Effect of daily sunscreen application on vitamin D: findings from the open-label randomized controlled Sun-D Trial.

Summary

In a population-based, open-label RCT (n=628 analyzed; Australia), routine use of SPF50+ sunscreen for ~1 year lowered serum 25(OH)D by 5.2 nmol/L versus discretionary use and increased vitamin D deficiency prevalence (45.7% vs 36.9%; PR 1.33). Effects were consistent across subgroups; the trial was registered and analyses were blinded to allocation.

Key Findings

• Routine SPF50+ use for ~1 year reduced serum 25(OH)D versus discretionary use (between-group effect −5.2 nmol/L, 95% CI −7.2 to −3.2).
• Vitamin D deficiency at study end was more prevalent with routine sunscreen (45.7%) than control (36.9%) (prevalence ratio 1.33, 95% CI 1.14–1.55).
• Effects were broadly consistent across baseline vitamin D status, UVR zones, and personal exposure strata; trial registered (ACTRN12621001752853).

Clinical Implications

Counsel regular sunscreen users about potential vitamin D insufficiency; consider periodic 25(OH)D testing and supplementation, especially in low-UV seasons or at-risk individuals.

Limitations

• Open-label design may introduce behavior changes and measurement bias.
• Findings from Australia may not generalize to regions with different UV climates or sunscreen use patterns.

Future Directions

Define vitamin D testing/supplementation algorithms for regular sunscreen users; evaluate impacts of different SPF levels, application frequencies, and formulations across latitudes.