A comprehensive study involving over 6 million children reveals that those exposed to antibiotics prenatally or in early childhood do not generally face a heightened risk of developing autoimmune disorders during adolescence. However, the dynamics are quite intricate.

The notion that antibiotics may lead to autoimmunity dates back to the 1980s. David Strachan later proposed that the London’s Faculty of Hygiene and Tropical Medicine illustrates fewer infections in cleaner environments leading to a higher rate of childhood allergies.

This line of thought gave rise to the hygiene hypothesis, suggesting that limited early exposure to specific microorganisms fails to adequately train the immune system, which may react excessively to benign substances, leading to allergic responses or autoimmune disorders. Conditions like type 1 diabetes, inflammatory bowel disease, and lupus occur when immune cells mistakenly target the body’s own tissues.

Numerous studies since have demonstrated the crucial role of various microorganisms, particularly gut microbes, in shaping our immune responses. For instance, essential compounds for the maturation of specialized immune cells, such as regulatory T cells, play pivotal roles in preventing autoimmunity. This raises concerns over whether antibiotics that disrupt gut microbiota could facilitate the emergence of autoimmune diseases.

“Over time, numerous clinical studies, primarily using animal models, have substantiated the idea that antibiotics, or modifications to the gut microbiome, significantly affect immunity,” states Martin Kriegel from the University of Munster, Germany.

For instance, a 2016 study on mice illustrated that repeated antibiotic treatment at early life stages increased susceptibility to type 1 diabetes. Mice with genetic predisposition to this disorder were given their mothers’ breast milk alongside antibiotics thrice at 4 and 5 weeks old. Approximately 50% of the male and 80% of the female mice in this group developed type 1 diabetes by 30 weeks, while only about 25% of the male mice and 50% of the female mice that avoided antibiotics faced the same issue.

Similar correlations have surfaced in human research. An evaluation of over 10 million individuals released this year indicates that those prescribed antibiotics face an 40% higher risk of later developing inflammatory bowel disease. Additionally, a 2019 study involving over 110,000 participants linked antibiotic prescriptions to a 60% increased risk of developing rheumatic arthritis.

Conversely, other studies denote contrary findings. For example, a 2017 study involving over 15,000 children assessed for type 1 diabetes and celiac disease found no correlation between these conditions and antibiotic use prior to the age of four.

Recently, Eun-Young Choi from Sungkyunkwan University in Korea and her colleagues tracked the onset of six autoimmune conditions: type 1 diabetes, chronic pediatric arthritis, ulcerative colitis, Crohn’s disease, lupus, and Hashimoto’s disease. Around 1.5 million mothers received antibiotics during pregnancy, and a second group of 3.4 million children received similar treatment within the first six months post-birth, with 1.9 million treated with antibiotics.

After adjusting for variables like infection type, socioeconomic status, and gender, researchers found no collective correlation between antibiotic exposure in utero or early childhood and the likelihood of developing autoimmune conditions in adolescence.

Why do these findings differ so greatly? The gut microbiota’s complexity plays a significant role. Various factors influence it, making holistic explanations challenging. For instance, the studies referenced may fail to account for dietary influences on gut microbiota.

Different antibiotics also provoke varied effects. Choi’s study established a connection between broad-spectrum antibiotic use during pregnancy and subsequent development of Crohn’s disease in children. Additionally, the timing of antibiotic exposure appeared critical; antibiotics administered within two months of birth correlated with a 30% increased risk of Hashimoto’s disease.

This doesn’t imply that antibiotics should be entirely avoided. “When antibiotics are deemed necessary during pregnancy, it’s due to a belief that their benefits surpass potential risks,” asserts Christopher Zahn from the American University of Obstetricians in Washington, DC. For example, urinary tract infections can result in severe issues like preterm birth and low birth weight.

In fact, certain antibiotics may thwart autoimmunity. A 2018 study discovered that infections from pathogenic bacteria, notably Enterococcus gallinarum, induced autoimmunity in mice. Antibiotic treatment not only prevented mortality but also inhibited immune cells from attacking the organisms’ tissues.

“Thus, the situation is immensely complicated,” remarks Kriegel.

However, the latest findings should alleviate concerns for pregnant individuals and those with young children, reassures Zahn.