Vitamin D is a secosteroid with a pivotal role in the calcium and phosphate metabolism, two ions that are essential for bone mineralization, neuromuscular activity and general cell functions. Sources of vitamin D are either endogenous (production in the skin from 7-dehydrocholesterol under the influence of sunlight UV-B radiation) [1] or exogenous (dietary). The dietary forms of vitamin D are either of vegetal origin (ergocalciferol, vitamin D2) [2] or of animal origin (colecalciferol, vitamin D3) [3]. The two calciferol forms are similarly metabolized in humans, have equal bioavailability and effectiveness [4]. [...]

Asthma is a heterogeneous group of disease entities with common characteristics such as intermittent respiratory symptoms (wheezing, tightness, cough, dyspnea), reversible airway obstruction and bronchial hyperresponsiveness [1]. Wheezing, caused by airflow restriction through narrowed airways, is the main clinical sign associated with asthma.
Two concepts related to asthma are currently in a process of disentanglement: the concept of asthma phenotypes (particular clinical characteristics, without reference to the underlying pathologic process) and endotypes (pathological mechanisms of disease) [2]. The disentangling of asthma phenotypes and endotypes is important for the prediction of disease evolution and for accurate therapeutic action.