Why are vitamin D and calcium commonly emphasized together in adult bone health, and who are at higher risk of deficiency?

• A. Vitamin D improves calcium absorption and bone mineralization; higher risk: older adults, postmenopausal women, individuals with limited sun exposure.
• B. Vitamin D reduces calcium absorption; risk groups: children only.
• C. Calcium supplementation alone is sufficient for bone health in all, no Vitamin D.
• D. Vitamin D and calcium have no relationship.

Answer: (A)