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Woman holds a pill up to her mouth in order to take it. She holds a glass of water in her other hand.
People may need to take long-term antibiotics for a range of conditions. fizkes/ Shutterstock

Long-term antibiotic use by middle-aged women may affect cognitive function – new study

Antibiotics are one of the most commonly prescribed drugs in the world. They’re used to treat many different bacterial infections. While most people may only be on a course of antibiotics for a week or two at a time, some may take antibiotics for a longer period to treat certain chronic conditions, such as pneumonia or acne.

While antibiotics can be life-saving, long-term use can come with several side effects – not least of which is the risk of bacteria developing antibiotic resistance. And now, a recent study has also linked long-term antibiotic use by middle-aged women to an increased risk of cognitive decline.

To conduct their study, the researchers collected data from 14,542 participants who had taken part in the Nurses’ Health Study II. This study monitored the health and wellbeing of nurses every two years between 2014-2018. The average age of participants at the start of the study was 54.

The researchers recorded the participants’ antibiotic use up to four years prior to the start of the study. Some women had taken long-term antibiotics (two months or more) for a variety of conditions – such as respiratory problems or acne. Others had not been prescribed any antibiotics. The researchers measured cognitive ability using online tests that participants completed, which measured factors such as learning and working memory.

The women were followed up seven years later to see whether long-term antibiotic use in middle-age had lasting effects on cognition. Women who had previously used long-term antibiotics scored lower on learning, working memory, motor speed and attention tests compared to non-users. It’s unknown whether short-term antibiotic use had a similar effect as this wasn’t reported.

Gut health

Though the findings only show a link between antibiotic use and cognitive decline, the researchers think that gut microbiome changes caused by long-term antibiotic use may be the reason some women experienced poorer cognitive function.

Our bodies contain millions of tiny microbes invisible to the human eye. These bacteria and viruses quietly keep our health in check. But many things can disturb our microbiome’s balance – including poor diet and antibiotic use.

Woman holds an antibiotic pill between her thumb and index finger.
Antibiotics can disrupt our gut microbiome. Joe Besure/ Shutterstock

While antibiotics kill bacteria that cause infections in our body, they can also may kill other bacteria, including helpful ones. Even a small disruption in our microbiome’s balance can have an impact on our health – linked to conditions such as inflammatory bowel disease, type 2 diabetes, obesity and mental health problems.

Our gut microbiome and brain are also connected, which is why a healthy gut is important for brain health. For example, the proteins our brain cells use to communicate are manufactured by gut microbes. When the gut microbiome becomes unbalanced these proteins become damaged. Not only does this affect how our brain works, it may even contribute to conditions such as dementia, Parkinson’s disease and even schizophrenia.

Given the microbiome’s connection to brain health and cognition and extensive evidence which shows antibiotics can disrupt the microbiome, it seems plausible that long-term antibiotic use can affect the cognitive functions of the brain. For example, there’s evidence antibiotic use in early childhood – an important time for brain and cognitive development – can have negative effects on cognition up to 11 years later.

Though few studies have measured both antibiotic use and cognitive function in adults, some studies have shown broad-spectrum antimicrobials (including antibiotics) can affect our cognitive function – causing side effects such as confusion, delirium and poorer attention in both men and women, even after short-term use.

While this recent study showed a link between long-term antibiotic use and cognitive decline, the study has some of limitations to take into account. First, the online cognitive test only assessed four functions. This means we don’t have a full picture of cognitive health, and we do not know if there are other cognitive deficits in addition to those measured in the study.

Another shortfall is that researchers did not collect faecal samples. This means we don’t actually know whether the microbiome changed significantly after long-term antibiotic use – and whether this change persisted. Though the researchers were able to show that antibiotic use had a greater link to poorer cognitive function than other lifestyle factors (such as diet, or other health conditions), it will still be important for future research to look at whether the microbiome really plays a role in antibiotic use and cognitive function.

The age of the participants is also an important factor, as the average age was 54 at the start of the study – which is the time most women experience menopause. Menopause causes hormonal changes that can affect everything from how the immune system works, sleep quality, weight, blood pressure and even concentration and thinking.

Some research also shows that the menopause alters the microbiome. As such, it will be important to future studies to include men in mid-life to see whether they show similar effects.

These research findings indicate that it’s important to pay attention to gut health at all stages of life. Fortunately, there are many things you can do to make your microbiome healthier – such as eating a high-fibre diet and using prebiotics and probiotics. Fresh air and exercise also have positive effects on the microbiome. Of course for persistent problems medical attention should be sought.

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