Ulcerative colitis, Abe's ailment, is a long-term debilitating disease

Ulcerative colitis, the gastrointestinal disease that debilitated Japanese Prime Minister Shinzo Abe to the point of stepping down, is an inflammatory bowel disease that affects millions and can flare up unpredictably.

It irritates and inflames the innermost lining of the colon and rectum, causing ulcers or sores. Symptoms can include uncontrolled diarrhea, rectal bleeding, weight loss, decreased appetite, abdominal pain, and frequent need to go to the bathroom.

The disease can appear at a young age and worsen over time, as it appears to have happened to Mr Abe, 65. Doctors say they also observed people in their fifties and older who had no symptoms at a young age.

Inflammatory bowel disease also includes Crohn's disease, which can disrupt the entire gastrointestinal tract.

Ulcerative colitis and Crohn's disease combined affect more than two million people in North America, more than three million in Europe, and millions more worldwide. This is based on estimates in an article published in May by Clinical Gastroenterology and Hepatology, a medical journal.

Dr. Ashwin N. Ananthakrishnan, a gastroenterologist at Massachusetts General Hospital who was the lead author of this article, said ulcerative colitis first appeared during the Civil War and has increased dramatically since the 1940s in the US and since the 1970s in Asia, including Japan .

He and other doctors attributed the growth in the cases in part to changes in eating habits – especially a move away from high-fiber diets – especially in Asia. However, the underlying causes and triggers of Crohn's disease and ulcerative colitis remain areas of intense research. Many treatments have been designed to help relieve symptoms, but both diseases can recur without warning.

"It's still associated with a lot of disorders," said Dr. Ananthakrishnan in a telephone interview. "People can have flare-ups that can last a few days to a few weeks."

Dr. Reezwana Chowdhury, an assistant professor at Johns Hopkins University School of Medicine and a specialist in colitis and other bowel diseases, said ulcerative colitis "can develop at any age" and children diagnosed with colitis could have chronic recurrences. "It's a lifelong illness," said Dr. Chowdhury.

Removal of the colon can be seen as a cure for ulcerative colitis, but not without complications. In some cases, surgeons create an artificial opening in the abdominal wall to drain body debris from the small intestine. an operation known as an ileostomy.

Dr. Ananthakrishnan said advances in treatments have greatly reduced the need for surgery. Twenty years ago, he said, one in five patients had to undergo an operation, now one in ten.

Nonetheless, even people who have responded to treatment could have flare-ups, which Mr Abe appeared to do, and it could "affect the functioning of such a high-ranking person".