Hello aussie2,
It turns out that both your questions relate to the bacteria that
colonize the colon.
The bacteria of the colon produce vitamin K, which is important in the
mechanisms which enable blood to clot:
“Vitamin K is a necessary participant in synthesis of several proteins
that mediate both coagulation and anticoagulation. Vitamin K
deficiency is manifest as a tendency to bleed excessively… the chief
source of vitamin K is synthesis by bacteria in the large intestine,
and in most cases, absence of dietary vitamin K is not at all
deleterious. Vitamin K is a fat-soluble vitamin and both dietary and
microbial vitamin K are absorbed into intestinal lymph along with
other lipids.”
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/misc_topics/vitamink.html
Bacteria in the colon also produce B complex vitamins, including
vitamin B12. B12 is only produced by bacteria and, despite claims
made for spirulina and some other vegetable products, it is generally
accepted that the only human dietary source is from animal products.
Vegans need to take B12 supplements in order to maintain health. Some
years back, it was suggested that vegans could make use of B12
produced by their colonic bacteria and therefore avoid deficiency even
without supplementation. However, it was then established that B
vitamins are not readily absorbed from the colon, and therefore to
make use of those produced by colonic bacteria would require a
behaviour modification that would NOT suit most people: “…formation of
B vitamins by the microbial flora in the large intestine is useful to
many animals. They are not absorbed in the large intestine, but are
present in feces. The behavior of coprophagy or eating feces seen
particularly in rodents, rabbits and other animals is thought to be a
behavioral adaption to recovery of these valuable resources.”
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/largegut/ferment.html
Both the above links are to extracts from “Pathophysiology of the
Digestive System” at Colorado State University.
However, science does not stand still. A paper published in 1998 in
the American Journal of Physiology (Volume 275(5 Pt 1), pages
C1365-71) “Biotin uptake by human colonic epithelial NCM460 cells: a
carrier-mediated process shared with pantothenic acid.” by Said HM,
Ortiz A, McCloud E, Dyer D, Moyer MP, Rubin S. of Veterans Affairs
Medical Center, Long Beach 90822, California, reported evidence that
the cultured cells derived from those which line the colon are able to
take up biotin and pantothenic acid (members of the B-complex
vitamins):
“Previous studies showed that the normal microflora of the large
intestine synthesizes biotin and that the colon is capable of
absorbing intraluminally introduced free biotin. Nothing, however, is
known about the mechanism of biotin absorption in the large intestine
and its regulation. To address these issues, we used the
human-derived, nontransformed colonic epithelial cell line NCM460….
These results demonstrate, for the first time, the functional
existence of a Na+ [sodium]-dependent, specialized carrier-mediated
system for biotin uptake in colonic epithelial cells. This system is
shared with pantothenic acid and appears to be under the regulation of
an intracellular PKC [protein kinase C]-mediated pathway.”
The full text is available on the journal’s web site at
http://ajpcell.physiology.org/cgi/content/full/275/5/C1365
More recent papers from the same research group report similar results
for the uptake of thiamine and riboflavin:
Said HM, Ortiz A, Subramanian VS, Neufeld EJ, Moyer MP, Dudeja PK.
“Mechanism of thiamine uptake by human colonocytes: studies with
cultured colonic epithelial cell line NCM460.
American Journal of Physiology, Gastrointestinal and Liver Physiology,
2001 July, Volume 281(1), pages G144-50.
Full text at
http://ajpgi.physiology.org/cgi/content/full/281/1/G144
Said HM, Ortiz A, Moyer MP, Yanagawa N.
Riboflavin uptake by human-derived colonic epithelial NCM460 cells.
American Journal of Physiology, Cell Physiology, 2000 Feb, Volume
278(2), pages C270-6.
Full text at
http://ajpcell.physiology.org/cgi/content/full/278/2/C270
If these studies are confirmed by other scientists, and if they are
found to apply to colon cells in the body as well as to cultured
cells, we may come back to the view that colonic bacteria can be a
significant source for humans of at least some B vitamins.
With respect to cholesterol, again the information I found relates to
the gut bacteria.
The speed with which cholesterol is broken down by bacteria in the
colon can influence the risk a person has of getting colon cancer, and
this risk can be lessened by dietary modifications, such as increasing
intake of fiber and probiotics such as Lactobacillus (yogurt bacteria)
American Journal of Clinical Nutrition 1976 Dec, Volume 29(12), pages
1455-60
Metabolic epidemiology of colon cancer: enzymic activity of fecal
flora.
