Overview

• Vitamin D is crucial for calcium and phosphate metabolism, supporting bone strength, muscle function and immune health, with most supply generated by sun exposure between March and October
• Dietary sources like fatty fish, egg yolks and fortified foods account for only about 10–20 percent of daily vitamin D needs
• Health authorities set an adult reference intake of 20 µg (800 IU) per day and a tolerable upper limit of 100 µg to prevent toxicity
• People with limited sun exposure, darker skin, chronic gastrointestinal, liver or kidney conditions should measure their vitamin D levels before considering supplements
• Excessive supplementation can trigger hypercalcemia, nausea, kidney damage and heart rhythm problems, so long-term use should be supervised by a physician