This phase is known as modelling, during which mineralisation or impregnation with calcium occurs. A calcium-rich diet and exercise are important in childhood, adolescence and early adulthood to maximise bone mass and strength. Bone strength and density start to deteriorate from about 35 years old. The osteoclasts, which resorb old bone, start to become more active than the osteoblasts which deposit new bone. The rate of rebuilding fails to keep up with the rate of breakdown, resulting in osteoporosis.
Large gaps appear in the trabecular bone as the honeycomb structure crumbles.
The denser cortical bone is also affected. Women are more at risk than men as they have smaller skeletons. They experience a five to ten-year period of rapid bone loss at the menopause due to a fall in oestrogen levels. This is followed by a less rapid phase of age-related bone loss which men also experience. Screening Men and women who have already had a fracture after a minor fall are at risk of having another one.