Postmenopausal Women with IBS-C Benefit from Melatonin More than IBS-D Counterparts

Recognizing that melatonin secretion from the gastrointestinal (GI) tract improves abdominal pain in irritable bowel syndrome (IBS) but decreases with age, Polish researchers from the Medical University of Lodz aimed to define the effect of administering melatonin in postmenopausal women with different predominating IBS symptoms.

For their “Influence of Melatonin on Symptoms of Irritable Bowel Syndrome in Postmenopausal Women” study published in Volume 64 of Endokrynologia Polska in 2013, Cezary Chojnacki, MD, and colleagues at the university’s gastroenterology and neuroendocrinology departments enrolled 80 postmenopausal women between the ages of 48 and 65 with constipation-predominant IBS (IBS-C) or diarrhea-predominant IBS (IBS-D), as well as a control group of 30 postmenopausal women between the ages of 31 and 45 without GI disorders or complaints.

After withdrawing current medications from each participant and then collecting urine samples to record initial urinary 6-sulfatoxymelatonin (6-HMS) levels, 20 patients from each of the IBS groups received a 3-milligram morning dose and 5-milligram evening dose of melatonin for six months, while the remaining 40 patients between those two groups received placebo in the same regimen and for the same length of time. Throughout the six-month period, patients also maintained an observation diary concerning the intensity of visceral pain, abdominal bloating, and constipation or diarrhea.

At the conclusion of the study, the researchers found no significant difference in mean urinary 6-HMS secretion between the IBS-C patients and the healthy subjects, but they noted that mean hormone secretion was much higher in the IBS-D patients than those in the control group. However, the investigators noted that the nine-week melatonin regimen didn’t significantly alter symptoms in the IBS-D group compared to the placebo group, though they found that in the IBS-C group, “melatonin decreased IBS symptoms more distinctly compared to placebo … (and) these differences were statistically significant when evaluated in the four and six months of melatonin administration.”

Those distinct differences in the IBS-C patients who received melatonin included improvement in bowel movement in nine of the 20 patients in that group, total regression of abdominal pain in 12 of those patients, and a decrease in abdominal bloating in 14 of those patients, according to the researchers.

“The results of the treatment were more beneficial in IBS-C patients; thus, it can be supposed that the beneficial effect was associated with melatonin’s relaxative properties on the smooth muscles of the gut, which in consequence led to diminished abdominal distension,” the authors concluded.

Though their study results broadly supported twice-daily melatonin in combination IBS treatment — particularly for IBS-C patients — the authors more narrowly noted that “patients with IBS have disturbances of the gastrointestinal tract (abdominal pain, bloating, diarrhea) during the day, but never at night. For this reason, a fasting dose of melatonin may have a beneficial influence on GI function.”