A Henry Ford Hospital study shows use of antibiotics in babies dramatically increases the risk of allergies and asthma by age 7.
For the Henry Ford study, researchers followed 448 children from birth to seven years. The children were evenly divided by gender.
Data was collected prenatally and at the first four birthdays until the children were 6 and 7 years old, when they underwent a clinical evaluation by a board-certified allergist. The data included information about all prescribed oral antibiotics; blood tests that measure the antibody (immunoglobulin E) that causes allergies; and skin reaction tests that show whether a person is hypersensitive to an allergen. Researchers also collected data on all clinical visits and made home visits to collect environmental samples.
Of the 448 children, 49 percent had received antibiotics in the first six months of life. The most common antibiotic category prescribed was penicillin.
Among the findings:
- By age 7, children given at least one antibiotic in the first six months were 1.5 times more likely to develop allergies than those who did not receive antibiotics. They were 2.5 times more likely to develop asthma.
- By age 7, children given at least one antibiotic in the first six months and who lived with fewer than two pets were 1.7 times more likely to develop allergies, and three times more likely to develop asthma.
- By age 7, children given at least one antibiotic in the first six months and whose mother had a history of allergies were nearly twice as likely to develop allergies.
- By age 7, children given at least one antibiotic in the first six months and who were breast-fed for more than four months were three times more likely to develop allergies. However, breast-feeding did not influence the risk between antibiotics and asthma.
Note that between the second and third bullet items above the only difference was the reduction in pet exposure and the result was a higher incidence of allergies and asthma.
The oddest result that I see is the fourth item where breast-feeding increased the risk of allergies but not of asthma. One potential explanation: the breast milk might cause the immune system of babies to develop more rapidly and hence to be more likely to react to allergens. Given that breast milk probably has other benefits that makes its use a tough call.
Overall, children given antibiotics in their first half-year were 2.6 times more likely to develop allergic asthma, the team told a meeting of the European Respiratory Society on Tuesday. With broad-spectrum antibiotics, which kill a wide range of bacteria, the risk was far higher: children were 8.9 times more likely to suffer from asthma.
Selection of an antibiotic more narrowly tailored for the target bacteria therefore would reduce risk of allergy and asthma among babies.
The new study also backs the growing belief that antibiotics disrupt the normal development of a child's immune system through a phenomenon known as the "hygiene hypothesis."
This "hygiene hypothesis" has been gathering strength in recent years. The latest result certainly strengthens the argument considerably. The idea is basically remiscent of the saying "idle hands are the devil's workshop". Remove the normal antigens that the immune system is exposed to and it starts reacting to things it ought not react to. Our ancestors lived in dirt floor dwellings and had much more exposure to animals, dirt, and nature in general. We live lives which bring us in much less exposure to the antigens we evolved to deal with. Exposure to those antigens appear to be necessary to instruct the immune system on what it should identify as a threat.
From a signal processing perspective you can think of the immune system as a sensor system that will incorrectly react to weaker signals in the absence of stronger signals to react to. The immune system never experienced enough evolutionary pressure to not react to weaker signals because there were so many stronger signals around for it to pay attention to.
Surely antibiotics are overused and this latest report is yet another reason to reduce the use of antibiotics in situations where they are not necessary. But some children will inevitably get bacterial infections in their early months of life that require antibiotic treatment. So what to do about this problem? One potential solution is to develop vaccines that will retrain the immune system to not react to allergens. It may some day be standard practice to give babies anti-allergy vaccines.
In the shorter term having dogs licking babies faces may be a good thing. Also, it might be possible to come up with formulations of beneficial bacteria to give to babies to replace normal harmless bacteria that are wiped out by antibiotic therapy.
The argument that cleaner environments cause problems in the immune system is especially interesting because it demonstrates how moving humans out of the environments they evolved in creates problems that can be quite subtle and that can go unrecognized for many years. This is not the only such problem of this sort. To take another but rather more obvious example, the higher incidence of obesity in affluent nations is a problem that has arisen because of the lifestyles that are the result of living in industrial societies. Obesity is even more interesting than the allergy/asthma problem because obesity is a behavioral problem. Obese people are driven by strong urges to eat more than what is good for them in modern circumstances.
There are other behavioral problems that arise from growing up in industrial society as well. To take another example, humans are obviously not evolved to handle recreational drugs. Recreational drugs interfere with mechanism of pleasure that evolved to guide learning and other activities. Drugs hijack pleasure systems. Many minds become too easily trained to crave the pleasures that the drugs give them and so the pursuit of pleasure becomes far more harmful than it was in our evolutionary past. Humans are going to have to develop methods of adapting themselves to the changes they are creating in their environment.
Update: In another example of the importance of the sensitivity of the immune system to the timing of exposures to various antigens researchers in the United States and Germany have just discovered that the date of first introduction of babies to cereals affects their odds of developing diabetes.
Babies with a family history of diabetes who were introduced to cereals before or after the recommended age of four to six months had a higher risk of developing a precursor to the disease, researchers said Tuesday.
US team lead researcher Dr. Jill Norris says early exposure to cereal proteins may cause an immature immune system to react inappropriately.
She hypothesizes that the youngest babies have extremely vulnerable immune systems. Older babies, denied solids for so long, simply ate more and overwhelmed still developing systems with foreign cereal proteins. The hypothesis has yet to be proved and Norris stressed the scenarios refer to at-risk babies.
Another theory is that children who don't start eating cereals by 6 months of age are more likely to be deficient in vitamins and that this causes their immune systems to malfunction and start making auto-antibodies (i.e. antibodies to ones's own proteins).
|Share |||Randall Parker, 2003 October 01 01:59 PM Biomedical|