A simple vinegar beverage consumed each morning may offer modest relief for adults with mild constipation, according to new research from Japan. Experts, however, describe the findings as preliminary and caution against treating vinegar as a proven remedy.

Constipation generally means having fewer than three bowel movements each week, according to the National Institutes of Health. It can also involve stools that are hard, dry or lumpy, as well as bowel movements that are difficult or painful.

Chronic constipation can lead to hemorrhoids and anal fissures when left untreated. In severe cases, it may result in fecal impaction requiring emergency care.

The NIH recommends beginning with dietary and lifestyle changes. Those steps include increasing fiber through legumes, whole grains, fruits, vegetables, nuts and seeds, while nonprescription medicines may be used when needed.

The new study, published online in Scientific Reports, examined whether drinking vinegar in liquid form could increase bowel movements. Japanese researchers had previously found that more frequent consumption of dishes containing vinegar was positively associated with better defecation status.

It remained unclear how much vinegar would be needed or whether acetic acid, a potentially active ingredient, was responsible for the apparent benefit. Researchers therefore designed a randomized controlled trial involving healthy adults with mild constipation.

The study included 44 healthy Japanese adults between 20 and 69 years old. Participants reported an average of three to five bowel movements each week, a frequency the researchers classified as mild constipation.

Participants were randomly assigned to drink either a vinegar beverage or a placebo beverage with breakfast each day for four weeks. The vinegar drink combined brewed vinegar with water and delivered 750 milligrams of acetic acid in a serving measuring 200 milliliters.

The placebo contained a small amount of citric acid instead of vinegar, giving it a similarly tart flavor so participants could not identify their assigned drink. Both beverages were sweetened with sucralose and flavored with apple.

During the first week, the vinegar group showed trends toward improvement in bowel movement frequency, the number of days with defecation and stool volume compared with the placebo group. By the fourth week, bowel movement frequency was significantly higher among participants receiving vinegar.

The difference amounted to about 1.2 additional bowel movements per week, according to the study. The researchers wrote, “These findings suggest that daily consumption of vinegar beverages may improve defecation status in healthy adults with mild constipation, supporting a potential dietary approach for maintaining bowel health.”

Both groups gradually improved during the study. Researchers suggested that some participants might have been habitually underhydrated, meaning the added daily beverage could have contributed to constipation relief regardless of whether it contained vinegar.

Still, the vinegar group showed greater signs of improvement during the first week. Researchers said this pattern suggested that vinegar or acetic acid might have provided an additional early benefit.

Jamie Lee McIntyre, a Florida based registered dietitian who was not involved in the research, called the study “a promising clue rather than proof that vinegar treats constipation.” She also emphasized that researchers tested a standardized beverage containing a specific quantity of acetic acid, not concentrated vinegar shots or typical apple cider vinegar supplements.

“I wouldn’t leap from this study to recommending apple cider vinegar shots for constipation,” McIntyre said. She recommended relying on strategies with stronger supporting evidence, including adequate fiber and fluids, regular physical activity and a consistent bathroom routine.

McIntyre said vinegar can be included in meals or used as the base for sauces and dressings. However, she added, “I wouldn't consider it a constipation treatment based on this one small study.”

Dr. Eric Shah, a gastroenterologist and clinical associate professor at the University of Michigan, said simply drinking more water does not necessarily relieve constipation. He said adequate hydration, soluble fiber and pelvic floor physical therapy when needed are important considerations.

Shah said trials involving mineral rich water, particularly water rich in magnesium, have shown more benefit for constipation. He said the mineral content is probably more important than the amount of fluid consumed for most people.

McIntyre also warned that consuming more vinegar does not necessarily produce better results. “Because vinegar is highly acidic, drinking it regularly — particularly undiluted — can irritate the esophagus and contribute to dental enamel erosion,” she said.

The research was funded by Mizkan Holdings Co. Ltd., a Japanese food company that manufactures vinegar, and three researchers were employed by Mizkan. The scientists said the results should be considered preliminary and confirmed through additional studies.