title: Lactose intolerance: analysis of underlying factors.
abstract: BACKGROUND
  We studied the degree of lactose digestion and orocecal transit time (OCTT) as possible causes for the variability of symptoms of lactose intolerance (LI) in a sample of a population with genetically determined low lactase activity.
  
  
  METHODS
  Lactose digestion index (LDI) was measured by the recently developed 13C-lactose/2H-glucose test. The OCTT was determined using the breath hydrogen test. Based on a 6-h symptom score (SSC) after a challenge dose of 25 g of lactose the subjects were divided into a tolerant group (T: n= 15; SSC = 0) and an intolerant group (IT: n= 28; SSC 1-40). The intolerant group was subdivided according to the severity of symptoms: group ITa (n = 17; mild symptoms without diarrhoea) and group ITb (n = 11; with diarrhoea).
  
  
  RESULTS
  The LDI was lower in the intolerant group (0.34 +/- 0.14) (mean +/- SD) than in the tolerant group (0.47 +/- 0.14) (P = 0.008). The OCTT of group IT (60, 30-90 min) (median, quartiles) was significantly shorter than that of group T (105, 60-120 min) (P = 0.003) and was positively correlated with the LDI (P = 0.050). In groups ITa and ITb the OCTT (60, 30-90 min; 60, 26-83 min) and LDI (0.30 +/- 0.14; 0.39 +/- 0.14) were similar.
  
  
  CONCLUSIONS
  Lactose digestion capacity, which is determined by small intestinal lactase activity as well as by OCTT, affects the occurrence of lactose intolerance. However, the major difference in intolerance symptoms is caused by differences in the colonic processing of maldigested lactose.
authors.affiliation: Laboratory Nutrition and Metabolism, Laboratory Centre CMC V, Y2147, University Hospital Groningen, PO Box 30 001, 9700 Groningen, the Netherlands. r.j.vonk@med.rug.nl
authors.forename: R J
authors.initials: RJ
authors.lastname: Vonk
authors.forename: M G
authors.initials: MG
authors.lastname: Priebe
authors.forename: H A
authors.initials: HA
authors.lastname: Koetse
authors.forename: F
authors.initials: F
authors.lastname: Stellaard
authors.forename: I
authors.initials: I
authors.lastname: Lenoir-Wijnkoop
authors.forename: J-M
authors.initials: JM
authors.lastname: Antoine
authors.forename: Y
authors.initials: Y
authors.lastname: Zhong
authors.forename: C-Y
authors.initials: CY
authors.lastname: Huang
mesh_terms: D000328:Adult; D000367:Age Factors; D001944:Breath Tests; D002247:Carbon Isotopes; D003967:Diarrhea / Q000503:physiopathology; D004063:Digestion; D005260:Female; D005772:Gastrointestinal Transit; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D007421:Intestine, Small / Q000201:enzymology; D043322:Lactase; D007787:Lactose Intolerance / Q000503:physiopathology*; D007789:Lactose Tolerance Test; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D006859:Hydrogen; D043322:Lactase; D001616:beta-Galactosidase