Talk:Intrinsic factor

Sequence/Discriminator

The mention of haptocorrin (HC) in this description of IF seems to be a confusion: HC is a low yield salivary component, IF is a higher yield gastric parietal cell secretion, both transport B12 out of the stomach for ileal absorption.
Wikidity (talk) 00:43, 30 November 2009 (UTC)

Regulation

How is the production of intrinsic factor regulated? An answer may be in the following article for those who have full text access: R P Ferraris, J M Diamond (1989). "Specific Regulation of Intestinal Nutrient Transporters by their Dietary Substrates". Annual Reviews in Physiology. 51: 125–141. doi:10.1146/annurev.ph.51.030189.001013. PMID 2653177.
Icek (talk) 14:11, 10 October 2008 (UTC)

factor identity

How can "enzyme-like unidentified substance" be a characterized gene, predicted protein, and have a RefSeq ID? —Preceding unsigned comment added by Twbeals31 (talk • contribs) 11:54, 8 May 2010 (UTC)

My exact question! —Preceding unsigned comment added by 184.77.100.113 (talk) 01:35, 31 October 2010 (UTC)

B12 relation to Intrinsic factor

Suggested article improvements:

• The limited amount of normal gastric intrinsic factor (GIF) limits normal efficient absorption of B12 to about 2 mcg per meal; this is a nominally adequate intake of B12.

Watanabe F. Vitamin B12 sources and bioavailability. Exp Biol Med (Maywood) 2007;232:1266–74. Abstract/FREE Full Text ajcn.nutrition.org/cgi/ijlink?linkType=ABST&journalCode=spebm&resid=232/10/1266

"the intrinsic factor-mediated intestinal absorption system is estimated to be saturated at about 1.5–2.0 μg per meal under physiologic conditions"

• older people tend to have reduced B12 absorption for various reasons

"Nearly one-third of people over age 50 suffer from atrophic gastritis, a thinning of the stomach lining that interferes with vitamin B12 absorption."

"Low levels of stomach acid can also lead to overgrowth of bacteria in the small intestine. These bacteria, in turn, leach vitamin B12 from the body. "

www.cdc.gov/ncbddd/b12/documents/b12-030910.pdf

"Among the elderly, atrophic gastritis and pernicious anemia are the main causes of malabsorption."

Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline ( 1998 )

"Because 10 to 30 percent of older people may be unable to absorb naturally occurring vitamin B12, it is advisable for those older than 50 years to meet their RDA mainly by consuming foods fortified with vitamin B12 or a vitamin B12-containing supplement."

www.merckmanuals.com/home/disorders_of_nutrition/vitamins/vitamin_b12.html

"Among older people, absorption may be inadequate because stomach acidity is decreased. Decreased stomach acidity reduces the body's ability to remove vitamin B12 from the protein in meat. However, the vitamin B12 found in vitamin supplements can continue to be well absorbed even in people with decreased stomach acid."

• The liver normally stores 3-5 years of B12. The natural depletion rate of these liver stores is about 0.1% per day.

www.merckmanuals.com/home/disorders_of_nutrition/vitamins/vitamin_b12.html

"Unlike most other vitamins, B12 is stored in substantial amounts, mainly in the liver, until it is needed by the body. If a person stops consuming the vitamin, the body's stores of this vitamin usually take about 3 to 5 years to exhaust."

www.veganhealth.org/b12/dig

"Various studies have indicated that .1-.2% of the body's B12 pool is lost per day; the .2% loss occurs in those with pernicious anemia (5)

The average nonvegetarian stores 2,000-3,000 µg B12 (5), while losing only about 3 µg/day (6). About 60% of the total amount of B12 in the body is stored in the liver and 30% is stored in the muscles (4).

The body has a special circuit between the digestive tract and the liver. Bile, which is made in the liver and needed to digest fat, is secreted into the beginning of the small intestine. It is then reabsorbed at the end of the small intestine (the ileum) and taken back to the liver where it is used again. This circuit is called enterohepatic circulation.

People normally secrete 1.4 µg/day of B12 into their small intestines via their bile (5). Consequently, healthy people can reabsorb about .7µg B12/day from their bile (5)."

4. Messina M, Messina V. The Dietitian's Guide to Vegetarian Diets. Gaithersburg, MD: Aspen Publishers, Inc., 1996.

5. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press; 2000. www.nap.edu/catalog/6015.html

6. von Schenck U, Bender-Gotze C, Koletzko B. Persistence of neurological damage induced by dietary vitamin B-12 deficiency in infancy. Arch Dis Child. 1997 Aug;77(2):137-9.

• IF is necessary for efficient absorption of B12. Without IF, the intestines can directly absorb about 1% of ingested B12. Oral supplement of 500-1000 mcg (readily available OTC) per day generates adequate direct absorption without functioning IF.

www.veganhealth.org/b12/dig

"In addition to the IF mechanism, passive diffusion normally accounts for 1-3% of B12 absorbed when obtained through normal food sources (3)."

3. Groff J, Gropper S. Advanced Nutrition and Human Metabolism, 3rd ed. Wadsworth: 2000.

www.aafp.org/afp/2003/0301/p979.html

"Even when intrinsic factor is not present to aid in the absorption of vitamin B12 (pernicious anemia) or in other diseases that affect the usual absorption sites in the terminal ileum, oral therapy remains effective."

"Although the daily requirement of vitamin B12 is approximately 2 mcg, the initial oral replacement dosage consists of a single daily dose of 1,000 to 2,000 mcg (Table 4). This high dose is required because of the variable absorption of oral vitamin B12 in doses of 500 mcg or less.19 This regimen has been shown to be safe, cost-effective, and well tolerated by patients.19"

www.veganhealth.org/b12/formula#older

"A 2005 clinical trial from the Netherlands found that among people aged 70-94, who had vitamin B12 deficiency but were otherwise healthy, 16 weeks of 500 µg/day of cyanocobalamin was required to get MMA levels in the healthy range. Other doses tested were 2.5, 100, 250, and 1,000 µg (16)."

16. Eussen SJ, de Groot LC, Clarke R, Schneede J, Ueland PM, Hoefnagels WH, van Staveren WA. Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch Intern Med. 2005 May 23;165(10):1167-72. | link www.ncbi.nlm.nih.gov/pubmed/15911731

-71.174.175.150 (talk) 19:51, 3 January 2015 (UTC)

Name

Why is it called intrinsic factor? Nanonic (talk) 03:17, 29 August 2023 (UTC)