27th February 2025

Vitamin D deficiency

In UK populations, >80% of vitamin D is derived from exposure to sunlight, with the remainder acquired through dietary sources. Except in uncomplicated deficiency of doubtful clinical significance, measurement of renal function, calcium, phosphate, PTH, and ALP should be considered, particularly if complications of deficiency are suspected.

Risk factors for deficiency include poor sun exposure, darker complexion, pregnancy/breastfeeding, obesity, age over 65, malabsorption disorders, and severe hepatic or renal disease. Vitamin D deficiency is also associated with a range of other conditions, including diabetes, most cancers, and auto-inflammatory diseases, though this is unlikely causative in any significant way.

Those with risk factors are advised to take a 400 IU supplement of vitamin D2 or D3 daily, with all other adults advised to take supplements only in the autumn and winter. If found to be deficient, non-urgent cases (i.e. asymptomatic, no relevant comorbidities, no drug indications) can be treated with a maintenance regimen of 800-2,000 IU daily, whereas those requiring faster correction require a loading dose of 280,000-300,000 IU over 6-10 weeks before reducing to maintenance levels.

Caution is advised when prescribing in pregnant or breastfeeding patients, while patients with a high risk of hypercalcaemia or renal stones, gastrointestinal disorders resulting in vitamin D malabsorption, or end-stage liver or kidney disease (i.e. have impaired hydroxylation of vitamin D to its active metabolite) should not receive standard supplementation.