An elderly person has a diet that is low in calcium and vitamin D. Explain why this may cause problems with their bones and muscles.

Calcium is a key component of bone mineral, giving bone its hardness and strength. A diet low in calcium means the body cannot maintain the mineral content of bone, so the skeleton becomes weak, brittle and more likely to fracture.
Vitamin D is required for the absorption of calcium in the small intestine. Without sufficient vitamin D, calcium uptake is reduced, further lowering bone calcium stores.
Calcium ions are also essential for muscle contraction. A deficiency therefore reduces the amount of calcium available for muscle cells, leading to muscle weakness, cramps and impaired function.