I would say, surprisingly often.

A gluten-free diet resolved conditions I thought would be forever undiagnosed and untreated, but this was after a long history of abdominal pain and a recent severe outbreak of dermatitis herpetiformis. My mother took up the diet too, and experienced significant heel spur relief -- her symptoms seemed totally atypical to me, but I can't argue with results. (Later investigations turned up a possible gluten/celiac-related calcium problem.)

It's relatively *common* for people who do not/may not have celiac disease to report health improvements from adopting a family member's new gluten-free diet (sorry, lost the source and short on time).

If you don't already have this link, please do. I think it's the most important dietary and celiac disease-related tool at my disposal.