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Wednesday, July 20, 2011

Increased Risk of Childhood Asthma From Antibiotic use in Early Life

The rates of asthma have increased all over the world but especially in industrialized countries with clean water and better health care systems. Several theories are being studied to try to understand the cause of this.

The “Hygiene Hypothesis” stems from a belief that growing up in cleaner environments affects the development of a child’s immune system differently than growing up in an environment with more bacteria. That is why children who grow up in the country or on farms seem to have lower rates of asthma than children who are raised in the city. 

Researchers also think that the presence of microbes in our intestines helps our immune system to develop properly and that the use of antibiotics early in life disturbs the amount of normal gut microbes. This then affects the development of a baby’s immune system. 

Our research questions:
  • Does taking antibiotics in the first year of life affect the chances of a child developing asthma by age 7 years?
  • Are these results different for children living in the city vs children living in the country?
  • Are all antibiotics associated with changes in the rates of asthma?

Antibiotics were divided into 2 groups, Broad spectrum (BS) and Narrow spectrum (NS).

Broad spectrum antibiotics are antibiotics that can kill a large range of different bacteria. Examples of broad-spectrum antibiotics are: Amoxicillin, Ampicillin, Tetracycline, Chloramphenicol, and Ciprofloxacin.

Narrow spectrum antibiotics are active against a select group of bacteria. Examples of Narrow spectrum antibiotics are: Penicillin, Cloxacillin, Cephalexin, Cefadroxil, and Erythromycin.

Researchers also looked at other risk or protective factors and divided groups of children according to: gender, rural vs urban living environment, family income, family history of asthma (mother with asthma) and the number of children in the home.

65% of children in the SAGE study received at least one prescription for antibiotics during their first year of life.
- 52% had received a broad spectrum antibiotic only
- 3% had received a narrow spectrum antibiotic only
- 10% had received both types of antibiotics

Illnesses treated with antibiotics include:
- Ear infections (40%)
- Upper respiratory tract infections (28%)
- Lower respiratory tract infections (19%)
- Non-respiratory tract infections (7%)

  • The use of Broad Spectrum antibiotics in the first ear of life increased the chances of a child developing asthma by age 7.  The more courses of antibiotics a child had, the higher the chance of getting asthma.

  • Children who received more than 4 courses of Broad spectrum antibiotics in the first year were almost twice as likely to get asthma by age 7. 

  • Children most at risk of the effects of antibiotics were children living in the country and children who DID NOT have a dog in the home when they were babies. A possible explanation for this is that children who live in the city and who do not have a dog already have lower levels of bacteria in their gut and that taking antibiotics does not change that much.  In essence, children who are naturally exposed to higher levels of bacteria (eg: those who live on farms or who have pets) have the most to lose. The amount of bacteria in their gut changes more dramatically with antibiotics and their immune system changes accordingly.
  • Children whose mothers did not have asthma also seemed more sensitive to the effects of antibiotics. The reason for this is not understood but may have to do with some inherited genetic difference.

Conclusion: Use of antibiotics in early childhood puts all children at higher risk of getting asthma by age 7 years. Some children are more at risk of this than others. The exact reasons for this are not yet clear. 

Broad spectrum antibiotics seem to increase the risk the most.  More studies need to be done to understand this better. In the mean time, it is suggested that frequent use of Broad spectrum antibiotics be avoided as much as possible in the first year of life.  Doctors continue to be advised to only use antibiotics when absolutely necessary.

Increased risk of childhood asthma from antibiotic use in early life.Kozyrskyj AL, Ernst P, Becker AB. Chest. 2007 Jun;131(6):1753-9. Epub 2007 Apr