In what may not make for the sexiest headline, a new study shows there’s a link between constipation and kidney disease.

In the study, researchers examined health records from more than 3.5 million U.S. veterans, looking at whether they reported being constipated or had used laxatives over period of about seven years. They found that those who had experienced constipation had higher risks of developing chronic kidney disease and kidney failure than those who had not.

They also found that the more severe the participant’s constipation, the higher their risk of developing these kidney conditions.

“We cannot really say that we were very surprised,” said Dr. Csaba Pal Kovesdy, chief of nephrology at the Memphis VA Medical Center and one of the study’s co-authors. Previous studies have linked constipation to cardiovascular problems, and the researchers suspected that the same mechanisms through which constipation negatively affects the cardiovascular system would also negatively affect the kidneys. [The Poop on Pooping: 5 Misconceptions Explained]

The key to the link may lie in gut bacteria: Constipation may be a marker of an altered gut microbiome, Kovesdy said. Changes in the community of microbes that live in people’s guts have been linked to numerous metabolic changes, such as increased inflammation.

Although the researchers said they were not yet sure of the exact mechanism that may connect constipation and kidney disease, they suggested that the changes in gut bacteria that cause constipation could also cause food to pass through the digestive system more slowly than usual. This slowdown may lead to chronic inflammation, which in turn may contribute to kidney disease.

Constipation affects about 30 percent of the general population at some point during their lifetime, and is “one of the most prevalent conditions encountered in primary care settings,” the researchers wrote in the study, published today (Nov. 10) in the Journal of the American Society of Nephrology. Elderly people and women are most heavily affected.

Constipation could be a cause of kidney disease, or it may be a sign of other factors that lead to kidney disease. Further research is still needed to determine whether treating constipation could help prevent chronic kidney disease or kidney failure, the researchers said.

The findings could have clinical implications, they said. For instance, physicians may choose to treat their patients with constipation through methods other than laxatives — such as probiotics or a fiber-rich diet — if it turns out that the dehydration that laxatives can cause is a significant link between constipation and kidney disease. [8 Tips to Be a Probiotic Pro]

The researchers noted that their study had limitations: The participants were predominantly male (93.2 percent), and their average age was 60, so researchers cannot yet say whether the same effects would be seen in other populations.

The study is also observational, and so it is not possible to determine a cause-effect relationship between constipation and kidney disease from this data alone. Further studies should be done to pinpoint the exact mechanism that may link constipation and kidney disease, the researchers said.