The Subjective Perception of Lactose Intolerance
Background Symptoms of lactose intolerance are often attributed to lactose malabsorption but, as this relationship has not been demonstrated when a small dose of lactose similar to that contained in one cup of milk is ingested by intolerant patients, psychological factors may play a role in altered symptom perception.
Aim To assess the hypothesis that the psychological profile influences the symptoms of lactose intolerance.
Methods One hundred and two consecutive patients underwent a 15 g lactose hydrogen breath test to assess lactose malabsorption. The patients recorded the presence and severity of symptoms of lactose intolerance during the breath test using visual analogue scales. The psychological profile was assessed using a psychological symptom checklist, and health-related quality of life by means of the short-form health survey.
Results Lactose malabsorption and intolerance were diagnosed in, respectively, 18% and 29% of the patients. The two conditions were not associated, and the severity of intolerance was even less in the patients with malabsorption. Multivariate logistic analysis showed that a high somatisation t-score was significantly associated with lactose intolerance (odds ratio 4.184; 1.704–10.309); the effects of the other psychological variables and of lactose malabsorption were not statistically significant. Health-related quality of life was significantly reduced in the patients with somatisation, but not in those with lactose malabsorption.
Conclusions The symptoms of lactose intolerance during hydrogen breath testing at a low physiological lactose load, are unrelated to lactose malabsorption, but may reveal a tendency towards somatisation that could impair the quality of life.
Sensations such as abdominal pain and bloating, flatulence and diarrhoea are often attributed by patients to the ingestion of milk or milk derivatives containing even small quantities of lactose, and this makes them lactose intolerant. One of the mechanisms thought to be involved in the pathogenesis of lactose intolerance is lactose malabsorption: i.e. the nonpersistence of intestinal lactase on the brush border that prevents the small bowel from hydrolysing and absorbing sugar, and subsequently gives rise to the fermentation of malabsorbed lactose by colonic bacteria. Some physicians believe that the relationship between lactose malabsorption and lactose intolerance is so strong that the two terms can be used interchangeably, and that the wide range of gut and systemic symptoms reported by patients with lactose intolerance may be due to toxic metabolites of the malabsorbed lactose.
These beliefs arise from observations that the ingestion of large doses of lactose (such as the 50 g contained in one litre of milk) induce abdominal pain, nausea, diarrhoea, bloating and flatulence in subjects with lactose malabsorption. However, other factors seem to be involved in reports of symptoms after the ingestion of large doses of lactose. Casellas et al. have recently observed that the severity of the gastrointestinal symptoms that patients attribute to lactose intolerance in everyday life exceeds the intensity of those caused by the administration of 50 g of lactose under controlled laboratory conditions, and do not depend on the presence of lactose absorption or malabsorption. This suggests that patients with lactose intolerance tend to have an exaggerated recall of their symptoms, and that the perception of the symptoms may be unrelated to lactose malabsorption.
The relationship between the symptoms of lactose intolerance and lactose malabsorption is even weaker when smaller physiological doses of lactose are ingested. In the seminal double-blind study of Suarez et al., a self-selected group of people who identified themselves as severely lactose-intolerant ingested 240 g of milk (15 g of lactose) or an equivalent dose of lactose-hydrolysed milk: their symptoms were minimal and not significantly different. The discrepancy between the patients' conception that ingesting small quantities of milk causes severe gastrointestinal symptoms and the fact that the same patients reported only trivial symptoms after ingesting milk under controlled conditions suggests that psychological factors may play a role in the perception and reporting of symptoms of lactose intolerance. This hypothesis has been previously investigated by Suarez et al., but the results were inconclusive, possibly because of the small sample size and the high rate of invalid evaluations of psychological factors.
The aim of this study was to explore the same hypothesis by assessing whether the symptoms of lactose intolerance after the ingestion of 15 g of lactose are due to lactose malabsorption or an altered psychological profile in a large series of consecutive patients with suspected lactose malabsorption.
