Lactose (mal)digestion evaluated by the C-13-lactose digestion test

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 background of lactase nonpersistence and was compared with the results obtained in a Caucasian population Twenty-five grams of a C-13-lactose solution was consumed by 12 known H-2-positive and 5 H-2-negative Chinese students and 48 Dutch 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 students. 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 discriminator 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 of 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 indicated 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 results indicate that the C-13-glucose concentration in plasma more accurately reflects the small intestinal lactose digestion capacity than the lactose H-2 breath test.