Lactose malabsorption in the elderly: role of small intestinal bacterial overgrowth.
OBJECTIVE
The prevalence of lactose malabsorption (LM) is increased in the elderly, although the mechanisms responsible are still a matter of speculation. The objective of this study was to investigate the possible roles of reduced functional small intestinal absorptive area, lactase deficiency and small intestinal bacterial overgrowth (SIBO).


METHODS
Twenty Caucasian (Anglo-Celtic), asymptomatic, well-nourished, elderly volunteers (median age 79 years, range 70-94 years) with no clinically apparent predisposition to SIBO underwent a 50 g lactose breath hydrogen test (LBHT) and mannitol absorption test, the latter as an index of functional small intestinal absorptive area. Those with LM additionally underwent bacteriological assessment of small intestinal secretions and mucosal biopsy, to assess the contribution of SIBO and lactase deficiency, respectively, to the pathogenesis of LM in individual cases. The prevalence of SIBO was also determined in elderly subjects without LM. Twenty asymptomatic younger subjects (median age 29 years, age range 18-35 years) served as controls. All subjects were "hydrogen producers" in response to lactulose.


RESULTS
LM was evident in 10/20 (50%) elderly subjects and 1/20 (5%) younger subjects (p=0.003). Mannitol absorption did not differ significantly in elderly and younger subjects or in elderly subjects with and without LM. SIBO was documented in 9/10 (90%) elderly subjects with LM; eradication was associated with resolution of LM. Lactase deficiency was evident in only one elderly subject with LM. SIBO was evident in 2/10 (20%) elderly subjects without LM (p=0.005 compared to those with LM). Lactulose breath hydrogen test identified only 2/11 (18%) elderly subjects with SIBO.


CONCLUSIONS
Increased prevalence of LM in the elderly is mostly due to clinically non-apparent SIBO, rather than mucosal factors. The lactulose breath hydrogen test cannot be relied upon to identify elderly subjects with SIBO, even in those without an anatomical predisposition.
Almeida
John A
JA
Gastrointestinal and Liver Unit, The Prince of Wales Hospital and University of New South Wales, Sydney, Australia.
Kim
Robert
R
Stoita
Alina
A
McIver
Christopher J
CJ
Kurtovic
Jelica
J
Riordan
Stephen M
SM
D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001944:Breath Tests; D005260:Female; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism / Q000382:microbiology; D007421:Intestine, Small / Q000378:metabolism / Q000382:microbiology*; D043322:Lactase / Q000172:deficiency; D007785:Lactose / Q000493:pharmacokinetics; D007792:Lactulose; D008286:Malabsorption Syndromes / Q000175:diagnosis / Q000453:epidemiology / Q000378:metabolism* / Q000382:microbiology*; D008297:Male; D008353:Mannitol / Q000493:pharmacokinetics; D015995:Prevalence; D015203:Reproducibility of Results
D008353:Mannitol; D007792:Lactulose; D006859:Hydrogen; D043322:Lactase; D007785:Lactose