Relationships of Intestinal Lactase and the Small Intestinal Microbiome with Symptoms of Lactose Intolerance and Intake in Adults

Abstract

Background: Approximately two-thirds of adults are genetically predisposed to decreased lactase activity after weaning, putting them at risk of lactose intolerance. However, symptoms are a poor marker of lactose maldigestion.

Aims: We assessed association between self-reported lactose intolerance and intestinal lactase, lactose intake, and the small intestinal microbiome.

Methods: Patients 18-75 years presenting for upper endoscopy were recruited prospectively. Observational study participants completed a lactose intolerance symptom questionnaire and reported lactose intake. Post-bulbar biopsies were obtained to measure lactase activity and assess the small intestinal mucosal microbiome. We compared intestinal lactase between patients with and without lactose intolerance. We assessed associations between lactose intolerance symptoms and lactase and lactose intake. We examined associations of small bowel microbial composition with self-reported lactose intolerance and symptoms.

Results: Among 34 patients, 23 (68%) reported lactose intolerance. Those with lactose intolerance had higher total symptom scores, more frequent bowel urgency, and more bowel movements after consuming dairy. The proportion of individuals with abnormal lactase activity did not differ by lactose intolerance status. Median lactase levels were correlated with total lactose intolerance symptom scores (p = 0.038) and frequency of bowel urgency (p = 0.012). Daily lactose intake did not differ between groups. In 19 patients, we observed significant associations of small intestinal microbiome beta diversity with stool consistency after consuming dairy (p = 0.03).

Conclusions: Intestinal lactase is associated with lactose intolerance symptoms and bowel urgency in adults but does not distinguish the clinical phenotype entirely. Studying other contributing factors (microbiota, diet) may further clarify the pathophysiology of lactose intolerance.

Keywords: Disaccharide; Duodenum; Food intolerance; Maldigestion; Small intestine.

Figure 1.

Flow Chart of Study Participants

Figure 2.

Boxplots of disaccharidase levels by self-reported lactose intolerance °There were 2 notable outliers for lactase level, one for each group.

Figure 3.

Scatter plot of lactase level against symptom severity with Spearman correlation

Figure 4.

Scatter plot of average daily lactose intake (grams) against symptom severity Note that one subject had an average lactose intake of approximately 160 grams per day and was excluded from Figure 4 as an extreme outlier.

Figure 5.

Assessment of Small Intestine Mucosa-Associated Beta Diversity

Figure 6.

Assessment of Small Intestine Mucosa-Associated Alpha Diversity