Vitamin D is widely recommended for bone and muscle health, and deficiency is common in seniors due to less sun exposure and reduced skin synthesis with age. However, taking very high doses over time can lead to elevated calcium levels in the blood (hypercalcemia), which some people experience as muscle weakness, fatigue, or difficulty walking.
Research on supplementation shows mixed results: correcting a true deficiency often supports better muscle function, but excessive intake does not always improve leg strength and may carry other considerations. The safe upper limit for most adults is generally around 4,000 IU per day, though your doctor may recommend testing your levels first.
What the Science Suggests About These Vitamins and Muscle Function
