"Her decision not take the drugs really stimulated me because I support evidence-based medicine."
However, once he started delving into the research behind the way osteoporosis was diagnosed and treated, he made some disturbing discoveries, he said.
His documentary, The Osteoporosis Story, challenges the way osteoporosis statistics are gathered, how the disease is diagnosed and the effectiveness of the drugs offered to women to prevent the development of the disease, but it ultimately questions the robustness of the evidence-based medical health system.
The documentary was based on Gillian Sanson's book The Myth of Osteoporosis, but it was the "why" and "how" that interested him, Mr Johnston said.
When people told him "80% of the medical information you receive comes from commercial sources, even though it doesn't appear that way", he wanted to know how that could happen.
The aim of the documentary was not to tell people what to do, but to give them enough information to make their own decision in consultation with their GP, Mr Johnston said.
"I want to encourage people to do things to take their own health seriously and, therefore, be more responsible for their own bodies. And that means digging out the information that you need to keep yourself healthy.
"You can't put your head above the medical parapet without being certain the information you have got is backed up by appropriate medical journals, so that is where we have gone."
A website set up to market the DVD, www.theosteoporosisstory.com, listed references used in making the documentary and would be updated with new information and research, he said.
However, the project is not one he expects to make money from and, after 30 years in the industry, this is the first time he has gone against advice given to every budding television producer to "never put your own money into a project".
"I would love to give it away free to anybody, but if we can recoup our production costs we will be happy."
Osteoporosis is a bone-thinning condition which can increase the risk of bone fractures.
