Collectively , the evidence suggests that higher serum levels of 25(OH)D are associated with a reduced risk of asthma exacerbations , but there was little evidence to suggest an association with asthma incidence , prevalence or severity .
Asthma is a major public health issue .
The co-occurrence of the high prevalence of asthma and vitamin D deficiency documented globally in recent decades has prompted several investigations into a possible association between the two conditions .
The objective of this paper was to synthesize the evidence from studies that have measured the association between serum vitamin D  and asthma incidence , prevalence , severity and exacerbations .
Serum micronutrient concentrations and childhood asthma: the PIAMA birth cohort study.
BACKGROUND Research suggests an influence of micronutrients on  childhood asthma .  So far , evidence mainly originates from cross-sectional studies using nutrient intake data , which is not an accurate measure of nutrient status . This study aim ed to investigate the cross-sectional and prospect i ve associations between serum concentrations of magnesium , vitamin D , selenium , and zinc and prevalence of ( severe ) asthma , atopy , and bronchial hyperresponsiveness ( BHR ) in childhood . METHODS In the Prevention and Incidence of Asthma and Mite Allergy birth cohort study , serum nutrient concentrations were available for a 4-yr-old subgroup ( n = 372 ) and for a different 8-yr-old subgroup ( n = 328 ) . Yearly question naires inquired about asthma prevalence until 8 yr of age . Allergic sensitization was measured at 4 and 8 yr of age ; BHR was measured at 8 yr of age . Data were analyzed with logistic regression and generalized estimating equations models . RESULTS There was a consistent ( non-significant ) inverse association between serum magnesium concentrations and asthma prevalence . Serum vitamin D concentrations measured at age 4 were inversely associated with asthma at ages 4 - 8 [ e.g. , cross-sectional association between vitamin D tertile 3 vs. 1 and severe asthma : odds ratio ( OR ) : 0.49 , 95 % confidence interval ( CI ) : 0.25 - 0.95 ] , whereas vitamin D measured at age 8 was positively associated with asthma at age 8 ( e.g. , cross-sectional association between vitamin D tertile 3 vs. 1 and severe asthma : OR : 2.14 , 95 % CI : 0.67 - 6.82 ) . CONCLUSIONS Our study contributes to the evidence that children with higher serum magnesium concentrations are less likely to have asthma . The associations between serum vitamin D concentrations and asthma were age-dependent
Collectively , the evidence suggests that higher serum levels of 25(OH)D are associated with a reduced risk of asthma exacerbations , but there was little evidence to suggest an association with asthma incidence , prevalence or severity .
Asthma is a major public health issue .
The co-occurrence of the high prevalence of asthma and vitamin D deficiency documented globally in recent decades has prompted several investigations into a possible association between the two conditions .
The objective of this paper was to synthesize the evidence from studies that have measured the association between serum vitamin D  and asthma incidence , prevalence , severity and exacerbations .