Salmon in Pregnancy Study

Overview

The number of infants and children with allergic disease (dermatitis, allergies, asthma) has increased over the last several decades. This may be related to changes in diet. It is now thought that children become sensitised to allergens very early in life maybe even before they are born. Some studies show that a high omega-3 fat intake by mothers decreases risk of sensitisation in their babies. There is a biological mechanism to explain this. Omega-3 fats are found in oily fish like salmon. In the UK pregnant women are recommended to eat oily fish twice per week. However, consumption of oily fish is known to be low in pregnant women in the UK. This study sets out to identify the effects of increasing salmon intake in pregnant women. The hypothesis being investigated is that : increased consumption of oily fish during pregnancy by women at risk of having offspring who will develop atopy will increase their omega-3 fat and antioxidant status and that of their developing baby and will ameliorate the development of atopic markers and manifestations in the infants.

The prevalence of childhood atopic diseases (eczema, rhinitis \[hay-fever\], asthma, allergies) has increased dramatically over the last 30 years or so. This must be due to environmental changes. Dietary change is believed to be an important causative factor and three diet related hypotheses have been proposed. The first of these ("the PUFA hypothesis") is that the increase in intake of n-6 polyunsaturated fatty acids (PUFA) over the last 30 years has resulted in an absolute and relative decline in intake of n-3 PUFA, especially long chain n-3 PUFA. There is a plausible biological mechanism whereby a high n-6 to n-3 PUFA ratio would skew the immune system to favour sensitisation to allergens. The second diet hypothesis ("the antioxidant hypothesis") is that there is a lower status of antioxidant vitamins and minerals than 30 years ago and that the resulting increased oxidant stress skews the immune system to favour sensitisation to allergens. The third diet hypothesis ("the gut microflora hypothesis") is that the maturing microflora within the intestinal tract of the neonate plays a role in development of atopy through interactions with the gut immune system. Factors that influence development of neonatal gut microflora include maternal gut microflora and infant diet (e.g. breast milk composition). Since maternal diet will affect maternal gut microflora and also breast milk composition a link is suggested between modification of the maternal diet in pregnancy and development of atopy in the infant through an effect on gut microflora. It is now recognised that sensitisation to the allergens that trigger atopic disease occurs early in life, and in many cases in utero \[4\]. Thus, it is most likely maternal diet during pregnancy that is important in influencing risk of atopic disease in children. There is much evidence that n-3 PUFA status is lower in plasma, erythrocytes, white cells and milk of mothers of atopic children and also in umbilical cord plasma and erythrocytes \[5\]. Likewise, the status of some antioxidant minerals (e.g. Se) in cord blood has been reported to be lower in children who went on to develop atopic disease than in those who did not. Finally, atopic infants have a different gut microflora than non-atopic infants. These studies suggest that maternal status of n-3 PUFA and antioxidants, and possible of certain gut microbes, is important in determining atopic outcome in children. Not surprisingly therefore, there is substantial interest in supplementation studies in pregnant women, particularly those whose babies are at risk of atopic disease (e.g. from a family history). Fish, especially oily fish like salmon, and fish oil are very good sources of long chain n-3 PUFA. A recent study investigating the effect of fish oil supplementation in pregnant women reported an alteration in the cytokine profile of umbilical cord plasma that is consistent with protection towards atopy. The study went on to demonstrate a reduced severity of atopic dermatitis and a decreased likelihood of skin-prick positivity to a variety of common allergens in the children at one year of age. Oily fish represent a unique opportunity to reduce atopy risk because they are rich sources of both n-3 PUFA and antioxidant minerals (Se). They represent a more attractive option than supplementation with fish oil capsules. Pregnant women have a low intake of fish. Current UK recommendations are that "women of reproductive age should aim to consume within the range of one to two portions of oily fish a week". The upper limit of this range is below that for the recommendations made for boys, men and women not of reproductive age. This is because of concern about contaminants in some species of oily fish (e.g. tuna). Aquaculture producing salmon with low contaminant levels is therefore an ideal solution to enable oily fish consumption by pregnant women. Consumption of tailor-made salmon by pregnant women could prevent the development of atopic disease in their children. It is important that this be assessed through a well-designed and rigorous intervention study relating maternal oily fish consumption to atopic disease in the offspring, at the same time assessing effects of maternal fish consumption on fetal growth and maternal and fetal body composition. Hypothesis: Increased consumption of oily fish during pregnancy by women at risk of having offspring who will develop atopy will increase their n-3 PUFA and antioxidant status and that of their developing baby and will ameliorate the development of atopic markers and manifestations in the infants. Objectives: 1. To conduct a dietary intervention study in pregnant women using long chain n-3 PUFA-rich salmon. 2. To determine the effects of increased consumption of oily fish during pregnancy on fetal growth and adaptations and on maternal and fetal body composition. 3. To determine the effects of increased consumption of oily fish during pregnancy on maternal and fetal (i.e. cord blood) nutrient status 4. To determine the effects of increased consumption of oily fish during pregnancy on maternal and fetal (i.e. cord blood) immune status 5. To determine the effects of increased consumption of oily fish during pregnancy on predictors of atopic disease in cord blood, and on the development of atopic disease in infancy.