Johns Hopkins team determines that calcium is risky, and does not improve bone density:
10 years of research failed to produce any substantiation of the meme, “calcium makes strong bones.” In fact, though I hear people parrot this television advertisement quote and others like it all the time, I’ve never found any legitimate science to support it. Moreover, expert consensus from the International Osteoporosis Foundation officially declared that protein sufficiency and super-sufficiency plays a far more vital role in bone health: https://link.springer.com/article/10.1007/s00198-018-4534-5
This makes more sense, as 50-60% of bone volume is comprised of protein. The entire 100% structural matrix of bone is protein. When people were/are declaring milk the champion of bones, it’s rather odd that they hone in on the measly 300 milligrams of calcium in a cup of milk instead of the massive 9,000.00 milligrams of protein in the same cup. This says nothing of the fat soluble vitamins (which support bone health) we find in full fat dairy but don't find in reduced fat dairy.
More importantly, the societal fervor over calcium appears to increase risk of plaques and heart disease. Without fat soluble vitamins to direct calcium, there is no biological reason to believe calcium alone is beneficial. Calcium is a building block for atherosclerotic plaque buildup. Undirected in an unhealthy body, calcium is risky.
The central thesis of the promoters of milk was always on shaky ground. In every large observational study, milk consumption had no association with improved bone density (https://pubmed.ncbi.nlm.nih.gov/9224182/), and when researchers controlled for other variables, milk consumption from age 20 and on is associated with INCREASED risk of hip fracture (https://pubmed.ncbi.nlm.nih.gov/8154473/ ). In global epidemiological research, we also find women in other societies with incredibly low incidence of osteoporosis have zero milk consumption. For a time, the crunchy granola community honed in on the "acid load" in milk to try to undermine it; but they weren't playing with a full deck, as protein is made of amino ACIDS, and the amino ACIDS are some of the only things right about milk. They were moving toward the right stance, but for the wrong reasons. Meanwhile, the general populace who believes in milk has the wrong stance and no reasons. So, maybe we should focus on the science instead of the slick marketing memes.