cheering Me On'

Mia St. John, a former boxing champion, has set out to help others with their mental health struggles after the death of her son, Julian

Mia St. John. Photo: Yuri Hasegawa

Former boxer Mia St. John has spent much of her life fighting for herself, but now, she's fighting for others.

The 54-year-old five-time World and International Boxing Champion is sharing the ups and downs of her life in her new memoir, Fighting for My Life, out Tuesday.

The book, co-written by PEOPLE's Elaine Aradillas, details her experiences growing up in Northern California, where she learned to fight after being bullied in grade school. Mia later struggled with drug addiction for most of her teenage years but eventually turned to martial arts and boxing, which helped her stay sober.

While she found success in the ring, Mia's situation at home was more challenging. Her son, Julian, who she shared with former husband Kristoff St. John, the late star of The Young and the Restless, developed paranoid schizophrenia when he turned 18.

"They won't give you a diagnosis until you're 18. But I had a sense," Mia tells PEOPLE in this week's issue. "And with my psychology experience in school, I knew the symptoms of schizophrenia. So I had a fear growing in me that this was schizophrenia. And he was eventually diagnosed with schizophrenia, but I already kind of knew."

The mental disorder can cause delusions and hallucinations, and a general lack of ability to function normally, according to Mayo Clinic.

His health battle was made worse after Julian also began using meth, Mia says. Julian was placed into rehab and underwent psychiatric treatment and eventually died by suicide at age 24 while at the facility.

Kristoff, who Mia describes as the "love of her life," died in Feb. 2019. It was later determined that his death was caused by heart disease, which was exacerbated by alcohol use.

Mia St. John and her son Julian in 2013. Courtesy

After the deaths of Julian and Kristoff, Mia found a new mission, in part pushing California mental health facilities to ban plastic bags in mental health wards to prevent suicides. She also started the Mia St. John Foundation (El Saber Es Poder), which focuses on helping people experiencing mental illness, homelessness, addiction and poverty.

For more on Mia St. John, pick up the latest issue of PEOPLE, on newsstands Friday, or subscribe here.

"I knew that I had a voice," she says of using her platform. "I was born to make a change, to make it a better system, to save children's lives, to help them. That's why in my foundation, a lot of the programs are to help kids like my son: young adults who suffer from mental illness, homelessness, and addiction."

Mia St. John with her family in 1993. Courtesy

She continues, "Hopefully the book will help others. I have a voice and I can help people. That was my true purpose in life. That's what I was born to do, was to help others."

Mia also joined Step Up on Second, an organization in Santa Monica, California, that helps people and families who are coping with mental health problems.

She hopes her efforts can hopefully save the life of someone who needs help, and she believes Julian would be "cheering me on."

"My son didn't want to die," Mia says. "I think that you're just struggling and you don't know how to get out of it. You don't see a way out. But you don't really want to die, you just want a way out."

Fighting for My Life is available to purchase now.

Updated by Sandra Sobieraj Westfall