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The list
of things or circumstances which seem to protect against asthma grows
longer monthly. To “Being small for dates” at birth has now
been added prematurity, which was associated with reduced allergic sensitisation
by age 10 from 37% to 17%[1].
Colds and
other droplet infections in childhood have been joined by infections,
often symptomless, transmitted by mouth (hepatitis A, Toxoplasma, Helicobacter)[2].
Further
supporting the ‘Hygiene Hypothesis’ (the immune system needs
stimulation by suitable micro-organisms to develop ‘normally’
without allergies), is a study from Austria, which showed less than
a third the asthma prevalence by age 8–10, in children living on
a farm, compared with those not living on a farm[3]. Similar researches
in Germany and Finland confirm this allergy protective effect of a farm
environment in childhood[4, 5]. 
In view of these studies, the earlier finding that a cat in the home
from birth is also protective, is slightly less astonishing; “Childhood
exposure to pets including cats was associated with lower sensitization
to cats in adulthood…” [6].
Advice hitherto has been to remove, as far as possible, all pets from
the house well before the birth of a baby into a family with a history
of allergies. Protection has also been shown to follow daily doses of
Lactobacillus rhamnosus, given to 159 mothers daily for 2–4 weeks
before delivery, continuing for breast-feeding mothers, or given directly
to the infants, for 6 months after the birth [7].
By 2 years of age, eczema incidence in the treated infants was only
half that in controls. Although the method sounds promising, occasional
septicaemia in immuno-deficient subjects in the past necessitates caution
and further study, before it can be recommended.
The international ISAAC study has found a reduced prevalence of allergic
disease amongst children age 13–14 who received the greatest amount
of their calories from cereal and rice, and their protein mainly from
cereals, nuts and vegetables, with minimum intake of meat and dairy
products—hardly the NZ style![8]. Whether the anti-oxidant content
of this kind of diet is the main factor responsible for the apparent
protection remains to be discovered.
References:
1
J Allergy Clin Immunol 2001;107:229-34
2 BMJ 2000;320:412-17
3 Clin Exp Allergy 2000;30:194-200
4 Ibid 187-193
5 Ibid 201-08
6 J Allergy Clin Immunol 1999;104:941-47
7 Lancet 2000;357:1057-9 & 1076-79
8 Eur Resp J 2001;17:436-43
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