A daily vinegar drink helped adults with mild constipation manage 1.2 more bowel movements a week within a month, a Japanese trial has found, but a vinegar maker paid for the research.

Gains in bowel frequency and stool volume appeared within the first week. Experts call the result promising but far from conclusive, and no substitute for proven remedies.

The National Institutes of Health says constipation generally means fewer than three bowel movements a week. Stools may also be hard, dry or lumpy, making them difficult or painful to pass.

Left untreated, chronic constipation can lead to haemorrhoids and anal fissures. In severe cases, it may cause faecal impaction, a complication that can require emergency care.

Vinegar Drink Trial

The study, published in Scientific Reports, examined whether a vinegar beverage could ease mild constipation. Acetic acid, vinegar's main active component, may drive the effect, the team wrote.

Researchers randomly assigned 44 healthy Japanese adults, aged 20 to 69, to a vinegar drink or a placebo at breakfast for four weeks. All began with three to five bowel movements a week.

The drink contained 750 milligrams of acetic acid per 200-millilitre serving, mixed with water. The placebo used citric acid to achieve a similar tart taste and was sweetened the same way.

By week four, the vinegar group averaged 1.2 more bowel movements a week than the placebo group. Both groups improved over time, possibly because some participants began mildly dehydrated.

The researchers wrote that daily vinegar may improve defecation in adults with mild constipation.

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How Vinegar May Help

Most swallowed acetic acid is absorbed before reaching the colon, earlier research found. Even so, its authors suggested any acid that arrives there may trigger serotonin release that stimulates gut movement.

The trial built on an earlier study of more than 1,000 adults, which linked eating vinegar-based dishes, such as sunomono, to more frequent bowel movements. That cross-sectional research prompted the new controlled trial.

Separate animal research on Shanxi aged vinegar found it reshaped gut bacteria and reduced inflammation in mice. Its authors said the changes may help explain vinegar's wider health benefits.

Specialists Urge Caution

Florida dietitian Jamie Lee McIntyre, who was not involved, called the findings promising but far from conclusive. She noted the study used a controlled beverage, not apple cider vinegar shots.

The trial was funded by Mizkan Holdings, a Japanese vinegar maker, and three researchers were company employees. The scientists called the findings preliminary and said more research is needed.

McIntyre said proven strategies still include adequate fibre, fluids, exercise and a consistent bathroom routine. Vinegar can complement a meal, she added, but is not a stand-alone treatment.

The NIH recommends 22 to 34 grams of fibre a day, yet fewer than 10 per cent of women and about three per cent of men meet that target. It advises legumes, whole grains, fruit, vegetables, nuts and seeds first.

Over-the-counter medicines can help when lifestyle changes fall short, the NIH says.

Dr Eric Shah, a University of Michigan gastroenterologist, said drinking more water alone is a common misconception. Mineral-rich water, especially with magnesium, tends to help more than volume alone.

Shah said hydration, soluble fibre and pelvic floor therapy can help, adding that pelvic floor therapy is a growing field available through primary care.

McIntyre cautioned that more vinegar is not necessarily better. Because it is highly acidic, drinking it often, particularly undiluted, can irritate the oesophagus and erode tooth enamel.

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