Answers are grounded in this paper and cite their sources.
Food can be an excellent source of calcium. Dietary calcium is in general as well absorbed as calcium supplements, and exerts the same effects on bone. The main sources are dairy products, but also some vegetables and fruits contain considerable amounts of calcium. Mineral water can serve as a supplement. Cross-sectional, longitudinal and some interventional trials have shown positive effects on bone metabolism, bone density and bone loss. But the effect on fracture incidence is less certain, and that of milk, the most studied dairy product, still unproven.
No takes yet. Share an insight, caveat, or question.
P. Burckhardt (2015) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: