Vitamin D Deficiency: Subtle Clues Your Body Sends

Vitamin D functions more like a hormone than a conventional vitamin. It regulates calcium absorption, modulates immune response, and influences muscle function. Deficiency is remarkably prevalent — affecting an estimated 40% of adults in temperate climates — yet symptoms develop so gradually that many people never connect the dots.

How deficiency develops

Human skin synthesizes vitamin D upon UVB exposure. Reduced sun time, darker skin pigmentation, aging skin, sunscreen use, and geographic latitude all limit production. Dietary sources — fatty fish, fortified dairy, egg yolks — rarely supply sufficient amounts alone. Obesity sequesters vitamin D in adipose tissue, lowering bioavailable levels.

Symptoms clinicians see most often

• Proximal muscle weakness, especially difficulty rising from a seated position
• Diffuse bone pain or tenderness, particularly in the pelvis and lower back
• Recurrent upper respiratory infections in otherwise healthy adults
• Low mood during winter months that improves with spring sunlight
• Hair shedding beyond normal seasonal variation

Severe or prolonged deficiency in children causes rickets; in adults it contributes to osteomalacia and accelerates osteoporosis progression.

Testing and supplementation

Serum 25-hydroxyvitamin D is the standard diagnostic test. Levels below 20 ng/mL indicate deficiency; 20–30 ng/mL suggest insufficiency. Treatment typically involves cholecalciferol (D3) at doses determined by severity — often 1,000 to 4,000 IU daily for maintenance after repletion.