Gourt > Health > Conditions and Diseases > Digestive Disorders > Intestinal > Lactose Intolerance
Lactose intolerance is the condition in which lactase, an enzyme needed for proper metabolization of lactose (a constituent of milk and other dairy products), is not produced in adulthood. A lactose tolerance test, a hydrogen breath test, or a stool acidity test is required for a clinical diagnosis *. With lactose intolerance, the result of consuming too much lactose is excess gas production and often diarrhea. Lactose-intolerant adults can drink about 250 ml (8 oz) of milk per day without severe symptoms (McGee 2004) (Swagerty et al. 2002). Most adults in the world are lactose-intolerant: the majority of humans stop producing significant amounts of lactase sometime between the ages of two and five. A relatively recent genetic change caused some populations, including many northern Europeans, to continue producing lactase into adulthood; these lactose-tolerant populations are in the minority. Lactose intolerance is an autosomal recessive trait, while lactase-persistence is the dominant allele.
Biology
The normal mammalian condition is for the young of a species to lose the ability to digest milk sugar (lactose) effectively after the end of the weaning period (a species-specific length of time often equal to roughly 3% of lifespan). In humans, lactase production usually drops about 90% during the first four years of life, although the exact drop over time varies widely. However, certain human populations have undergone a mutation on chromosome 2 which results in a bypass of the common shutdown in lactase production, allowing members of these populations to continue consumption of fresh milk and other milk products throughout their lives.
There is some debate on exactly where and when the mutation(s) occurred, some arguing for separate mutation events in Sweden (which has one of the lowest levels of lactose intolerance in the world) and the Arabian Peninsula near 4000 BC which converged as they spread, while others argue for a single event in the Middle East at about 4500 BC which radiated from there. Some sources suggest a third and more recent mutation in the East African Tutsi. Whatever the precise origin in time and place, most modern Western Europeans and people of Western European ancestry show the effects of this mutation (that is, they are able to safely consume milk products all their lives) while most modern East Asians, sub-Saharan Africans and native peoples of the Americas and Pacific Islands do not (making them lactose intolerant as adults)*.
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Steve Carper's Lactose Intolerance Clearinghouse - Includes basics for beginners, a guide to dairy and nondairy products, a milk-free bookstore, answers to questions, online resources, and research summaries.
Meta Description: [ Everything about lactose intolerance,
including basics for beginners, a guide to dairy and to nondairy
products, a milk-free bookstore, answers to questions,
online resources, research summaries, fun stuff, and much more. ]
Dairy Free UK - Resources and information for dairy allergy and intolerance.
Meta Description: [ This is a site for the discussion of problem and products for people living with milk allergy and intolerance ]
DairyCare - A lactose intolerance dietary supplement, for management of dairy intolerance symptoms. Formulated with Acidophilus to replace the lactase enzyme to relieve lactose intolerance symptoms
Meta Description: [ DairyCare is a once daily nutritional supplement for treatment of lactose intolerance and management of lactose intolerance symptoms. Formulated with Acidophilus to replace the lactase enzyme to relieve lactose intolerance symptoms, such as bloating, abdominal cramping, and diarrhea. ]
General Practice Notebook - Lactose intolerance - Clinically-oriented information.
Kirsten's Lactose Intolerance Website - Information about the condition and its prevalence, advice and resources for living lactose-free, discussion forum, and other resources for the lactose-intolerant.
Meta Description: [ Lactose free information, resources, and other stuff for lactose intolerant people ]
Lactose Intolerance - Discussion and management of Lactose Intolerance.
Meta Description: [ Information and discussion on health issues concerning lactose intolerance, its causes, symptoms, diagnosis and treatment ]
Lactose Intolerance - Information page from the U.S. NIH National Digestive Diseases Information Clearinghouse.
Meta Description: [ Explains the mechanism involved in the inability to digest lactose, diagnostic tests, and diet modifications ]
Lactose.co.uk - About symptoms, causes, milk alternatives, dairy-free recipes, and other related topics, including Irritable Bowels Syndrome. Promotes several books on lactose intolerance and milk allergy.
Meta Description: [ Lactose intolerance and milk allergies are very common but remain underestimated. This is a comprehensive guide about these conditions and about Irritable Bowel Syndrome. We discuss their symptoms, treatments, causes, and genetics. Guidance about hidden milk products, calcium supplements and lact... ]
Lactose.com.au - Provides general information for the lactose intolerant, with particular focus on Australia.
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Milk Allergy and Lactose Intolerance - Informational site with a particular focus on lactose intolerance in Australia.
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Milk/Casein/Lactose-Free List - An open, unmoderated discussion list for those following a milk/casein/lactose-free diet, and for people with an interest in milk-free issues. Search the archives, join the list and post a message from this site.
National Dairy Council: Lactose Maldigestion or Intolerance - Dairy industry information sheet on lactase deficiencies, with advice about milk products that some people are able to consume without symptoms.
NIDDKD - Lactose Intolerance - An overview of lactose intolerance, with information on diagnosis, treatment, nutritional concerns, and dietary measures.
No Cow's Milk for Me Thanks! - UK website for people with lactose intolerance and cow's milk allergies. Advice about symptoms, test, and management, including finding dairy-free products.
Meta Description: [ No cow's milk for me thanks!, No cow's milk for me thanks! ]
No Milk Page - Annotated links to sites for people wishing to avoid dairy products for health or other reasons. Examples are lactose maldigestion, milk allergy, milk protein intolerance, casein intolerance, and the vegan diet.
Meta Description: [ A page of many annotated links to sites for people wishing to avoid dairy products for health or other reasons. Examples are lactose maldigestion, milk allergy, milk protein intolerance, casein intolerance, and the vegan diet. ]
NoWhey.org - Site dedicated to helping people with lactose intolerance. It contains lots of practical advice on how to shop and eat out and avoid products that contain lactose.
Questionnaire on Lactose Intolerance - Research questionnaire investigating the eating habits, difficulties, symptoms and diet of lactose-intolerant people ages 18 and over. Available in several languages. Also general information and internet links on the condition.
Meta Description: [ consultations diététiques - information nutritionnelle ]
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Topics in Osteoporosis: Lactose Intolerance - Summary discussion of the relationship of lactose intolerance and lactose maldigestion to loss of bone density. From NIH-supported resource center.
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Virtual Hospital: Lactose Intolerance - Information sheet for medical providers working with adult patients provides a brief overview of the causes, symptoms, diagnosis, and management of this condition.
Meta Description: [ Virtual Hospital was a digital library of health information in pediatrics, paediatrics, and radiology for pediatric education and radiology education ]
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