Sunlight & Vitamin D

❍ At a glance

• Vitamin D deficiency (25-OH vitamin D below 50 nmol/L) is common in New Zealand despite the country's reputation for sunshine. UV levels at southern NZ latitudes are insufficient for meaningful cutaneous synthesis between May and August. Year-round deficiency is especially prevalent in people who are housebound, institutionalised, or have darker skin pigmentation.
• Testing is funded only with clinical justification - not indiscriminate. Funded indications: documented risk factors for deficiency, symptoms consistent with deficiency (fatigue, bone pain, proximal myopathy), prior fragility fracture or osteoporosis management, or monitoring of established supplementation.
• Target serum 25-OH vitamin D for bone health: at least 50 nmol/L. Supplementation: cholecalciferol (vitamin D3) 1,000-2,000 IU daily for maintenance; loading doses (50,000 IU weekly for 6-8 weeks) for severe deficiency before switching to maintenance.
• New Zealand has one of the highest melanoma rates in the world. The clinical message is not "maximise sun exposure" - it is balance: enough UV for synthesis, adequate photoprotection to reduce cancer risk.

❍ Who to test, targets, and supplementation

Testing is appropriate - but not indiscriminate. Routine 25-OH vitamin D testing in asymptomatic low-risk individuals is not recommended and is not funded under the community schedule in New Zealand without clinical justification. Funded indications include: documented risk factors for deficiency (institutionalisation, malabsorption, limited sun exposure, pigmented skin in at-risk climates), symptoms consistent with deficiency (fatigue, bone pain, proximal myopathy), prior fragility fracture or osteoporosis management, and monitoring of established supplementation.

Target serum 25-OH vitamin D for bone health: at least 50 nmol/L; levels below 25 nmol/L represent severe deficiency. For musculoskeletal and immune function, some guidelines suggest a target of at least 75 nmol/L in high-risk groups, though the evidence for benefits beyond bone health at these higher levels is less robust.²

Supplementation with cholecalciferol (vitamin D3) is the standard approach; ergocalciferol (vitamin D2) is less well absorbed. A dose of 1,000-2,000 IU daily is appropriate for maintenance in deficient adults. Loading doses (e.g. 50,000 IU weekly for 6-8 weeks) may be used for severe deficiency before switching to maintenance dosing. Dietary sources of vitamin D are limited - oily fish, egg yolks, and some fortified foods contribute, but dietary intake alone is rarely sufficient to maintain adequate levels in deficient individuals.

The competing risk is melanoma. New Zealand has one of the highest melanoma rates in the world - a consequence of latitude, ozone depletion history, outdoor culture, and fair-skinned European ancestry in a high-UV environment.³ The clinical message is not "maximise sun exposure" but rather: balance. In practice, approximately 10-15 minutes of midday sun exposure to the arms and legs on most summer days for fair-skinned adults, with sun protection applied after that. In winter in the South Island, meaningful synthesis is unlikely regardless of exposure duration - supplementation is more practical than sun exposure in that context.

❍ Toxicity and special populations

Vitamin D toxicity (hypercalcaemia) from supplementation is rare but documented with very high doses, typically above 10,000 IU/day for prolonged periods. Routine monitoring of 25-OH vitamin D levels during supplementation is not necessary at standard doses unless there is a clinical reason to suspect toxicity or malabsorption.

The exception is patients with granulomatous disease (sarcoidosi