Hi Louise,
I'm not sure there is a definate answer to this yet?
I was diagnosed with RA a year ago. Information I've seen so far suggests a link with smoking and red meat, and possible response to a viral infection. But I too have never smoked & was not brought up in an environment where people smoked. I haven't eaten red meat since my teens.
There is a strong RA link in my family - on both of my parents sides. Both males and females affected with onset at varying ages. So the trigger remains a mystery to me. Hopefully research may soon be able to shed some light on this for us.
Sorry I'm not able to help
Good luck and best wishes,
Lottie