A recent study provides certain implications for
an association between exposure to antibiotics at a young age and the
development of allergic diseases, primarily asthma, in early childhood.1
At
some point, most people have gone to the doctor’s office and left with a
prescription for an antibiotic. In today’s world, antibiotics have developed a
connotation as a medicine that can ward off all sorts of sicknesses, which is only
partially true. What many people don’t realize is that antibiotics are strictly
useful for fighting bacterial infections and will have no effect on viral illnesses.*
Although antibiotics have saved countless lives since the discovery of
penicillin, there are some concerns about their use.
There two main negative consequences of
using antibiotics more liberally than in the past: some unhealthy bacteria have
increased resistance to treatment and administration of antibiotics can lead to
decreased levels of healthy bacteria. The first consequence relates to
overprescribing antibiotics for patients that may not be suffering from a
bacterial infection. Every time a person takes antibiotics, he or she increases
the likelihood that bacteria in the body will become resistant, which makes it
difficult to treat later infections.#
 |
| Commensal Bacteria |
The second consequence, which directly
relates to the study in question, has to do with the healthy bacteria that
reside in the human gastrointestinal tract. When antibiotics are introduced to
the body during infancy, a critical period for the development of the immune
system, disruption to gut microflora can occur.1 This could possibly
predispose patients to the development of an allergic phenotype. Research shows
that disruptions in the normal growth of gastrointestinal bacteria can prevent
regulatory T cells from properly dampening the immune system’s response to
respiratory allergens.$ For
more information, click here. Reduced diversity of microbes in infant excrement
has also been connected to an increased risk of allergic diseases late in
childhood.2
 |
| Mechanisms of Allergic Response |
The purpose of the research conducted by
Hoskin-Parr et al. was to determine the relationship between antibiotic
exposure in patients two years old and younger and the development of allergic
diseases by the age of 7.5 years old.1 The study sought to determine
if certain variables, time of exposure and number of exposures, had an effect.
The research also compared the relationships for three different allergic
diseases, asthma, eczema, and hay fever.
To gather data, the researchers
administered questionnaires to mothers of infants. The questionnaires were
given when the baby was 6 months, 15 months, and 24 months old. The mothers
were asked to report if the child had taken antibiotics once, more than once,
or never since the last questionnaire (or since the child was born, for the
first questionnaire). Each mother was asked to report about her child’s health
again once he or she reached the age of 7.5 years old.
This
study found that children who received at least one dose of antibiotics during
infancy were more likely to have been diagnosed with asthma compared with those
who were never treated with antibiotics by the time they were two years old.1
This effect was stronger as the number of doses received increased. Additionally,
the results suggest that cumulative exposure to antibiotics may be more
important than exposure during any specific time period. The same associations
were found for eczema and hay fever, but effect sizes were weaker.1
Girls were less likely than boys to develop asthma or hay fever, but more
likely to develop eczema. Also, children of non-white ethnicities were more
likely to develop each of the allergic diseases studied compared to their white
counterparts.1
The
scientists had to account for two important factors in order to fully evaluate
the efficacy of their findings: reverse causation and confounding variables. The
researchers included many additional variables to account for confounders. Some
variables, such as sex, ethnicity, and birthweight of the child, would not seem
like they would have much of an effect on the findings. Other variables,
including birth mode (vaginal or Caesarian), breastfeeding, time spent
outdoors, mother’s smoking, and contact with felines, are more interesting
choices, because there are implications for how such factors could directly
effect aspects of immune function.
To account for reverse causation, data
was adjusted to exclude children who were reported to experience wheezing
anytime from birth to 18 months old, and from birth to 30 months old, for which
they possibly received antibiotics.1 This is because these children
may not have developed asthma symptoms at an early age because they were given
antibiotics, but were given antibiotics because of the appearance of the
wheezing. This would be a case of reverse causation.
After
adjusting the model for confounding variables, effect sizes for the study’s
findings remained relatively the same. This means that none of the factors made
a significant difference in the strength of the associations between antibiotic
use and the development of allergies. However, when the patients who showed
signs of wheezing by the time they were 18 months old were eliminated from the
analysis, the significance of the findings was decreased. When those who
experienced any wheezing before they reached the 30-month mark were eliminated,
the associations were even more weakened. This suggests that at least a portion
of the patients whose data contributed to the relationship could be attributed
to reverse causality. Therefore, inappropriate administration of antibiotics
(which is known to be an issue in today’s society) to treat wheeze could result
in an unauthentic association between antibiotic use in young children and
later asthma.1
This
study is one of many that have had difficulty with showing the significance of
its findings in the context of immunology. Many other studies have attempted to
explain how antibiotics could attribute to the development of allergic diseases,
but so far, none of them have had very clear results. Some of the most
important suggestions for the development of allergies are the hygiene
hypothesis and the important role of commensal bacteria in the GI tract. Past
research has shown that children who grow up on farms (and are more likely to
be exposed to a greater variety of bacterial germs) are less likely to develop
asthma and other allergies as compared to children who are raised in rural
areas but not on farms.3 This could be because exposure to microbial
products as youth decreases Th2-biased responses characteristic of allergies.1
Overall, the immunological complexities that lead to the development of
allergic diseases in individuals are not totally understood, but studies such
as the one conducted by Hoskin-Parr et al. suggest that there may be a
dose-dependent relationship between antibiotic use in young children and the
development of allergic responses in these children later in life.
Primary Source:
1. Hoskin-Parr
L, Teyhan A, Blocker A, & Hendeson AJW. (2013). Antibiotic exposure in the first
two years of life and development of asthma and other allergic diseases by 7.5
yr: A dose-
dependent relationship. Pediatr
Allergy Immunol. Accessed 9 Dec 2013.
Secondary Sources:
2. Ly
MP, Litonjua MA, Gold DR, & Celedon JC. (2011). Gut microbiota, probiotics,
and
vitamin D: interrelated exposures influencing allergy, asthma, and obesity?
J Allergy Clin Immunol.
127: 1087-1094.
3. Genuneit
J. (2012). Exposure to farming environments in childhood and asthma and wheeze
in rural populations: a systematic review with meta-analysis. Pediatr Allergy Immunol. 23: 509-518.
*
“Antibiotics.” Medline Plus. U.S. National Library of Medicine. National Institutes of Health. Updated
27 Nov 2013. Accessed 9 Dec 2013. <http://www.nlm.nih.gov/medlineplus/antibiotics.html>.
# Nordqvist, Christian.
“What Are Antibiotics? How Do Antibiotics Work?” Medical News Today. Published 30 Apr. 2009. Updated 24 Nov. 2013.
Accessed 9 Dec. 2013. <http://www.medicalnewstoday.com/articles/10278.php>.
$ “Antibiotics Could Be
the Cause of Many Allergies.” NewsMedical.
Published 27 May 2004. Accessed 9 Dec. 2013. <http://www.news-medical.net/news/2004/05/27/1969.aspx>.
+ Mustafa,
Syed Shahzad. “Allergy: What causes allergies?” MedicineNet. Reviewed 26 Nov. 2013. Accessed 9 December 2013. <http://www.medicinenet.com/allergy/page2.htm#what_causes_allergies>.
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