Exposure to ‘farming’ and objective markers of atopy: a systematic review and meta‐analysis

Abstract

There is growing interest in the 'farm effect' on the spectrum of allergy. Evidence concerning the farm effect on asthma, eczema, and allergic rhinitis has been systematically synthesized, but without a specific focus on objective markers of sensitization. This focus is important, as farm exposures may be related to allergy but not to non-allergic phenotypes of disease. We aimed to systematically review and meta-analyse literature that has investigated associations between farm exposure at any age and objective measures of atopy, that is serum IgE or skin prick tests results. Using predefined inclusion and exclusion criteria, we identified 29 articles for review. IgE levels were measured in either childhood or adulthood by eighteen studies, while skin prick testing was performed in sixteen studies. Newcastle-Ottawa Scale quality assessments indicated that the majority of these studies demonstrated a representative sample of selected participants. Due to significant heterogeneity in study measures and methodology between studies, only few were meta-analysed. This meta-analysis showed a significant protective effect of farm exposure before 1 year of life on allergic sensitization (OR = 0.60 [0.52-0.70]). Farm exposure during childhood was also associated with a reduced risk of sensitization to cat or timothy (OR = 0.60 [0.51-0.70]; OR=0.46 [0.41-0.51]). Studies investigating the effect of farm exposure in adult life could not be meta-analysed, and their results were inconsistent. Insufficient studies investigated food sensitization as an outcome to allow synthesis. The majority of studies included in this review investigated childhood farm exposure, finding evidence to support a protective childhood 'farm effect' against subsequent atopy. There is inconsistent evidence on the association between farm exposure in adulthood and allergic sensitization. Further studies are needed to tease out the exact exposures and timing associated with farming environments that protect against allergic disease.

High exposure to endotoxin in farming is associated with less new-onset pollen sensitisation

“…In contrast, new HDM sensitisation was apparently not influenced by farm work exposures (figure 2, table 2), and loss of HDM sensitisation seemed even less likely at higher farm-related exposures. These findings are in fact in line with those of various other studies in both children and adults, as summarised in a recent systematic review and meta-analysis by Campbell et al 30 of studies with IgE serological data from farm children, farmers and respective control groups.…”

The effects of growing up on a farm on adult lung function and allergic phenotypes: an international population-based study

“…To date, the majority of work done on farm exposures has focused on the association between early-life farm contact and childhood allergic and respiratory disease outcomes, while very few studies have investigated the impact of early-farm contact on adult disease, and especially adult lung function 9. Our findings on the impact of farm exposure on lung function in women are novel.…”

“…Systematic reviews synthesising considerable evidence from studies on early-life farm exposure and childhood disease outcomes have shown a decreased risk of asthma, wheeze and allergic disease associated with the ‘farm effect’ 3 9. However, fewer studies have analysed the impact of these childhood exposures on well-defined allergic adulthood outcomes or the potential persistence of the ‘farm effect’ into adult life 2 3 9. While the majority of existing research has investigated allergic outcomes including asthma, little work has been conducted on the association between early-life farm exposure and clinical measures of lung function in childhood, adolescence or adulthood 10–14.…”

Do farm-grown lungs breathe better?

“…Recent systematic reviews with meta-analyses show a strong protective effect of growing up on a farm on childhood atopy2 and a lesser effect on childhood asthma 3. In these meta-analyses, the effect estimates for the ‘farm-effect’ on asthma were much more heterogeneous than those on any atopic sensitisation 2 3.…”