A rapid increase in atopic disorders, genetic developments of allergies such as asthma, started between 1960 and 1970 with progressive rises during the 1980s and 1990s [1]. The reunification of Germany proved the influence of lifestyle on atopic disease in a more homogeneous population between East and West Germany. Researchers showed hay fever and atopic sensitivity among children in the former East Germany both significantly increased between 1991 and 1996, which raised concerns of the ‘Western living’ influence on children, since there were lower rates of allergies in East Germany compared with West Germany [1]. In this post, I will describe the environmental influence on children from a young age as well as potential benefits children might gain from early exposure building immunity in the long-term.
- Family size and structure and atopy: The environment and size of the family in which a child grows up are shown to have an effect on allergies that children may have as well as what they are susceptible to. In the home, having siblings, sharing a bedroom as a child, and attending daycare are all shown to have decreased the probability of developing atopy due to the wide array of microbes that the child is exposed to from a young age.
- Farm and other rural exposure. Other studies have isolated farm life as a protective effect against atopy. Farm children were shown to have less atopic disease and lower levels of seroprevalence to many allergens. Environmental factors that would build this immunity include close contact with animals as a child, exposure to stables under the age of 1 year, and consumption of farm milk (presumably raw/ unpasteurized) which would build bacterial endotoxin resistance [1].
- Bacterial and viral infections: Early exposure to microbes through food-borne routes protect against respiratory allergy and that “hygiene and a westernized, semi-sterile diet may facilitate atopy by influencing the overall pattern of commensals and pathogens that stimulate the gut-associated lymphoid tissue” [1]. General exposure to infections early in life is extremely important for immune system development.
- Gut flora: Early exposure to intestinal microflora, like living on a farm, program the gut early against endotoxins. Probiotic research has been seen as beneficial in priming or maintain normal gut flora which may be beneficial to immune-related conditions, including the response to infection.
- Sanitation, water treatment: Chlorinating water has been happening for over a century now in the US and the UK. It is unlikely this can be attributed to a decreased exposure to microbes over the last 30 years. What has contributed to a decrease in microbes change in food and water quality which reduces our exposure to pathogens? This has likely altered our exposure to commensal strains, environmental strains, and pathogens. Removing pathogens in modern water treatment will remove most benign microbial bacterial contamination as well as their positive benefits.
- Immunization/vaccination: Current epidemiological studies have provided no consistent support for beneficial or adverse effects of vaccination/immunization on contracting allergies. For example, in countries with high vaccine coverage, families who choose to not vaccinate their children are unusual which increases the risk of atopy and any protective effect, depending on the population examined.
- Antibiotic therapy: It is difficult to determine the influence of antibiotic therapy on microbial exposure since there is such a close relationship between antibiotics and other atopic diseases. It is difficult to determine whether the key exposure time is related to the infection or the antibiotic. Researchers suggest the antibiotic effect could be influenced by the bacterial colonization of the gut in the early years of development.
- Breastfeeding: Breastfeeding transfers maternal antibodies which would affect the infant’s gut from a young age. By introducing this young, breastfeeding protects against intestinal pathogens and respiratory infections [1]. Some studies report the benefits of breastfeeding to include the prevention of asthma or atopic disorders later in life.
Citation:
[1] Bloomfield SF, Stanwell-Smith R, Crevel RWR, Pickup J. 2006. Too clean, or not too clean: the Hygiene Hypothesis and home hygiene. Clinical Experimental Allergy 36:402–425.
