Objective To examine the association of circulating levels of 25-hydroxyvitamin D (25(OH)D) and ionised calcium with lung function and sensitisation to common environmental allergens in adolescents (12–19 years) and adults (20–59 years).

Design Cross-sectional study.

Participants Participants of the US third National Health and Nutrition Examination Survey (NHANES III), a representative sample of the non-institutionalised US population, with data on serum 25(OH)D levels and spirometry (adolescents, n=2074; adults, n=4647) and 25(OH)D levels and skin prick tests (adolescents, n=1914; adults, n=4782).

Main Outcome Measure Forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) from Spirometry. Skin prick test responses to a standardised allergen panel comprising indoor allergens (house mite; Dermatophagoides farinae, cat, German cockroach), outdoor allergens (short ragweed, perennial rye, Alternaria alternata, Bermuda grass, Russian thistle and white oak), and a food allergen (peanut) and a negative control. Positive allergen response was defined as maximal weal diameter ≥3 mm for allergen and <3 mm for negative control.

Results Serum levels of 25(OH)D were positively associated with FVC in adolescents (0.073 (0.025–0.121) SD) and adults (0.045 (0.013–0.078) SD) and with FEV₁ in adults (0.050 (0.013–0.087)) after adjusting for health status, previously diagnosed respiratory/allergic diseases, supplement use, household pets and demographic and socioeconomic characteristics. These associations were independent of circulating calcium levels. Calcium levels were not associated with lung function in either age group. In adults, modest positive associations of ionised calcium with sensitisation to allergens of grass origin were observed (OR per SD, 1.12(1.00–1.26) for white oak and 1.13(1.01–1.26) for Bermuda grass in fully adjusted model). These associations were independent of 25(OH)D levels. All associations remained after further adjustment for smoking and alcohol use.

Conclusion We found a cross-sectional association between serum 25(OH)D levels and lung function, which does not appear to be driven by increased allergen sensitisation. By contrast we report a novel positive association between serum levels of ionised calcium and grass allergen sensitisation in adults, which is independent of vitamin D.