24 December 2013 Last updated at 00:12 GMT
Eating nuts during pregnancy 'may curb allergies'
Children are less likely to have a nut allergy if their mother ate nuts while pregnant, a study has concluded.
The work, published in JAMA Pediatrics, looked at the health and diets of more than 8,000 children and their mothers.
The US researchers believe that early exposure in the womb creates natural tolerance to certain foods.
But the findings conflict with other studies that have shown either no effect or a possible risk from nut consumption.
Experts say this makes it difficult to offer firm advice to mothers-to-be, with the exception of women who are themselves allergic to nuts and should therefore always avoid eating them.
The study authors, led by Dr Lindsay Frazier of the Dana-Faber Children's Cancer in Boston, concluded children were a third less likely to have a nut allergy if their mothers had eating nuts during pregnancy.
This included tree nuts such as walnuts, almonds, pistachios, cashews, pecans, brazils, hazelnuts and macadamias as well as peanuts.
The authors say this suggests that nut consumption may protect against future allergies.
But there are other factors that may also explain this difference.
For example, the women who ate nuts were also more likely to have healthier diets containing plenty of fruit and vegetables.
Dr Adam Fox, consultant children's allergist at Guy's and St Thomas's NHS Foundation Trust, said the findings were interesting but inconclusive.
"To make things even more complicated, there is also strong evidence to suggest that nut allergy doesn't develop until after birth and that it is exposure of the infant's skin to nut protein that is most important in the development of allergy.
"With such differing results from different studies, it is currently impossible to offer advice about exactly what mothers should do regarding nut consumption during pregnancy but current international guidance is that there is no need to either avoid nuts, nor to actively eat them."
Prospective Study of Peripregnancy Consumption of Peanuts or Tree Nuts by Mothers and the Risk of Peanut or Tree Nut Allergy in Their Offspring
A. Lindsay Frazier, MD, ScM1,2; Carlos A. Camargo Jr, MD, DrPH2,3,4; Susan Malspeis, MS2; Walter C. Willett, MD, DrPH4,5,6; Michael C. Young, MD7
[+] Author Affiliations
JAMA Pediatr. Published online December 23, 2013. doi:10.1001/jamapediatrics.2013.4139
Importance The etiology of the increasing childhood prevalence of peanut or tree nut (P/TN) allergy is unknown.
Objective To examine the association between peripregnancy consumption of P/TN by mothers and the risk of P/TN allergy in their offspring.
Design, Setting, and Participants Prospective cohort study. The 10?907 participants in the Growing Up Today Study 2, born between January 1, 1990, and December 31, 1994, are the offspring of women who previously reported their diet during, or shortly before or after, their pregnancy with this child as part of the ongoing Nurses’ Health Study II. In 2006, the offspring reported physician-diagnosed food allergy. Mothers were asked to confirm the diagnosis and to provide available medical records and allergy test results. Two board-certified pediatricians, including a board-certified allergist/immunologist, independently reviewed each potential case and assigned a confirmation code (eg, likely food allergy) to each case. Unadjusted and multivariable logistic regression analyses were used to evaluate associations between peripregnancy consumption of P/TN by mothers and incident P/TN allergy in their offspring.
Exposure Peripregnancy consumption of P/TN.
Main Outcomes and Measures Physician-diagnosed P/TN allergy in offspring.
Results Among 8205 children, we identified 308 cases of food allergy (any food), including 140 cases of P/TN allergy. The incidence of P/TN allergy in the offspring was significantly lower among children of the 8059 nonallergic mothers who consumed more P/TN in their peripregnancy diet (?5 times vs <1 time per month: odds ratio?=?0.31; 95% CI, 0.13-0.75; Ptrend?=?.004). By contrast, a nonsignificant positive association was observed between maternal peripregnancy P/TN consumption and risk of P/TN allergy in the offspring of 146 P/TN-allergic mothers (Ptrend?=?.12). The interaction between maternal peripregnancy P/TN consumption and maternal P/TN allergy status was statistically significant (Pinteraction?=?.004).
Conclusions and Relevance Among mothers without P/TN allergy, higher peripregnancy consumption of P/TN was associated with lower risk of P/TN allergy in their offspring. Our study supports the hypothesis that early allergen exposure increases tolerance and lowers risk of childhood food allergy.
Peanut allergy affects 1% to 2% of the population in most Western countries,1- 3 and in the United States, the prevalence of childhood peanut allergy has more than tripled, from 0.4% in 1997 to 1.4% in 2010.4 Typically, the onset of peanut allergy is in early childhood; 70% of reactions occur during the first known exposure.5 These IgE-mediated hypersensitivity reactions require prior allergen exposure and sensitization, implying that prior exposure to peanut had already occurred in utero or through unknown exposures in the diet or environment, such as through skin or respiratory routes.6 Because of frequent overlap between peanut allergy and tree nut allergy and their similar natural history, with 80% to 90% persistence of the food allergy into adulthood,7 these 2 allergies are often considered together as peanut or tree nut (P/TN) allergy.
For many years, pediatric guidelines have recommended the avoidance of P/TN for at least the first 3 years of life, with some experts also recommending that P/TN be avoided during pregnancy.8 These recommendations were rescinded recently when literature reviews showed little support for them.9,10 For decades, many investigators have posited that modifications of the maternal diet during pregnancy might prevent food allergies.11- 14 However, some studies on maternal avoidance of peanut during pregnancy actually demonstrated an increase in peanut sensitization in the child,15- 17 while other studies found no association.5,14,18,19 In related research, early exposure to allergenic foods in infant diets may decrease sensitization and increase oral tolerance to those foods.20- 24
Given the lack of clarity in the current literature, an important quandary exists: should the pregnant mother include or exclude P/TN in her diet? The goal of our investigation was to clarify the association between peripregnancy consumption of P/TN by mothers and the subsequent development of P/TN allergy in their offspring.
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