lactase

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lactase The enzyme that metabolizes lactose. It is present in the stomach of neonatal mammals, but usually ceases to be secreted after weaning, hence milk is indigestible to most mammalian species after this time. In humans, it is a polymorphism: lactase is secreted throughout life in most people of north European and north Indian origin, but its frequency declines towards the tropics and most tropical, East Asian, Australian Aboriginal, Pacific, and Native American peoples cannot digest milk.

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