A new meta-analysis, using data from hundreds of thousands of individuals, finds that gallbladder disease and heart disease are more intertwined than previously thought. The reasons behind this connection are, as yet, unclear.

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Gallstones' links to heart disease run deeper than previously thought.

Gallstones are small, hard deposits that form in the gallbladder - an organ that sits below the liver.

In wealthier countries, they are a common occurrence, affecting 10-15 percent of all adults.

Gallstones are thought to be produced due to an imbalance in the makeup of bile - a digestive aid produced by the liver and concentrated in the gallbladder.

Although generally small and often symptomless, over the years, gallstones can grow to the size of pebbles.

Once enlarged, they can block the bile ducts and cause severe abdominal pain, known as biliary colic.

Research, published this week in the journal Arteriosclerosis, Thrombosis and Vascular Biology, investigates the connection between gallstones and heart disease.

Although the two conditions seem, at first glance, to be separate - one is related to the circulatory system, the other is a digestive system-based illness - the links between them are, in fact, deeper than expected.

Gallstones and heart disease

The risk factors for gallstones and heart disease are very similar; they include obesity, diabetes, high blood pressure, poor diet, and high cholesterol. However, the similarities between the two, according to researchers from Tulane University in New Orleans, LA, run deeper than the specific risk factors involved.

A team, led by Dr. Lu Qi, professor of epidemiology at Tulane, carried out a meta-analysis of more than 840,000 participants, including more than 50,000 cases of coronary heart disease. They looked at the relationship between coronary heart disease and the development of gallstones.

The analysis showed that a history of gallstone disease was associated with a 23 percent increase in the risk for coronary heart disease.

"Our results suggest that patients with gallstone disease should be monitored closely based on a careful assessment of both gallstone and heart disease risk factors. Preventing gallstone disease may also benefit heart health."

Dr. Lu Qi

In a second analysis of more than 260,000 participants, Dr. Qi found that heart disease was commonly seen alongside gallstone disease because of the shared risk factors. This was not, perhaps, particularly surprising.

Interestingly, in the second analysis, Dr. Qi also found that individuals with gallstones who were otherwise healthy (not obese, normal blood pressure, and non-diabetic) still had a higher risk of developing coronary heart disease than those who were diabetic, obese, and had high blood pressure.

In other words, regardless of the risk factors for the two conditions, simply having gallstones alone is enough to increase heart disease risk.

The results back up previous studies with similar findings. However, previous studies have been less convincing - for instance, they were carried out in populations outside the United States, did not confirm gallstone diagnoses, or used smaller sample sizes.

For the first time, a large-scale study has shown that the presence of gallstone disease raises heart disease risk without the presence of traditional risk factors.

Why are gallstones linked to heart disease?

The meta-analysis could not identify the reasons behind this relationship, but there are a number of potential mechanisms. One theory is that gallstones alter bile acid secretion, which has previously been linked to cardiovascular events.

Medical News Today asked Dr. Qi which theory he backed, he said:

"Gallstones affect secretion of bile acids, which play a key role in regulating gut microbiota. [...] there are growing data suggesting potential links between gut microbiota, bile acids, and cardiovascular disease."

He hopes that these results will be followed up with clinical trials to reach a deeper understanding of the links between the two conditions. Because the way in which gallstones affect heart health is not clear, getting a deeper understanding could help in the treatment, prevention, and management of both.

MNT also asked Dr. Qi if he has plans to follow the results up himself. "We are going to investigate whether gallstone disease is related to other diseases such as diabetes, and mortality," he replied.

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