Lactose Intolerance
Lactose intolerance is a biochemical condition caused by the inability to digest fully the sugar in milk, i.e., lactose [1]. The condition of lactose intolerance is better described as “lactose sensitivity,” as everyone can tolerate some lactose, although
- PDF / 245,489 Bytes
- 6 Pages / 504.57 x 720 pts Page_size
- 95 Downloads / 214 Views
Introduction to Lactose Intolerance Lactose intolerance is a biochemical condition caused by the inability to digest fully the sugar in milk, i.e., lactose [1]. The condition of lactose intolerance is better described as “lactose sensitivity,” as everyone can tolerate some lactose, although this amount varies considerably between individuals [2]. It is essential to distinguish lactose intolerance from an allergy to milk proteins as there are major differences in the management of these two conditions and allergy occurs in 3–5 % of infants. Some four billion people around the world express low lactase levels (see below) and are thus potentially sensitive to lactose, suffering a range of gut and systemic symptoms (Fig. 1), unless diagnosed and then managed correctly. Lactose sensitivity is associated with two common gut conditions [3], irritable bowel syndrome (IBS, a disease characterized by abdominal pain, diarrhea, or constipation or both alternating) and inflammatory bowel disease (IBD, a group of inflammatory conditions affecting small intestine and colon, including Crohn’s
A.K. Campbell (*) School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Redwood Building, King Edward VII Avenue, Cardiff CB10 3NB, UK e-mail: [email protected] S.B. Matthews Welston Court Science Centre, Milton, Pembrokeshire SA70 8PS, UK e-mail: [email protected]
disease and ulcerative colitis) [4], and thus should be taken into account when diagnosing and treating these patients [5]. Lactose, galactose-1,4-β-glucose, is only found naturally in significant amounts in mammalian milk (cow’s milk 49 g/l; human milk 70 g/l). Lactose is one sixth as sweet as sucrose and provides some 40 % of the energy requirements of a suckling infant. However, adults do not need lactose. Disaccharides (e.g., lactose, sucrose, and isomaltose) cannot be absorbed directly in the intestine, requiring an enzyme to cleave them into monosaccharides. Lactose is cleaved by lactase (lactase-phlorizin hydrolase), which occurs in the small intestinal microvilli. Galactose and glucose are subsequently absorbed into the enterocyte via the sodium-activated glucose transporter 1 (SGLUT1, also called SGLT1). Glucose and galactose are then taken up into the blood by the transporter GLUT2. Galactose is converted to glucose mainly by the Leloir pathway, where galactose is converted to UDP-glucose, particularly in the liver via galactose 1-phosphate (Gal-1-P) and UDP-galactose. Alternatively, humans can use the De Ley-Doudoroff pathway. Inherited mutations of enzymes in the Leloir pathway cause galactosemias, affecting 1 in 55,000 individuals. For example, galactosemia type 1 (galactose-1-phosphate uridylyltransferase deficiency) is seen in suckling infants causing severe illness, including not wanting to drink, vomiting, jaundice, hypoglycemia, enlarged liver (hepatomegaly), enlarged spleen (splenomegaly), proximal tubulus kidney damage, cataract, mental retardation, and failure to thrive.
E. Lammert, M. Zeeb (eds.), Metabolism of Human Diseases, DOI 10.
Data Loading...
