**2. Pathogenesis of asthma**

asthma prevalence has increased in UK because of an alteration in diet associated with industrialization [1]. This has lead to a substantial decline in the consumption of fresh fruits, green vegetables, fish and red meat, and as a result decrease in pulmonary antioxidant defences and an increase in susceptibility to inhaled irritants and allergens [1]. These foods are the main sources of antioxidants, substances that protect cells against the effects of free radicals

**Genetic Factors Environmental Factors**

Smoking Allergens Occupational sensitizers Respiratory infections Parasitic infections Perinatal risk factors Diet and nutrition

Oxidative stress is important in the pathophysiology of asthma [2] and development of AHR [3]. A large number of epidemiologic studies have reported the protective effects of dietary antioxidants such as micronutrients vitamin A, C, and E, polyphenol, and carotenoids against the development of asthma and decline of lung function. In a study on American children higher levels of antioxidants beta-carotene and Vitamin C, along with antioxidant trace mineral selenium is associated with a lower risk of asthma [4]. Dietary vitamin C intake is positively associated with 1 Second Forced Expiratory Volume (FEV1) in children and adults [5-8] but less frequently with asthma or wheeze in children and adults [4, 9-11]. Dietary vitamin E intake is positively associated with ventilatory function [5, 6, 12] but negatively associated with asthma and wheeze in children [13], adult-onset wheeze [11] and the likelihood of atopic sensitization in adults [14]. Fresh fruits intake is inversely associated with wheeze [15] and chronic lung disease onset [16] and is positively associated with FEV1 [17]. Total fruit and vegetable intake is inversely related to asthma prevalence [18] but not to FEV1 [19] or airway obstruction [20]. Vegetables may protect against chronic bronchitis, asthma [21], and wheeze [22]. Moreover, dietary polyphenols intake are associated with lower disease risk with beneficial clinical outcomes attributed to both the antioxidants and anti-inflammatory properties of polyphenols [23]. Polyphenols consist of a large group of natural antioxidants

extracted from plants and flavonoids comprise the most studied group.

In addition to antioxidants, intake of fats, particularly the changing composition of polyunsa‐ turated fatty acids (PUFA) in westernized diets, has been implicated in the etiology of asthma. There has been a reduced intake of saturated fat accompanied by an increase in n-6 PUFA consumption, particularly linoleic acid and arachidonic acid. In addition, there has been a decrease in consumption of n-3 PUFA such as eicosapentaenoic acid (EPA) and docosahexae‐ noic acid (DHA). Thus, it has been postulated that the increased ratio of n-6:n-3 PUFA in diets

of industrialized countries may also contributed to the increased asthma incidence.

generated during oxidative stress.

**Table 1.** Risk factors associated with asthma

Atopy Gender Genetic predisposition Race/ethnicity

278 Using Old Solutions to New Problems - Natural Drug Discovery in the 21st Century

Airway inflammation in asthma is a complex process involving the interactions between immunological mediators produced by inflammatory cells such as mast cells, eosinophils, basophils, neutrophils, dendritic cells and lymphocytes [24]. This inflammation leads to structural and architectural changes in the airways of asthmatic patients including collagen and fibronectin deposition, wall thickening, subepithelial fibrosis and hypertrophy, goblet and airway smooth muscle cell hyperplasia, and angiogenesis, all of which collectively contribute to the phenomenon known as airway remodeling [25].

Allergic inflammation is often classified into four phases [26]:

