High frequency of lactase activity deficiency in small bowel of adults in the Neapolitan area

Lactose malabsorption and intolerance in Italians. Clinical implications

Lactose malabsorption was assessed by the hydrogen breath test in 40 Italian patients with irritable bowel syndrome and 42 controls without abdominal disturbances. Sixty-five percent of patients were "low milk consumers" (0-250 ml milk per day) compared with 38% of controls (P less than 0.02). Lactose loads of 25 and 50 g caused malabsorption in 82.5 and 87.5% patients and in 55 and 62% controls, respectively (patients vs controls P less than 0.02). Malabsorption was more frequent in the "low milk consumers" group (P less than 0.05). During a four-month lactose-free diet as the only treatment 7.5% of patients became symptom-free (and remained so for a further eight-month diet), 52.5% improved, and 40% showed no change.

High frequency of lactose absorbers among adults with idiopathic senile and presenile cataract in a population with a high prevalence of primary adult lactose malabsorption

22% of a group of adult Neapolitans were found to have persistent high lactase activity, and 16% were lactose absorbers as indicated by measurement of breath hydrogen concentration and rise in blood glucose after oral lactose administration. Among adults in the same area with idiopathic senile or presenile cataract 49% were identified as lactose absorbers with the breath hydrogen test and 55% by the rise in blood glucose. These results suggest that adults able to absorb galactose from a lactose-containing diet are especially susceptible to senile or presenile cataract.

Respiratory excretion of hydrogen and methane in Italian subjects after ingestion of lactose and milk

Lactose malabsorption, by the breath hydrogen test, and lactose intolerance (presence of symptoms) were studied in twenty healthy Italian subjects after intake of 12.5, 25 and 50 g lactose, whole milk and low-lactose milk. A rise in respiratory concentration of hydrogen (greater than 20 ppm) (malabsorption) was found in fifteen subjects after 50 g lactose, in thirteen after 25 g and in seven after 12.5 g. Symptoms generally occurred in subjects presenting a rise in respiratory hydrogen excretion, but such a rise was often observed without symptoms. Thirteen subjects presented symptoms after 50 g lactose, but only three after 25 g and one after 12.5 g. Whole milk (500 ml) gave a lower incidence of lactose malabsorption than 25 g lactose (7/20 versus 13/20, P less than 0.05) and more subjects developed symptoms (7/20 versus 3/20, NS). Low-lactose milk produced no malabsorbers and one intolerant. Breath methane was detected constantly in seven subjects and in three on some of the days of observation. Respiratory methane excretion generally appeared to be unrelated to lactose ingestion.

The geographic hypothesis and lactose malabsorption. A weighing of the evidence

Reviewed in this article is evidence bearing on the geographic hypothesis advanced eight years ago to explain the striking ethnic or racial differences in prevalence of primary adult lactose malabsorption that are found around the world. Most evidence is found to support the hypothesis and the likelihood that some human groups came to have low prevalences of such lactose malabsorption because of selective pressures over a long historical period that favored the adult lactose absorber under particular ecological conditions.