Prevalence of lactose intolerance in Chile: a double-blind placebo study.

BACKGROUND AND STUDY AIMS: Lactase non-persistence (LNP), or primary hypolactasia, is a genetic condition that mediates lactose malabsorption and can cause lactose intolerance. Here we report the prevalence of lactose intolerance in a double-blind placebo study. METHODS: The LCT C>T-13910 variant was genotyped by RT-PCR in 121 volunteers and lactose malabsorption was assessed using the hydrogen breath test (HBT) after consuming 25 g of lactose. Lactose intolerance was assessed by scoring symptoms (SS) using a standardized questionnaire following challenge with a lactose solution or saccharose placebo. RESULTS: The LNP genotype was observed in 57% of the volunteers, among whom 87% were HBT⁺. In the HBT⁺ group the median SS was 9 and in the HBT⁻ group the median SS was 3 (p < 0.001). No difference was observed in the SS when both groups were challenged with the placebo. The most common symptoms included audible bowel sounds, abdominal pain and meteorism. In the ROC curve analysis, an SS ≥ 6 demonstrated 72% sensitivity and 81% specificity for predicting a positive HBT. To estimate prevalence, lactose intolerance was defined as the presence of an SS ≥ 6 points after subtracting the placebo effect and 34% of the study population met this definition. CONCLUSIONS: The LNP genotype was present in more than half of subjects evaluated and the observed prevalence of lactose intolerance was 34%.

Red cell membrane lipid changes at 3,500 m and on return to sea level.

Previous studies have shown that acute hypobaric hypoxia, obtained in a hypobaric chamber, and subsequent reoxygenation, give rise to modifications of the erythrocyte membrane lipid dynamics, resulting in an increased lateral diffusivity of the membrane lipids, and this was interpreted as the result of a modified lipid-protein interaction. The aim of the present study was to determine the effect of the reoxygenation condition in individuals after 3 days at an altitude of 3,500 m above sea level. Reoxygenation was a consequence of returning to sea level. Resting blood samples from both conditions were obtained, and erythrocytes were separated and immediately lysed for membrane isolation. We measured the bilayer polarity in membranes with Laurdan, a fluorescent probe. We also measured malondialdehyde in membrane lipids, an indicator of oxidative damage. We found a 12% (p = 0.016, n = 7) increase in the polarity of the membrane bilayer surface, and an increase of 70% (p = 0.005, n = 7) in the formation of malondialdehyde in the membrane after the reoxygenation condition. The membrane bilayer polarity increase is due to an oxidative modification of the phospholipid backbone after reoxygenation. People working and/or recreating at moderate altitude (3,500 m) may be at risk of erythrocyte membrane oxidative damage upon returning to sea level, and therefore a better understanding of the processes occurring upon reoxygenation may lead to proposed strategies to minimize this effect.

Hypobaric hypoxia-reoxygenation diminishes band 3 protein functions in human erythrocytes.

We have previously shown that subjects exposed to acute hypobaric hypoxia display an erythrocyte membrane protein band 3 with an increased susceptibility to proteolytic degradation. We suggested it was due to an oxidative damage of band 3. We now report that exposure to hypobaric hypoxia followed by reoxygenation affects protein band 3 functions such as anion transport and binding of glyceraldehyde-3P-dehydrogenase. Transport capacity was assessed with the fluorescent probe 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino] ethanesulfonate (NBD-taurine). Binding capacity was evaluated from the activity of the membrane-associated enzyme. Healthy young men were exposed for 20 min to hypobaric hypoxia, simulating an altitude of 4,500 m above sea level and after recompression band 3 function was assessed. An inhibition of band 3 anion transport function and a decrease in the binding of glyceraldehyde-3P-dehydrogenase to band 3 were observed. Evidence is given supporting the hypothesis that functional alteration of band 3 is due to its oxidative modification originated as a consequence of the exposure to hypobaric hypoxia and further reoxygenation.