Do bras prevent from getting saggy boobs?

I have big seize DD breasts and wear seldom a bra and they are still ok , not saggy and nice to look at , I get compliments from both male and female . I've heard repeatedly by women I know going without a bra cause them to get saggy , but it sounds like a product of confirmation bias to me. Is there supporting evidence for the claim that if you don't wear a bra you should expect saggier boobs at old age? My mom is 60 and has nice firm boobies and never worn a bra .. :)