by Wei Perng, PhD
The increase in allergic diseases has also been attributed to the fact that pregnant women aren’t eating enough fish. The U.S. Environmental Protection Agency and the Food and Drug Administration issued advice for pregnant women (or those likely to become pregnant) to limit their seafood consumption to 2-3 servings per week, due to concerns regarding the detrimental effects of mercury on the fetus. However, as we discussed in a previous blog post, marine fish are also a natural source of omega-3 (N-3) and omega-6 (N-6) polyunsaturated fatty acids (PUFA), which are crucial for development of the immune system. While pregnant women may limit their fish intake to protect their child’s developing brain, they may also be consuming too few N-3 and N-6 PUFAs, which could adversely influence the immune system and contribute to the rising prevalence of allergic disease.
It may be that infants are exclusively breastfed for too long. The World Health Organization (WHO) recommends exclusive breastfeeding for at least 6 months in order to provide ideal nutrition for proper growth and development. Although this practice provides clear benefits for length and weight gain, especially in developing settings where resources are limited, delaying complementary foods until 6 months of age may actually increase risk of immune disorders. Animal models suggest that exposure to common allergens during an early critical window of development may be essential towards developing tolerance of those allergens. Further, this time frame may also coincide with the establishment of healthy gut bacteria, which is essential to promoting allergen tolerance.
The obesity epidemic. The past two decades has seen a parallel uptick in both obesity and allergic disease, hinting at a possible link between the two. Prospective population-based studies have observed a direct association between higher body mass index (BMI) and risk of asthma in children and adults. A weight loss trial conducted among obese adolescents found that lowering BMI led to improvements in lung function, suggesting a causal relationship between excess weight and risk of some allergic disorders. How might obesity lead to allergies? As summarized in a recent review, the link may depend on the specific allergic disease. In airway allergies, obesity may affect the mechanics of lung function; in allergies like eczema or hay fever, inflammation may be the cause. Obesity and allergies may also be connected by shared risk factors including poor diet, genetics, and a sedentary lifestyle.
So, is the solution to allergies to lose weight, stop washing your hands, eat lots of fish while pregnant, and introduce solid foods to your newborn as early as possible? Not quite. As with the case of sunscreen and rickets, public health victories are sometimes met with unintended consequences. Further research to identify the ideal balance between too much and too little allergen exposure will fine tune clinical recommendations.