Exposure to the outdoor natural environment
Reduced exposure to important microbial species has also occurred because of reduced contact with our outdoor environment and the huge diversity of microbial and helminth (worms) species which it contains. Urbanisation has accelerated loss of exposure to the natural environment. We now spend up to 80% of our time indoors
Studies consistently show that exposure to a farm environment in early life can protect from asthma. The diverse composition of the human microbiome depends on input from the natural environment.
Studies in Finland show that the skin microbiota from individuals living close to agricultural land was more diverse than from those living close to urban centres, and was associated with reduced atopic sensitisation.
Could antibiotics be involved?
Antibiotic usage shows a good temporal fit
- Increasing antibiotic use since 1950s
- Steep rise in allergies from 1970s
Epidemiological studies show that antibiotics may be a risk factor for allergies, particularly excessive use by pregnant mothers or young babies
- Evidence of a link for asthma, cow’s milk allergy, IBD, eczema
Antibiotics may interact with microbes in the gut leading to reduced diversity of human gut microbiome
Although there is concern about possible confounding of epidemiological studies, studies with humans and mouse models now support this concept.
They show mechanisms by which reduced microbiota diversity can be associated with development of inflammatory disease