All the good antibiotics can do if they rely too much on them. In particular, their excessive use can help to form bacterial superbugs against future antibiotics. However, a new study published this week in JAMA Psychiatry suggests that the use of antibiotics, at least in young people, has a more subtle consequence: a higher risk of developing severe mental illnesses such as obsessive-compulsive disorder and schizophrenia.
Scientists' interest in the idea that frequent infections could raise the risk of developing Alzheimer's in previous years has been reawakened. However, researchers have also found evidence that infections in children can increase the risk of mental illness even earlier. A common hypothesis underlying both theories is that these infections can cause chronic inflammation or other physical side effects that directly harm the brain. Study author Robert Yolken, a neurovirologist at the Johns Hopkins University School of Medicine, and his team decided to find another possible explanation for why infections are related to a mental illness.
Yolken has speculated that changes in the intestinal microbiome – a living sea of bacteria that our digestive system calls home – can also damage the brain. The gut microbiota helps to coordinate the gut-brain axis, a complex communication network of hormonal and nervous signals between the gut and brain that regulates the body. And one of the most devastating ways to alter the microbiome is to take antibiotics, many of which indiscriminately kill both harmless and disruptive bacteria.
Therefore, Yolken and his Dutch counterparts examined the medical history of all born Danish residents between 1995 and 2012, just over a million children. They specifically looked at children who had taken antimicrobial drugs, almost always antibiotics, for an infection before the age of 18 years. Thereafter, they followed their mental health for an average of ten years. They also compared their fate with a control group of Danish children who had been given germ-drugs but for whatever reason were not received (one common reason could be that these children did better on their own before the parents joined them would have gone the local pharmacy).
"What we basically found out was that exposure to antibiotics, especially long-term antibiotics or multiple doses of antibiotics, has been linked to an increased risk of a range of different psychiatric illnesses," Yolken told Gizmodo.
Only 3.9 percent of the children, a total of about 42,000, were later hospitalized and diagnosed with a mental disorder, while 5.2 percent and 56,000 children later received prescriptions for an antipsychotic. Compared to untreated children, children who had been given antimicrobial agents had a significantly higher likelihood that either would happen to them.
Children who were hospitalized and treated for infection were 84% more likely to be hospitalized for mental illness and 42 percent more likely to be given antipsychotics. But even children who only had antibiotics prescribed for infection were still 40 percent and 22 percent, respectively, hospitalized for mental illness or given antipsychotics. In both scenarios, the highest associated risk was seen in children with antibiotics, while no additional risk was seen in children receiving antiviral or antifungal medications.
"This should not panic anyone. If we talk about parents whose children are getting antibiotics because of an ear infection, then one dose will not do much. "
The use of antibiotics is obviously not the only factor that affects a person's mental health risk. The team was also able to look at the mental health history of the siblings of the treated children. Compared to siblings, the children treated had a higher risk of mental illness, but to a lesser degree than the general public. In other words, a person's common genetics or environment also seems to play a role in making them susceptible to mental illness.
Yolken also does not rule out that infections themselves, especially life-threatening ones, can sometimes still harm the brain directly. But if you look at minor infections, the antibiotics are probably a bigger factor.
A population study like this can not prove that A causes B or vice versa, but only an indirect connection between them. The study, Yolken says, is the largest and most comprehensive of its kind. And Yolken and others hope to continue animal research that can directly identify how an antibiotic-damaged gut microbiota can increase the risk of mental illness.
When talking about parents whose children are getting antibiotics because of ear infection – one dose will not do much, "Yolken said. "But at the population or medical level, I think it's important to limit the antibiotics that we receive in our childhood, especially in the first or second year of life."
Due to the growing resistance to antibiotics, some doctors and hospitals are already making a special effort to reduce or better inform the use of antibiotics. Too many doctors, sometimes at the request of patients, tend to prescribe antibiotics when they are not needed or useful, either because the infection is short-lived and mild, or because it is not caused by bacteria. These reforms include writing fewer prescriptions of antibiotics, shortening treatment duration, or using lower-spectrum drugs that can affect only a few types of bacteria.