New Orleans, LA—Taking antibiotics over an extended period of time can increase risk of cardiovascular events in women.

That’s according to a large study published in the European Heart Journal involving nearly 36,500 women.

The Tulane University–led study determined that women aged 60 years or older who took antibiotics for 2 months or more had the greatest risk of cardiovascular disease (CVD). Some increased risk also was identified in middle age patients aged 40 to 59 years but not in younger adults aged 20 to 39 years, according to the report.

“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,” explained Lu Qi, PhD, director of the Tulane University Obesity Research Centre, Tulane University, New Orleans, and adjunct professor of nutrition at Harvard T.C. Chan School of Public Health, Boston.

To provide more information, the study team investigated associations of life-stage and duration of antibiotic exposure during adulthood with subsequent CVD events.

Included were 36,429 women initially free of CVD and cancer from the Nurses’ Health Study. Researchers estimated hazard ratios (HRs) for CVD—a composite endpoint of coronary heart disease or stroke—according to duration of antibiotic use in young (aged 20–39 years), middle (aged 40–59 years), and late (aged 60 years and older) adulthood.

Over an average of 7.6 years of follow-up, 1,056 participants developed CVD, with results indicating that women with long-term use of antibiotics, defined as 2 months or longer, in late adulthood had a significantly increased risk of CVD (HR 1.32, 95% CI, 1.03-1.70) versus women who did not use antibiotics in this life stage.

The study adjusted for covariates including demographic factors, diet, and lifestyle, reasons for antibiotic use, overweight or obesity, disease status, and other medication use.

“In this study which examined the antibiotic use in different life-stages, longer duration of exposure to antibiotics in the middle and older adulthood was related to an increased risk of future CVD events among elderly women at usual risk,” study authors write. “Longer duration of antibiotic use in middle adulthood was also related to higher risk of CVD (P trend = .003) after controlling for these covariates. There was no significant relationship between the use in young adulthood and the risk of CVD.”

Researchers calculate that, among women who take antibiotics for 2 months or more in late adulthood, six women per 1,000 will develop a CVD, compared with three per 1,000 among women who had not taken antibiotics.

“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,” noted first author Yoriko Hejanza, PhD, RD. “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.”

Among study participants, the most common reasons for antibiotic use were respiratory infections, urinary tract infections, and dental problems.

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