Vitamin D

Actions

• Increases intestinal calcium absorption

• Enhances bone resorption to maintain serum calcium

• Promotes renal calcium reabsorption

Vitamin D Deficiency

Serum Levels

• Mild Deficiency: 30–49 nmol/L

• Moderate: 13–29 nmol/L

• Severe: <13 nmol/L

Causes

• Low Intake or Production

  • Dark skin (Fitzpatrick types V/VI), limited sun exposure, cultural clothing, institutionalised living

• Malabsorption: Coeliac disease, IBD, cystic fibrosis

• Impaired Metabolism: CKD, CLD, hyperparathyroidism

• Medications: Antiepileptics (e.g. phenytoin), bisphosphonates, long-term corticosteroids

• Pregnancy: Higher risk in obesity, dark skin, minimal sun exposure

Testing for Vitamin D

Indications

• Suspected osteomalacia or rickets

• Osteoporosis/osteopaenia on imaging

• Malabsorption syndromes (e.g. coeliac) or impaired metabolism (CKD)

• Long-term use of medications affecting vitamin D (e.g., corticosteroids, phenytoin)

Actions to Avoid

• No routine testing in healthy, asymptomatic individuals

• Avoid repeat testing if previous results showed sufficiency

If a Patient Requests Testing

• Explain testing is not needed without symptoms or risk factors

• Emphasise safe sun exposure and balanced diet

• Offer testing only if documented risk factors or symptoms are present

Indications for Supplementation

• If vitamin D <50 nmol/L and starting bisphosphonates

• Moderate-to-severe deficiency (<30 nmol/L)

• Clinical evidence of osteomalacia or rickets

Supplementation Guidelines

1. Mild Deficiency (30–49 nmol/L)

   • Cholecalciferol 25–50 micrograms (1000–2000 IU) daily

   • Mild cases without significant risk factors can consider increased sun exposure alone

2. Moderate-to-Severe Deficiency (<30 nmol/L)

   • Cholecalciferol 75–125 micrograms (3000–5000 IU) daily

Notes

• Sun Exposure: 5–15 minutes to face/arms mid-morning or mid-afternoon most days (longer for darker skin).

• Testing and treatment aim to prevent overtreatment in low-risk, asymptomatic people.