What is Vitamin D Deficiency?

Vitamin D deficiency occurs when the body does not have enough vitamin D to maintain healthy bones, muscles, and overall function. Vitamin D is essential for absorbing calcium and phosphorus—two minerals critical for bone strength. Without adequate vitamin D, bones can become thin, brittle, or misshapen, leading to conditions such as rickets in children and osteomalacia in adults.

Causes

Vitamin D deficiency can result from several factors, often overlapping:

  • Limited sun exposure – The skin produces vitamin D when exposed to sunlight. People who spend little time outdoors, live in northern climates, or consistently use sunscreen may not make enough.

  • Skin pigmentation – Darker skin contains more melanin, which reduces the skin’s ability to produce vitamin D from sunlight.

  • Age – Older adults produce less vitamin D in the skin and may also absorb less from food.

  • Dietary insufficiency – Few foods naturally contain vitamin D. People who avoid fish, dairy, or fortified foods may not get enough.

  • Medical conditions – Disorders like Crohn’s disease, celiac disease, or cystic fibrosis can impair absorption.

  • Obesity – Vitamin D can become trapped in fat tissue, making it less available to the body.

  • Medications – Certain drugs (e.g., steroids, seizure medications, cholesterol-lowering agents) interfere with vitamin D metabolism.

Symptoms

Vitamin D deficiency can be subtle, and some people may have no symptoms. When present, signs may include:

  • In children:

    • Bowed legs or bone deformities (rickets)

    • Delayed growth

    • Muscle weakness or pain

  • In adults:

    • Bone pain or tenderness

    • Muscle weakness, cramps, or aches

    • Fatigue and low energy

    • Mood changes, including depression

    • Increased risk of fractures due to weakened bones

Diagnosis

Diagnosis is typically made through:

  • Medical history and risk assessment – Reviewing sun exposure, diet, and health conditions.

  • Physical exam – Checking for bone tenderness, muscle weakness, or skeletal changes.

  • Blood test – Measuring 25-hydroxyvitamin D (25(OH)D), the most accurate indicator of vitamin D status.

Treatment

Vitamin D deficiency is highly treatable. Options include:

  • Dietary changes – Eating more vitamin D–rich foods such as fatty fish (salmon, mackerel, tuna), egg yolks, fortified milk, cereals, and orange juice.

  • Supplements – Vitamin D2 (ergocalciferol) or D3 (cholecalciferol). D3 is generally better absorbed.

  • Safe sun exposure – Short, regular periods of sunlight on the skin can help boost vitamin D levels, though sunscreen use and skin cancer risk must be considered.

  • Lifestyle adjustments – Maintaining a healthy weight and managing chronic conditions that affect absorption.