In 2015, the British Medical Journal published a high quality meta-analysis (review of 51 studies!) on calcium intake, supplemental or dietary, and its effect on bone mineral density. The conclusion: Increasing calcium intake from dietary sources or by taking calcium supplements produces small non-progressive increases in BMD, which are unlikely to lead to a clinically significant reduction in risk of fracture (PMID: 26420598).
Osteoporosis is defined as low bone mineral density. However, this is not simply a deficiency of calcium. The bigger issue is sedentary lifestyle. If you are not using your bones, you are losing your bones. Bones feed themselves via compression and decompression forces, imagine a sponge being compressed down into a puddle. Weight bearing exercises are recommended, however without proper form and appropriate weight this can lead to injury.
Two under-utilized exercises that are great at feeding the bones are Jump-rope and trampoline jumping. Jump rope offers the body an abundance of compression forces. Trampolining offers a nice balance of compression and decompression. You can find a small indoor mini trampoline with a safety bar, known as a rebounder. A great exercise to do while watching TV, an exercise that may be slightly nostalgic to your childhood.
These exercises also promote lymphatic movement, which is great for detoxification. Moderate running or jogging can also be considered a great exercise to build strong bones! The key is moderation, some cases of osteoporosis are so severe that the idea of jumping rope and/or running is dangerous. Consult with your qualified healthcare practitioner what is safe and effective for you.