What causes vitamin d deficiency?

Vitamin D is an important nutrient that plays several critical roles in your body, including bone health and immune support. You need vitamin D to absorb calcium and phosphate for healthy bones, muscles, nerves, and tissues. You typically get it from your diet and sun exposure.

If you are not getting or absorbing enough vitamin D, it can negatively impact your health. Here are common causes, symptoms, and treatments for deficiency.

Causes of vitamin D deficiency

• Diet low in vitamin D–rich foods (fortified dairy, orange juice, cereals; fatty fish; cod liver oil; egg yolks)
• Lack of sunlight exposure (indoor lifestyle, night work, sunscreen, pollution)
• Darker skin pigment (higher melanin reduces vitamin D synthesis)
• Age (reduced skin synthesis and kidney conversion in older adults)
• Breastfeeding without supplementation (infants need 400 IU/day)
• Malabsorption conditions (celiac disease, Crohn’s, cystic fibrosis, ulcerative colitis)
• Liver or kidney disease (impairs activation of vitamin D)
• Gastric bypass surgery (bypasses absorption sites)
• Obesity (vitamin D sequestered in fat cells)
• Certain medications (carbamazepine, cholestyramine, steroids, nifedipine, rifampin, phenobarbital)

Symptoms of vitamin D deficiency

• Bone pain
• Muscle weakness, aches, or spasms
• Fatigue
• Tingling or “pins-and-needles” in hands or feet

Severe deficiency can lead to low calcium and phosphorus absorption, triggering secondary hyperparathyroidism and bone density loss, increasing risk of fractures, osteomalacia, and rickets in children.

Diagnosis

Measured by the 25-hydroxyvitamin D blood test (25(OH)D), the main circulating form of vitamin D.

Treatment

Treatment aims to restore and maintain normal levels. Your provider may recommend:

• Vitamin D supplements (D2 prescription or over-the-counter D3)
• Calcium supplements if calcium is low
• Phosphate supplements if phosphate is low

Dosage and form depend on individual needs and underlying conditions.

Risks of supplementation

Excess vitamin D from supplements can cause toxicity: nausea, vomiting, appetite loss, constipation, confusion, muscle weakness, kidney stones, kidney damage, and high blood calcium leading to arrhythmias and kidney failure.

Sources

• Vitamin D: Fact sheet for health professionals. Office of Dietary Supplements, NIH. Accessed May 18, 2025.
• Kaur J, Khare S, Sizar O, et al. Vitamin D Deficiency. StatPearls. Updated Feb 15, 2025. Accessed May 18, 2025.
• Vitamin D Deficiency. Merck Manual Consumer Version. Last updated Sep 2024. Accessed May 18, 2025.