Published in the European Heart Journal, antibiotic use over a long period of time can increase the risk of heart attack or stroke in women.
The study found that women aged 60 or older who took antibiotics for two months or more had the greatest risk of heart attack or cardiovascular disease, but long duration of antibiotic use was also associated with an increased risk if taken during middle age (aged 40-59). The researchers could find no increased risk from antibiotic use by younger adults aged between 20-39.
Investigating antibiotic use
Professor Lu Qi, director of the Tulane University Obesity Research Centre, Tulane University, USA, and adjunct professor of nutrition at Harvard T.C. Chan School of Public Health, USA, who led the research, says that a possible reason why antibiotic use is linked to an increased risk of cardiovascular disease is because antibiotics alter the balance of the micro-environment in the gut, destroying “good” probiotic bacteria and increasing the prevalence of viruses, bacteria or other micro-organisms that can cause disease.
“Antibiotic use is the most critical factor in altering the balance of microorganisms in the gut. Previous studies have shown a link between alterations in the microbiotic environment of the gut and inflammation and narrowing of the blood vessels, stroke and heart disease,” he said.
A study of 36,429 women
The researchers studied 36,429 women who took part in the Nurses’ Health Study, which has been running in the USA since 1976.
After adjustments to take account of factors that could affect their results, such as age, race, sex, diet and lifestyle, reasons for antibiotic use, overweight or obesity, other diseases and medication use, the researchers found that women who used antibiotics for periods of two months or longer in late adulthood were 32% more likely to develop cardiovascular disease than women who did not use antibiotics. Women who took antibiotics for longer than two months in middle age had a 28% increased risk compared to women who did not.
These findings mean that among women who take antibiotics for two months or more in late adulthood, six women per 1,000 would develop a cardiovascular disease, compared to three per 1,000 among women who had not taken antibiotics.
Finding the association regarding the increased risk of heart attack and stroke
The first author of the study Dr Yoriko Heianza explains: “By investigating the duration of antibiotic use in various stages of adulthood we have found an association between long-term use in middle age and later life and an increased risk of stroke and heart disease during the following eight years.
“As these women grew older, they were more likely to need more antibiotics, and sometimes for longer periods of time, which suggests a cumulative effect may be the reason for the stronger link in older age between antibiotic use and cardiovascular disease.”
Antibiotics should only be used when absolutely needed
The most common reasons for antibiotic use were respiratory infections, urinary tract infections and dental problems.
The study is the largest prospective study to investigate the link between antibiotic use and risk of heart disease and stroke, and this is one of the strengths of the study, as well as the long follow-up and comprehensive information on factors that could affect the results such as life style, diet, age, other diseases and medication use.
Qi concluded: “This is an observational study and so it cannot show that antibiotics cause heart disease and stroke, only that there is a link between them. It’s possible that women who reported more antibiotic use might be sicker in other ways that we were unable to measure, or there may be other factors that could affect the results that we have not been able take account of.
“Our study suggests that antibiotics should be used only when they are absolutely needed. Considering the potentially cumulative adverse effects, the shorter time of antibiotic use the better.”