Has to do with how much phosphorus you consume. As you get older (middle age), your body gets less effective at breaking down these compounds, which apparently calcify (?) into toxic compounds. I'm by no means a biologist, but I've heard this from people who are. http://umm.edu/health/medical/altmed/supplement/phosphorus Not an issue in young people. I guess people who exercise a lot or are putting on muscle or are athletes probably shoot for around 100g, now that I think about it.
Hm, that's pretty interesting. The phosphorous:calcium ratio problem that your link addresses (too much phosphorous in the blood leaches calcium out of bones and into blood to maintain the proper ratio, this leads to weaker bones and additional calcification of soft tissues) brings to mind the problem with salt; it's not that additional sodium intake is necessarily unhealthy, it's that too much sodium can throw off your sodium:calcium ratio which can then cause the same kind of problems (plus higher blood pressure depending on the person and just how much sodium they're taking in and are able to process). Not something I'd heard about before. I did some reading after you mentioned risks of high protein, and while I didn't read about calcium I did read about cancer. More protein means more cellular growth and division, and more cellular growth and division means more risk of cancer. This, also, becomes more significant in older people. Seems like the best plan is to eat your protein and build your muscle when you're young and then cut down when you get a bit older.
This is also interesting, though of course it's a bit ... tautological, or self-defeating. That is, taken to extremes the "logical" conclusion would be no cell division at all. So I'd guess that shouldn't be a significant factor in an athlete's cost/benefit analysis. Maybe there's a defined amount of protein/day where the risk factors exponentiate, but I bet the science is as yet too imprecise to find it.I did some reading after you mentioned risks of high protein, and while I didn't read about calcium I did read about cancer. More protein means more cellular growth and division, and more cellular growth and division means more risk of cancer. This, also, becomes more significant in older people.