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Vitamin D Deficiency

Brief Overview: Vitamin D deficiency occurs when serum vitamin D levels are insufficient to support normal bone health, calcium absorption, and other physiologic functions. Vitamin D plays a key role in bone mineralization, muscle function, immune regulation, and inflammation control.
Deficiency is common and often underrecognized, particularly in older adults, individuals with limited sun exposure, malabsorption, or chronic disease. Treatment is typically straightforward and effective with oral vitamin D supplementation.

Prevalence: According to UpToDate, “In the 2021 to 2023 survey, the prevalence in the United States of vitamin D <12 ng/mL was 5.5 percent, and for vitamin D of 12 to <20 ng/mL, 15.6 percent.”

Etiology: According to UpToDate, “There are several causes of vitamin D deficiency, including decreased intake or absorption, reduced sun exposure, increased hepatic catabolism, decreased endogenous synthesis (via decreased 25-hydroxylation in the liver or 1-hydroxylation in the kidney), or end-organ resistance to vitamin D.”

Risk Factors:

  • Older persons who are confined indoors (including those who are institutionalized or homebound)
  • Limited effective sun exposure
  • Osteoporosis
  • Hyperparathyroidism
  • Malabsorption
  • Chronic kidney or liver disease
  • Darker skin pigmentation
  • Obesity

Commonly Associated Conditions:

  • Osteopenia and osteoporosis
  • Increased fracture risk
  • Muscle weakness and falls
  • Secondary hyperparathyroidism
  • Chronic kidney disease
  • Malabsorption syndromes
  • Autoimmune and inflammatory conditions (association)
  • Depression and fatigue (association)

Common Medications:

  • Oral Vitamin D3 (cholecalciferol) – preferred over D2
  • Oral Vitamin D2 (ergocalciferol)

Common Labs, Imaging, and Tests:

  • Serum 25-hydroxyvitamin D (25[OH]D or calcidiol)
    • Vitamin D sufficiency is defined as a 25(OH)D concentration ≥20 ng/mL (50 nmol/L)
    • Vitamin D insufficiency is defined as a 25(OH)D concentration of 12 to <20 ng/mL (30 to 50 nmol/L)
    • Vitamin D deficiency is defined as a 25(OH)D level <12 ng/mL (30 nmol/L)
    • A "risk" of vitamin D toxicity is defined as a 25(OH)D level >100 ng/mL (>250 nmol/L) in adults ingesting substantial amounts of calcium
  • Serum parathyroid hormone (PTH)
  • Serum calcium, phosphorus, and alkaline phosphatase
  • DEXA scan
  • Renal function tests if kidney disease present

Common Symptoms:

  • Asymptomatic in the majority of cases
  • Fatigue, low energy
  • In severe cases: bone pain and tenderness, muscle weakness, fracture, difficulty walking

Common Treatments:

  • Oral Vitamin D supplementation
  • Dietary optimization: fortified dairy or plant milks, fatty fish, eggs.
  • Sun exposure guidance when appropriate (balanced with skin cancer risk).
  • Calcium optimization through diet or supplements if needed.
  • Ongoing monitoring and maintenance therapy for high-risk patients.

Physical Findings:

  • Often normal.
  • Proximal muscle weakness in severe deficiency.
  • Bone tenderness (advanced cases).
  • Gait instability in older adults.

Potential Complications and Contraindications:

  • Complications of untreated deficiency:
    • Osteoporosis and fractures
    • Falls and mobility decline
    • Hypocalcemia
    • Hypophosphatemia
    • Secondary hyperparathyroidism
    • Osteomalacia (adults)
  • Contraindications / cautions:
    • Excessive supplementation can cause hypercalcemia, hypercalciuria, and Vitamin D toxicity
    • Monitor closely in chronic kidney disease.

General Health and Lifestyle Guidance:

  • Encourage consistent supplementation, as prescribed by healthcare provider, rather than intermittent missed doses.
  • Take vitamin D with a meal containing fat to improve absorption, if recommended by healthcare provider.
  • Promote weight-bearing exercise for bone health, as tolerated and approved by healthcare provider.
  • Ensure adequate calcium intake through diet or supplements (ask healthcare provider for specific recommendations).
  • Educate on realistic sun exposure and seasonal variation.
  • Reinforce follow-up labs, as directed by healthcare provider.

Suggested Questions to Ask Patients:

  • Have you been told you have low vitamin D in the past?
  • Are you currently taking a vitamin D supplement? At what dose?
  • Do you have a history of fractures, osteoporosis, or frequent falls?
  • How much time do you spend outdoors in sunlight?
  • Do you have digestive conditions or prior bariatric surgery?
  • Are you taking steroids, seizure medications, or other long-term medications?
  • Have you noticed muscle weakness, bone pain, or fatigue?

Suggested Talking Points:

  • Vitamin D is essential for bone strength, muscle function, and fall prevention.
  • Low vitamin D is common and usually easy to treat with supplements.
  • Taking your supplement consistently is the key to improving levels.
  • Your healthcare provider may recheck your blood level after treatment to ensure it’s working.
  • Proper vitamin D levels help reduce fracture risk and support overall health.

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