Mastromarino A, Reddy BS, Wynder EL.
“Because of the potential significance of secondary bile acids and
cholesterol metabolites formed by the intestinal microflora in the
pathogenesis of colon cancer, fecal microbial 7alpha-dehydroxylase and
cholesterol dehydrogenase activities were assayed in colorectal cancer
patients, patients with adenomatous polyps, asymptomatic controls, and
normal controls…. The mean cholesterol dehydrogenase activity for
colorectal cancer patients was significantly greater than controls.
Patients with polyps also had greater activity than controls…. These
data support the concept that patients with colorectal cancer are more
able to convert primary bile acids and cholesterol to microbial
products in colon contents than are controls.”
Summary at
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=793371&dopt=Abstract
“Research has shown that diets high in fiber, particularly insoluble
fiber, protect against colon cancer. By binding with bile acids, which
in high concentrations are thought to contribute to the development of
malignancies, fiber appears to protect the inner lining of the colon.
Furthermore, fiber hastens the amount of time it takes for feces to be
eliminated, thereby minimizing the colon's exposure to naturally
occurring carcinogens—including byproducts of intestinal bacteria,
substances derived from the breakdown of cholesterol, and compounds
produced by meat cooked at high temperatures.”
http://www.emory.edu/EMORY_REPORT/erarchive/1996/May/ERmay.6/5_6_96wellness.html
Emory Report, May 6, 1996, Volume 48, No. 32
Scandinavian Journal of Infectious Diseases (Supplement) 1986, Volume
49, pages17-30
Bengt E. Gustafsson memorial lecture. Function of the normal human
microflora.
Gorbach SL.
“The normal human microflora maintains a delicate balance between its
constituent parts, numbering 10(11) bacteria per gram with over 400
different species…. play a role in metabolizing nutrients, vitamins,
drugs, endogenous hormones and carcinogens. Our laboratory has studied
estrogen and cholesterol metabolism and activation of colon
carcinogens…. Switching the diet from an omnivore diet to a
vegetarian diet decreases bacterial deconjugating enzymes in the
intestine. Administering antibiotics also suppresses the metabolic
activity of the microflora. Similar suppressive effects can be
achieved by feeding a human strain of Lactobacillus that implants in
the gastrointestinal tract.”
Abstract at
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3103209&dopt=Abstract
Nutrition Review, 1991, July, Volume 49(7), pages 195-203
Soluble fiber polysaccharides: effects on plasma cholesterol and
colonic fermentation.
Topping DL.
CSIRO Division of Human Nutrition, Glenthorne Laboratory, Australia.
“Many soluble-fiber polysaccharides, used as stabilizers and
thickeners by the food industry, lower plasma cholesterol and slow
small intestinal transit and nutrient absorption. Although
nondigestible by human enzymes, these polysaccharides are fermented by
the large-bowel microflora, yielding short-chain fatty acids…
Short-chain fatty acids do not seem to mediate effects of fiber on
plasma cholesterol, but in the large bowel they exert the trophic and
antineoplastic [anti-cancer] effects of dietary fiber. The mechanism
for cholesterol reduction by soluble fibers relates to enhanced
steroid excretion and altered fat absorption and may be a function of
the viscosity of these fibers in solution.”
Abstract at
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1658695&dopt=Abstract
And there seems to be a link between cholesterol metabolism by colon
bacteria and the risk of developing gall stones:
British Medical Journal (Clinical Research and Education), 1981 Mar
28, Volume 282(6269), pages 1018-20
Do colonic bacteria contribute to cholesterol gall-stone formation?
Effects of lactulose on bile.
Thornton JR, Heaton KW.
“Lactulose… was taken as a proprietary syrup for six weeks… All
subjects showed a fall in the percentage of the 7-alpha-dehydroxylated
bile acid deoxycholic acid… and a rise in the percentage of the
primary bile acid chenodeoxycholic acid… Bile was initially
super-saturated with cholesterol in most subjects and became less
saturated with cholesterol in all but one… These data support the
theory colonic bacteria contribute to cholesterol gall-stone
formation.”
Abstract at
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6783227&dopt=Abstract
1. colon cholesterol metabolism site:.edu 2. colon vitamins site:.edu
(NB I restricted the search to .edu sites in order to eliminate the
thousands of commercial sites selling food supplements and to find
only academically verified material)
Medline searches at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi on:
colon cholesterol bacteria
I hope this answers your question sufficiently. If not, please request
clarification before rating. |
,
0 Comments
)