A swedish study published in 2013 ( http://archinte.jamanetwork.com/article.aspx?articleid=1568519 ) found that "men" taking excess Vit. C supplementation were twice as likely to form calcium oxalate stones. This is because excess Vit. C is partly excreted as oxalate. In contrast, in hypocitraturia , there is less citrate to bind to calcium ( calcium citrate is more soluble ) and so calcium binds to oxalate and precipitates.