Anxiety, increased blood pressure, heartburn and 'the jitters' may come to mind when people think of consuming too much coffee.
But what happens to your liver?
For decades, experts have associated coffee consumption with a reduced risk of liver disease. But things like recall bias and lifestyle factors have likely impacted these findings.
This notion inspired Elliot Tapper, M.D., an associate professor of internal medicine at Michigan Medicine, to team up with liver specialists from Harvard Medical School and study the effects of coffee consumption on liver health without including external influences. Their findings were published in Clinical Gastroenterology and Hepatology.
The team used the National Health and Nutrition Examination Survey, or NHANES, to examine a total of 4,510 individuals that were aged 20 years or older and did not have viral hepatitis. Each qualifying participant also had a complete elastography exam.
"It's important to recognize that there are multiple ways to understand the health of someone's liver," said Tapper. "There are blood tests that can provide clues, but they're neither sensitive nor specific. There are also liver biopsies that are much more invasive, but it's difficult to study an entire population this way."
Therefore, Tapper and his team decided to use the elastography exam to "literally assesses the elasticity of the liver, revealing its stiffness. Because traditionally, the stiffer the liver, the unhealthier it is."
The exam uses technology comparable to that of an ultrasound and measures liver stiffness by observing a wave of movement that travels through the liver.
"The liver is jiggled, so to speak, and the speed of its movement is interpreted as its stiffness," said Tapper. "This all happens through the skin, with a probe going through the rib area which then triggers the wave of movement within the liver."
The team compared caffeinated coffee to decaffeinated coffee and tea. They also adjusted for things like sugar-sweetened beverage consumption and lifestyle factors within their pool of participants.
"When patients are diagnosed with liver disease, they'll often ask their physicians about dietary modifications," said Tapper. "For example, 'What should I eat or not eat, drink or not drink, in order to get better?'"
While the answer to these questions usually focuses on whole foods and vegetables, there also have been many years of research around coffee consumption and associations with healthier livers.
However, Tapper noted that correlation is not causation and these data suffer from "recall bias, healthy-user bias, and indirect measures of liver outcomes or health."
Therefore, it was important for Tapper and his colleagues to examine the highest quality nutritional information for their study participants through a direct assessment of their liver health.
The results
The team found that individuals who consumed more than three cups of coffee a day showed reduced levels of liver stiffness when lifestyle factors were considered. They also found that these same individuals experienced reduced risks associated with increased liver stiffness.
"While coffee consumption was associated with a lower risk of elevated liver stiffness, this didn't include fatty liver disease, or steatosis," said Tapper. "Overall, our findings showed that if coffee has an effect on the liver, it is likely by reducing fibrosis, or scar tissue."
Tapper added that he hopes that this study will shine a light on the burden of chronic liver disease in the United States, even when individuals may not necessarily know that they have it.
"Our research revealed the importance of looking for this condition," he said. "It also gives us something to discuss with our patients who may want to do something extra to help their livers. It highlights the value of conducting a complete nutritional assessment with our patients, as liver specialists and health care providers. If something as simple as consuming coffee can reduce liver cancer or symptoms of cirrhosis, there is a critical need for us to explore this topic further in trials."
Paper cited: "Coffee consumption is associated with lower liver stiffness: a nationally representative study," Clinical Gastroenterology and Hepatology. DOI: 10.1016/j.cgh.2021.09.042