Long-term use of antibiotics raises the risk of heart attacks and strokes in women, a major study has found.
Scientists believe the discovery is linked to the way the drugs wipe out “good” probiotic bacteria in the gut.
Women over 60 who used antibiotics for two months or more were 32% more likely to develop heart and artery disease than those not taking the drugs, the research showed.
The risk increase reduced with age, falling to 28% for middle-aged women. Younger women aged 20 to 39 were not affected.
The findings come from a large US study that recruited almost 36,500 women whose progress was monitored for an average period of nearly eight years.
Over this period, 1,056 participants developed cardiovascular disease.
The absolute risk of suffering a heart attack or stroke remained relatively small, the scientists pointed out.
Among women in the greatest risk group taking antibiotics for at least two months, six per 1,000 would be likely to experience damage to their hearts or arteries.
Study author Dr Yoriko Heianza, from Tulane University in New Orleans, said: “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 alter the balance of the gut ecosystem, destroying beneficial bacteria and increasing the prevalence of viruses, harmful bugs and infectious fungal organisms such as Candida.
Professor Lu Qi, director of the Tulane University Obesity Research Centre, said: “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.”
The study, published in the European Heart Journal, is the largest over-time investigation of the link between antibiotic use and heart disease ever carried out.
All the participants were enrolled in the Nurses’ Health Study, which has been running in the US since 1976.
The most common reasons for the women taking antibiotics were lung infections, urinary tract infections, and dental problems.
Prof Qi added: “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.”