Abstract and Introduction
Abstract
Background Symptoms of lactose intolerance are often attributed to lactose malabsorption but, as this relationship has not been demonstrated when a small dose of lactose similar to that contained in one cup of milk is ingested by intolerant patients, psychological factors may play a role in altered symptom perception.
Aim To assess the hypothesis that the psychological profile influences the symptoms of lactose intolerance.
Methods One hundred and two consecutive patients underwent a 15 g lactose hydrogen breath test to assess lactose malabsorption. The patients recorded the presence and severity of symptoms of lactose intolerance during the breath test using visual analogue scales. The psychological profile was assessed using a psychological symptom checklist, and health-related quality of life by means of the short-form health survey.
Results Lactose malabsorption and intolerance were diagnosed in, respectively, 18% and 29% of the patients. The two conditions were not associated, and the severity of intolerance was even less in the patients with malabsorption. Multivariate logistic analysis showed that a high somatisation t-score was significantly associated with lactose intolerance (odds ratio 4.184; 1.704–10.309); the effects of the other psychological variables and of lactose malabsorption were not statistically significant. Health-related quality of life was significantly reduced in the patients with somatisation, but not in those with lactose malabsorption.
Conclusions The symptoms of lactose intolerance during hydrogen breath testing at a low physiological lactose load, are unrelated to lactose malabsorption, but may reveal a tendency towards somatisation that could impair the quality of life.
Introduction
Sensations such as abdominal pain and bloating, flatulence and diarrhoea are often attributed by patients to the ingestion of milk or milk derivatives containing even small quantities of lactose, and this makes them lactose intolerant. One of the mechanisms thought to be involved in the pathogenesis of lactose intolerance is lactose malabsorption: i.e. the nonpersistence of intestinal lactase on the brush border that prevents the small bowel from hydrolysing and absorbing sugar, and subsequently gives rise to the fermentation of malabsorbed lactose by colonic bacteria. Some physicians believe that the relationship between lactose malabsorption and lactose intolerance is so strong that the two terms can be used interchangeably, and that the wide range of gut and systemic symptoms reported by patients with lactose intolerance may be due to toxic metabolites of the malabsorbed lactose.
These beliefs arise from observations that the ingestion of large doses of lactose (such as the 50 g contained in one litre of milk) induce abdominal pain, nausea, diarrhoea, bloating and flatulence in subjects with lactose malabsorption. However, other factors seem to be involved in reports of symptoms after the ingestion of large doses of lactose. Casellas et al. have recently observed that the severity of the gastrointestinal symptoms that patients attribute to lactose intolerance in everyday life exceeds the intensity of those caused by the administration of 50 g of lactose under controlled laboratory conditions, and do not depend on the presence of lactose absorption or malabsorption. This suggests that patients with lactose intolerance tend to have an exaggerated recall of their symptoms, and that the perception of the symptoms may be unrelated to lactose malabsorption.
The relationship between the symptoms of lactose intolerance and lactose malabsorption is even weaker when smaller physiological doses of lactose are ingested. In the seminal double-blind study of Suarez et al., a self-selected group of people who identified themselves as severely lactose-intolerant ingested 240 g of milk (15 g of lactose) or an equivalent dose of lactose-hydrolysed milk: their symptoms were minimal and not significantly different. The discrepancy between the patients' conception that ingesting small quantities of milk causes severe gastrointestinal symptoms and the fact that the same patients reported only trivial symptoms after ingesting milk under controlled conditions suggests that psychological factors may play a role in the perception and reporting of symptoms of lactose intolerance. This hypothesis has been previously investigated by Suarez et al., but the results were inconclusive, possibly because of the small sample size and the high rate of invalid evaluations of psychological factors.
The aim of this study was to explore the same hypothesis by assessing whether the symptoms of lactose intolerance after the ingestion of 15 g of lactose are due to lactose malabsorption or an altered psychological profile in a large series of consecutive patients with suspected lactose malabsorption.
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