Prevention of allergy and autoimmune disease

See also asthma prevention.

Immune function starts development in the first trimester, in the womb. The TH1 cytokine IFN gamma is constrained, probably to protect the placenta. Most innate and adaptive immune processes are fully developed by the end of the pre-school years, with the exception of airway mucosal dendritic cells which continue to expand up until puberty. The major driving force behind postnatal immune development in all mammalian species is microflora of the gastrointestinal tract, and it seems “healthy” development requires the right balance of microflora becoming established, at a crucial window in time.

The hygiene hypothesis (David Strachan) has now been modified to include “old friends” (Graham Rook, talking about microbes that have co-evolved with humans) and finally the biodiversity hypothesis.

So lifestyle becomes important – time spent outdoors, time spent in contact with natural habitats, having diverse, unprocessed diets. Fresh fruit and vegetables have their own microbiome, for instance. And these things are heavily linked to socioeconomic status, particularly housing and green space. Role of artificial sweeteners, emulsifiers, plasticisers and other waste organic compounds?

Mode of delivery affects neonatal colonisation (elective vs emergency section or vaginal) – although so far maternal-infant microbial seeding studies have failed to demonstrate health benefits.

More than 20 studies of probiotics and prevention of allergy.  No safety concerns.  15 found supplementation during pregnancy and lactation may reduce eczema, but no effect in asthma, food allergy, rhinitis.

Fish oil (omega-3) supplementation during pregnancy may reduce risk of allergic sensitisation to egg.

Cochrane 2013 review of prebiotics concluded “promising results in high risk populations”, WAO find in favour (probiotics too), but others institutions have not!

Other dietary exposures, including maternal allergenic food avoidance, vitamin, mineral, fruit and vegetable intake did not appear to influence risk of allergic or autoimmune disease.

There is limited evidence to suggest that supporting mothers to breastfeed for longer reduces risk of eczema in the first year

Longer exclusive breastfeeding duration reduces risk of type 1 diabetes.

2 previous systematic reviews suggested extensively hydrolyzed formula may be protective against milk allergy in high risk babies.  Partially hydrolysed found to possibly protect in 2 systematic reviews.  Certainly some studies with no effect.  Soya does not help!  EAACI have recommended hypoallergenic formula (“one with documented preventive effect”) for 4/12  (Grade I, evidence A-B), but Cochrane have withdrawn their 2017 review, which was also in favour, “due to data entry error”.

[PLoS Med metanalysis 2018]

Bigger issue of course is the microbiome and exposome.