Nick - Dogs produce vitamin C in their bodies (unlike human beings ). Healty dogs should not need supplemental vitamin C. If they get too much it will flush out via urine. As you do more research you'll find that there is a realtionship between HD & a deficantcy of Vitmin C, possibly cause & effect relationship. :?: I believe the improvemt in HD dogs given C is when the Vitamin C gets to the normal level for that dog. But it stops there, the HD relief is relative. I saw a major inprovement in an 11 yr. old Catahoula that bi-lateral HD, after being on ENP's Glucosamine + http://www.effectivenaturalpets.com/cluc-con.html I do not know if my dog was at proper levels of Vitmin C. I do feed BARF, with a big varity of Fruit & Veggies along with the Meaty Bones. Which Should supply enough Vitamin C. :?: