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- Materials and methods
Background Dietary fatty acid intake has been proposed to contribute to asthma development with n-6 polyunsaturated fatty acids (PUFA) having a detrimental and n-3 PUFA a protective effect.
Objective The aim of our analysis was to explore the relationship between fatty acid composition of serum cholesteryl esters as marker of dietary intake and prevalence of asthma, impaired lung function and bronchial hyper-responsiveness in children.
Methods The study population consisted of 242 girls and 284 boys aged 8–11 years, living in Munich, Germany. Data were collected by parental questionnaire, lung function measurement and skin prick test according to the International Study of Asthma and Allergies in Childhood phase II protocol. Confounder-adjusted odds ratios (OR) with 95% confidence intervals (CI) were calculated for the association between quartiles of fatty acid concentration and health outcomes with the first quartile as reference.
Results n-3 PUFA: levels of eicosapentaenoic acid were not related to asthma and impaired lung function. Linolenic acid levels were positively associated with current asthma (OR for fourth quartile 3.35, 95% CI 1.29–8.66). Forced expiratory volume in 1 s (FEV1) values decreased with increasing levels of linolenic acid (p for trend=0.057). n-6 PUFA: there was a strong positive association between arachidonic acid levels and current asthma (OR4th quartile 4.54, 1.77–11.62) and a negative association with FEV1 (P=0.036). In contrast, linoleic acid was negatively related to current asthma (OR4th quartile 0.34, 0.14–0.87) and FEV1 values increased with increasing levels of linoleic acid (P=0.022). The ratio of measured n-6 to n-3 PUFA as well as levels of palmitic and oleic acid were not consistently related to asthma or lung function.
Conclusion Our data do not support the hypothesis of a protective role of n-3 PUFA. Elevated arachidonic acid levels in children with asthma may be because of a disturbed balance in the metabolism of n-6 PUFA or may be secondary to inflammation in these patients.
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- Materials and methods
Changes in diet, especially in its fatty acid composition, have been hypothesized to contribute to the worldwide increase in asthma [1–3]. Typical Western diets are characterized by an imbalance of n-6 to n-3 polyunsaturated fatty acids (PUFA): the ratio has risen considerably from between 1:1 to 2 : 1 in former times to a ratio of 20:1 to 30:1 recently .
n-6 and n-3 PUFA are both precursors of eicosanoids as inflammatory mediators. Whereas linoleic acid (18:2 n-6) can be converted to arachidonic acid (20:4 n-6), a precursor of the highly pro-inflammatory two-series prostaglandins and four-series leukotrienes, α-linolenic acid (18:3 n-3) is metabolized to eicosapentaenoic acid (20:5 n-3), a precursor of the less inflammatory three-series prostaglandins and five-series leukotrienes, and which competitively inhibits the metabolism of arachidonic acid. Eicosanoids derived from arachidonic acid are important mediators of allergic inflammation. Moreover, prostaglandin E2 inhibits the production of T-helper type 1 (Th1)-type cytokines without interfering with Th2-type cytokines, and stimulates IgE-production by B lymphocytes .
Several studies investigating the impact of fat consumption or fish oil supplementation in children supported the fatty acid hypothesis. A high dietary intake of polyunsaturated fats, mainly n-6 PUFA, has been shown to be associated with an increased risk of wheeze or asthma [6–8]. On the other hand, consumption of fish or fish oil as main source of n-3 PUFA seemed to decrease asthma risk [9, 10].
Fatty acid levels in the blood are biochemical markers of dietary intake and may be used in observational studies to investigate relative patterns of fat intake [11, 12]. The composition of fatty acids in serum cholesteryl esters is insensitive to daily variation in diet and reflects the composition of dietary fat consumed in preceding weeks . Compared with the other lipid fractions of serum, cholesteryl esters have the advantage of a greater stability of its fatty acid composition during storage and are therefore best suited for epidemiological studies .
Only a few studies analysed the fatty acid composition of cholesteryl esters in relation to asthma in children and these gave conflicting results. Leichsenring et al.  compared 17 asthmatic children with 10 healthy controls and observed higher levels of linoleic acid and lower levels of arachidonic acid in plasma cholesteryl esters of the asthmatics. In contrast, Dunder et al.  found no differences in serum cholesteryl ester fatty acids between 47 asthmatic children and 47 controls.
The objective of our study was to investigate the association between fatty acid composition of serum cholesteryl esters and prevalence of asthma symptoms, physician-diagnosed asthma, impaired lung function as well as bronchial hyper-responsiveness in a population-based sample of children.