Soy Milk and Cow Milk

Just now I went to Giant Market and get some groceries. I notice that the price of cow milk has increased like 10% compare to 2-3 months ago. I don't know why but it seems that the price difference between cow milk and soya milk is getting bigger. Base on my last year observation, the price of soya milk and cow milk is very close to each other back then; but now the gap is getting bigger and bigger, soy milk seems relatively cheaper now.
A Taiwanese friend of mine was telling me that cow milk is for cow, according to what she said, cow milk is not so suitable for human being, milk producer just exaggerately claimed that milk is good for bones this and that but in fact it is just drain the bones faster, thus, it is better to drink soy milk. She even forward the email to me. Well, due to this reason, I bought four 1-litre packet of Soy milk. But then, my friend also warned me not to drink too much soy milk or else it will cause pain to the joint. So I can only drink it once in a while instead of everyday.