Hello Naomid,
I am taking locally produced Spanish collagen Ana Maria Lajusticia, which is in powder, and a daily dose of it 7,5 g contains 5,2 g of collagen, 227 mg of magnesium, 24 mg of vitamin C. I think that one can take any other type of collagen, but it is important that it is hydrolyzed (better assimilation) and probably better of animal origin. I just started, but a year before I took it for my arthrosis pains and it helped me. Collagen plays an important role in bone function, and it is not by chance one of the blood markers for osteoporosis and bone turnover is called procollagen type 1N terminal peptid (P1NP). It is discussed as well by Dr. McCormick. He suggests that this test should be taken after 3 months to see if your medicine works for you. Take care!