Scientists at Tulane University in New Orleans, LA, Harvard Medical School and Harvard T. H. Chan School of Public Health in Boston, MA, and Fudan University in Shanghai, China investigated how antibiotic use is linked to women’s risk of experiencing cardiovascular problems.
They were interested in the link between antibiotics and cardiovascular health because, they explain, antibiotics can have an important impact on gut microbiota, which, in turn, can affect various other aspects of health.
“Antibiotic use is the most critical factor in altering the balance of microorganisms in the gut,” says study co-author Prof. Lu Qi.
“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 adds.
The study — the findings of which appear in the European Heart Journal — analyzes information the scientists collected from a cohort of 36,429 women enrolled in the Nurses’ Health Study.
Specifically, the researchers examined data from 2004–2012; at the beginning of this period, all the women in the cohort were 60 or older.
All the participants reported how often they used antibiotics and other relevant information during three periods of their lives: ages 20–39, ages 40–59, and ages 60 and over.
Based on the antibiotic use patterns that the women reported, the scientists split them into four groups:
- those who had never used antibiotics
- those who took antibiotics for fewer than 15 consecutive days at a time
- those who used antibiotics for between 15 days and 2 months
- those who took antibiotics for over 2 months
‘A cumulative effect’ of antibiotic use?
Over a follow-up period of almost 8 years, on average, 1,056 participants developed cardiovascular problems.
Throughout this period, the women continued to offer information about their antibiotic use every couple of years.
The scientists analyzed the data they took throughout this time, adjusting the results for potentially confounding factors. These included age, race, dietary choices, lifestyle habits, medical conditions, and overall drug use.
Women who took antibiotics for very long periods of time (for 2 months or longer) at age 60 or over had a 32% higher risk of experiencing cardiovascular disease compared with those who had never taken antibiotics.
Those who took antibiotics for 2 months or longer at ages 40–59 were 28% more likely to develop cardiovascular problems than women who did not take antibiotics at that age. However, the team found no correlation between prolonged antibiotic use at ages 20–39 and cardiovascular risk.
“By investigating the duration of antibiotic use in various stages of adulthood,” points out first study author Yoriko Heianza, Ph.D., “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 8 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.”
Yoriko Heianza, Ph.D.
‘The shorter time of use, the better’
The researchers also note that some of the most common reasons women cited for their antibiotic use included infections — respiratory and pertaining to the urinary tract — and oral health conditions.
Though this is the largest prospective study to date that has looked at the correlation between the use of antibiotics for long periods of time and cardiovascular risk, the research was not without its limitations.
For example, the researchers admit that the main problem they faced in this study was the fact that the participants self-reported their use of antibiotics, which tends to leave room for inaccuracies.
However, they also argue that the participants were likely to report fairly precise information, being healthcare professionals themselves.
The scientists are quite confident in their findings, but they explain that the study was observational and cannot, as yet, speak to cause and effect.
“This is an observational study,” notes Prof. Qi, “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 [to] take account of,” he goes on.
Despite these points, Prof. Qi concludes: “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.”