Nutritional factors and allergic disease : from infancy to adolescence

Abstract: Allergic disease is one of the most common non-communicable diseases in childhood. Both overweight and diet have been hypothesized to influence the risk of allergic disease. The aim of this thesis was to investigate the associations between overweight, fish intake and polyunsaturated fatty acids (PUFAs) and allergic disease throughout childhood. All analyses were performed on data from the Swedish prospective birth cohort BAMSE. The association between body mass index (BMI) status (as a measure of overweight) and risk of asthma at age 8 years was explored among 2,075 children (study I). High BMI at ages 1, 1.5, 4 and 7 years were associated with an increased risk of asthma at age 8 years. However, children with high BMI during early childhood but whose BMI normalized before age 7 years had no increased risk of asthma. In contrast, children with a high BMI at age 7 years had an increased risk of asthma, regardless of their earlier BMI. Moreover, a high BMI at age 7 years was associated with an increased risk of aeroallergen sensitization at age 8 years. Fish intake in relation to subsequent allergic disease was investigated in studies II and III. A regular fish intake (≥2-3 times/month) at age 1 year reduced the risk of allergic disease up to age 12 years in analyses of 3,285 children (study II). Restriction of the analyses to children without early symptoms of allergic disease weakened the inverse associations with asthma and eczema, but the association with rhinitis was unaffected. Regular fish consumption at school age was assessed in relation to the development of IgE- associated and non-IgE-associated rhinitis between ages 8 and 16 years in analyses of 1,590 children (study III). For total fish intake, cod or fish fingers no significant associations were observed. In contrast, a regular intake of oily fish (≥1 time/week) was associated with a reduced risk of developing rhinitis between ages 8 and 16 years, also after adjustment for infant fish intake and early symptoms of allergic disease. The association between PUFAs at age 8 years and risk of allergic disease was investigated in studies III and IV. Calculated intake of total PUFA, α-linolenic acid (18:3 n-3), total n-6 fatty acids, linoleic acid (18:2 n-6), and arachidonic acid (AA, 20:4 n-6) was not associated with rhinitis in study III. Meanwhile, higher intake of total very long-chain n-3 fatty acids (VLC n-3 fatty acids, the sum of eicosapentaeonic acid [20:5 n-3], docosapentaeonic acid [22:5 n-3], and docosahexaeonic acid [22:6 n-3]), was associated with a reduced risk of developing non-IgE-associated rhinitis between ages 8 and 16 years. The composition of PUFAs was measured in plasma phospholipids for a subsample of 940 children. Increasing proportion of total VLC n-3 fatty acids was associated with a reduced risk of asthma, rhinitis and aeroallergen sensitization at age 16 years in study IV. In addition, total VLC n-3 fatty acids was associated with a reduced risk of developing asthma between ages 8 and 16 years. AA was associated with a reduced risk of asthma and aeroallergen sensitization at age 16 years. The inverse associations between total VLC n-3 fatty acids and AA and allergic disease were most pronounced for the IgE-associated phenotypes. In conclusion, the results in this thesis imply that modifiable factors influence the risk of allergic disease in childhood. Early-transient high BMI does not seem to increase the risk, while persistent and late high BMI seem to be associated with concurrent asthma and aeroallergen sensitization at school age. Moreover, fish intake, both in infancy and childhood, and PUFAs, especially VLC n-3 fatty acids, were associated with a reduced risk of subsequent allergic disease throughout childhood.