Background The prevalence of generically determined lactase nonpersistence
is based on the results of the lactose H-2 breath rest. This test, however,
is an indirect test, which might lead to misinterpretation.
Design We determined lactase activity in healthy Chinese and Dutch students
using a novel C-13-lactose digestion test. The cut-off value of this rest
was established in a Chinese population with a homogenous genetic backgroun
d of lactase nonpersistence and was compared with the results obtained in a
Caucasian population Twenty-five grams of a C-13-lactose solution was cons
umed by 12 known H-2-positive and 5 H-2-negative Chinese students and 48 Du
tch students and, subsequently, C-13-glucosc concentration in plasma and H-
2 excretion in breath were measured.
Results A similar C-13-glucose response curve was round in all Chinese stud
ents. The mean response curve in the Dutch students was more pronounced (P
< 0.01). The 1 h (peak) plasma C-13-glucose concentration was the best disc
riminator between lactose digesting and maldigesting subjects. The cut-off
level of 2 mmol L-1 C-13-glucose in plasma was defined in the H-2-positive
Chinese students group. Based on the C-13-glucose response the prevalence o
f lactose maldigestion in the Dutch subjects was 25%; based on the lactose
H-2 breath test 17%.
Conclusions Using the C-13-lactose digestion test the results demonstrate a
higher prevalence of lactose maldigestion in a Caucasian population than i
ndicated by the results of the H-2 breath test. A moderate increase in the
plasma C-13-glucose concentration after consumption of C-13-lactose in the
young adult Chinese subjects indicates a residual lactase activity in that
age group, even when a positive H-2 breath test result is obtained. These r
esults indicate that the C-13-glucose concentration in plasma more accurate
ly reflects the small intestinal lactose digestion capacity than the lactos
e H-2 breath test.