wheezing" is defined as a musical sound caused by the passage of air through narrow respiratory tract airways . Recurrent wheeze is defined as three or more episodes of parentally reported wheeze in the past 12 months of Various risk factors are associated with recurrent wheezing and asthma: small airway caliber; decreased lung function at birth; viral respiratory infections; environmental pollution; pets; early daycare attendance; passive smoking; parental history of asthma or atopy; obesity; and socioeconomic factors.

There has been growing recognition of the critical extra-skeletal roles for vitamin D in recent years with an explosion of interest in vitamin D across health disciplines including lung disease. Recently, vitamin D was found to be low in patients with recurrent wheezes.

Vitamin D, whether produced in the skin upon sun exposure or ingested from various dietary sources, is converted in the liver to 25-hydroxyvitamin D [25(OH)D]. The latter is the major circulating form of vitamin D and is thus used for evaluating the vitamin D status of patients . The flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources of vitamin D and the fortified cereals and milk provide adequate amounts as well.

Studies in animal models and humans have demonstrated an association of low vitamin D concentrations with atopy and respiratory tract conditions. The mechanism that explains this association is still unclear. It has been suggested that this mechanism is due to the effects of vitamin D status on the regulation of the immune system.

The vitamin D receptor is expressed in various cells of the immune system, such as macrophages, monocytes, dendritic cells, and natural killer cells, as well as in B and T lymphocytes. Binding of the active form of vitamin D to its receptor leads to an increase in immunomodulatory activity that maintains the balance between the cellular immune response (Th1) and the humoral response (Th2), in addition to stimulating regulatory T cells.

Hypomagnesaemia (serum Mg level <0.74 mmol.L-1) has been also suggested to be associated with increased incidence of wheeze, airway hyperreactivity, and impairment of lung function. The mechanisms of action of magnesium (Mg) on respiratory airways are multiple and include relaxation of airways smooth muscle, bronchodilatation, anticholinergic effect, and stabilization of the mast cells

Inclusion Criteria:

• Any child with three or more episodes of parentally reported wheeze aged from 1 month to less than 6 years admitted at pediatric department of Sohag University Hospital.

Exclusion Criteria:

• patients with chronic lung and congenital heart diseases.
• Patients with body mass index (BMI) below 3rd percentile and those ≥ 85th percentile will be excluded to avoid effect of disturbed nutritional status on vitamin D level and occurrence of wheezing.

The study will include any child with three or more episodes of parentally reported wheeze aged from 1 month to less than 6 years admitted at pediatric department of Sohag University Hospital.