A long-held theory that antibiotic use in the first year of a child's life can cause asthma may have been disproved. A study published in The Lancet today explains that although children who use antibiotics are indeed at increased risk for asthma, the antibiotics themselves might not be at fault. Rather, the reason for the connection might have to do with the presence of genetic variants on a specific region of chromosome 17.

To reach this conclusion, scientists examined data from the Manchester Asthma and Allergy Study, a study that followed over 1,000 kids from the moment they were born until they turned 11. The researchers found that two genes on chromosome 17 were associated with an increased risk of antibiotic use in the first year of a kid's life. Moreover, kids who were prescribed antibiotics early on tended to have impaired antiviral immunity later in life. But the researchers did not find a link between the development of allergies and early antibiotic use in children — a finding that would have supported the idea that antibiotics alter gut flora and damage a child's immune system.

Given these results, the researchers conclude that although children who receive antibiotics early on really do tend to develop asthma later in life, genetic variants on chromosome 17 might be the underlying cause. This would mean that the link between antibiotics and asthma might actually be the perfect example of the difference between correlation and causation.

The researchers acknowledge, however, that this is only a preliminary finding. Besides antibiotics, a number of other factors have been associated with asthma, including obesity, allergies, and sedentary lifestyles. This means that a lot more work will have to be carried out before scientists can definitely link these genetic variants with asthma. And unfortunately, demonstrating the link with absolute certainty may not be possible at this time, because an exhaustive study on the issue — one that would prevent a large number of children from taking antibiotics in the first year of their lives to see if they later develop asthma — would likely be deemed unethical.