October 20, 2010

expert reaction to research linking time of pregnancy to childhood allergies (to be published in a BMJ Specialist Journal)

The study suggested that babies born at certain times of year could be at more risk of developing allergies.

Dr Elaine Vickers, Research Relations Manager at Asthma UK, said:

“Several studies have shown that a child’s risk of allergies seems to be influenced by their season of birth. Although this paper adds to our knowledge in this area, it’s still unclear as to why this is the case. Research like this is gradually increasing our understanding of how a child’s immune system develops in the womb and during their first years of life. As this understanding grows, so does the possibility of developing new treatments or other interventions that can alter the balance of a child’s immune system and reduce their allergy risk.”

Background from Asthma UK Other researchers have also found that children born in autumn/winter have a higher risk of food allergy than those born in spring/summer (eg Aalberse et al. 1992 & Nilsson et al. 1997) but not all believe that exposure to pollen is the cause. For example, Vassalo et al, 2010, postulated that the difference is due to the child’s exposure sunlight. This paper doesn’t add substantially to what we already know on the topic. However, the authors of this study do propose a slightly different mechanism than other scientists as they focus on the pregnant mother’s exposure to pollen rather than the baby or young child’s. References Aalberse et al 1992 – http://www.ncbi.nlm.nih.gov/pubmed/1468027 Nilsson et al 1997 – http://www.ncbi.nlm.nih.gov/pubmed/9166028 Vassalo et al, 2010 – http://www.ncbi.nlm.nih.gov/pubmed/20408340

Prof John Warner, Professor of Paediatrics and Head of Department, Imperial College London, said:

“Observational studies can be very misleading. Cardiovascular disease is more common in areas of the UK with soft tap water compared with hard water – the latter being found in the south of England. However, soft water is not the cause. It is a chance association with a whole tranche of variations in life-style between north and south being more likely explanations.

“It is improbable in the extreme that pollen exposure in the first trimester of pregnancy is the cause of higher food allergy in those born in the autumn. Contrary to the comments in the paper, the foetus at 11-12 weeks gestation is not capable of mounting an immune response to extrinsic factors. This capacity is only achieved in the middle of the 2nd trimester. There have been numerous month of birth studies in relation to allergy published over the last 30 years. Indeed I published one showing that house dust mite allergy was more common in those born in the autumn and early winter. This could relate to post-natal exposure to the house mite which is most prevalent in the autumn. However, given that any allergy is more common in relation to the same months of birth, there are equally likely to be post-natal factors such as a higher infection rate and low Vitamin D levels having an effect.

“This is an area which I have been investigating over the last 25 years and the one credible way of considering pollen exposure as having an effect would be if the mothers were pollen allergic. Under such circumstances the mother’s immune response to the pollen could impact on the foetus’ developing immune system, biasing it to a later allergy oriented response.”

Dr George Du Toit, Consultant in Paediatric Allergy, Evelina Children’s Hospital, St Thomas’ Hospital and Honorary Senior Lecturer, Kings College London, said:

“Although interesting, and in keeping with other study findings in this field, the findings are not of a significance that would warrant changes in families that wish to minimise allergy outcomes in their offspring.

“Previous studies have demonstrated that children born in autumn or winter have a higher occurrence of atopic dermatitis and bronchial asthma and higher concentrations of food-specific immunoglobulin E antibodies than children born in spring or summer. The reasons for this are not known but it there may be some seasonally varying environmental factors e.g. maternal pollen exposure that may influence allergy outcomes in the newborn. The intrauterine time period of the 11th week of gestation onwards may be a particularly important immunological period as this is when the foetus begins to produce immunoglobulin E antibodies.

“While seasonal environmental factors could interfere with this process, the timing of the development of sensitisation, a prerequisite for clinical immunoglobulin E-mediated allergic disease, has remained a controversial issue.

“This epidemiological study adds to this argument the finding that the occurrence of food allergies and food hypersensitivities may also be influenced by the season of birth and corresponding seasons during important intrauterine life. To further this argument the study compares the seasonal variation in food allergy outcomes with concentrations of pollen grains in the environment and with the relevant climatological data for the study area concerned.”

Season of the first trimester of pregnancy predicts sensitisation to food allergens in childhood: a population-based cohort study from Finland, Pyrhonen et al., published in Journal of Epidemiology and Community Health (a BMJ Specialist Journal) on Wednesday 20th October 2010.