Lactose consumption has been associated with a high incidence of
cataract in northern Indian and southern Italian populations.
Galactose absorbed after hydrolysis of
lactose from milk in individuals with normal
lactase activity is considered responsible. However,
lactase-deficient subjects who often avoid drinking milk are able to digest
lactose and absorb free
galactose in fermented milk and yogurt. This study was conducted to evaluate the relationships between milk and yogurt consumption,
galactose metabolism and
cataract risk. Milk ingestion was dose-related with
cataract risk in
lactose digesters (particularly in diabetics) but not in
lactose maldigesters. Conversely, yogurt intake had a protective dose-effect on
cataract formation for the whole population. Maximal
galactose concentrations after an oral
galactose test increased exponentially with age. Red blood cell
galactokinase activity was significantly lower in elderly subjects (> 60 y) than in young individuals (P < 0.05), and
galactose-1-phosphate uridyl-transferase activity was significantly lower in institutionalized subjects and in home-living elderly with
cataract than in healthy elderly subjects (P < 0.05). We conclude that the cataractogenic action of milk
lactose is dependent on the disturbance of
galactose metabolism in elderly subjects and that yogurt is not cataractogenic, although the mechanism of the protective effect of yogurt remains unknown.