Lactose is a reducing sugar consisting of galactose and glucose, linked by a β (1→4) glycosidic bond,
considered as an antioxidant due to its α-hydroxycarbonyl group. Lactose is widely ingested through the milk and
other unfermented dairy products and is considered to be one of the primary foods. On the other hand, lactose is
also considered as one of the most widely used excipients for the development of pharmaceutical formulations. In
this sense, lactose has been related to numerous drug-excipient or drug-food pharmacokinetic interactions.
Intolerance, maldigestion and malabsorption of carbohydrates are common disorders in clinical practice, with
lactose-intolerance being the most frequently diagnosed, afflicting 10% of the world’s population. Four clinical
subtypes of lactose intolerance may be distinguished, namely lactase deficiency in premature infants, congenital
lactase deficiency, adult-type hypolactasia and secondary lactase intolerance. An overview of the main uses of
lactose in human nutrition and in the pharmaceutical industry and the problems derived from this circumstance
are described in this review.