Comparative tolerance of adolescents of differing ethnic backgrounds to lactose-containing and lactose-free dairy drinks. II. Improvement of a double-blind test.

Using an improved double-blind test procedure, the relationship between lactose malabsorption and lactose intolerance was investigated in 87 healthy teenagers (14--19 years old) of differing ethnic backgrounds. Capillary blood glucose analysis after an oral dose of 50 g of lactose identified 45 lactose malabsorbers. A lactose-free (LF) chocolate dairy drink and one containing 4.5% lactose (LC) were administered under double-blind conditions on 4 consecutive mornings. As in a similar prior study, no statistically significant differences were found in the incidence of symptoms reported by malabsorbers and absorbers after drinking 240 ml of either the LF or the LC preparation. However, 12 lactose absorbers reported symptoms apparently not due to lactose, i.e., after 240 ml of LF, after this amount of both LF and LC, or after 240 ml (but not 480 ml) of LC. Such false-positive results would only be identified by the double-blind approach. It did not appear that any of the malabsorbers had symptoms due to the lactose in 240 ml of LC. However, 16% of the malabsorbers apparently reacted to the lactose in 480 ml of LC. Well designed, double-blind clinical trials are essential for evaluation of gastrointestinal responses to lactose or other ingredients in milk.