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From: Juhana Harju on 6 Jul 2008 05:21
trigonometry1972(a)gmail.com wrote:
> On Jul 5, 9:59 pm, "Juhana Harju" <n...(a)mail.fi> wrote:
>> trigonometry1...(a)gmail.com wrote:
>>> The risks of vitamin A poisoning are somewhat
>>> overplayed.
>>
>> Acute vitamin A poisoning is rarely a problem. However, high intake
>> of vitamin A increases the resorption of bone even when vitamin D
>> intake is sufficient. In a recent study childhood cod liver oil
>> consumption was related to worse bone mineral density in adult life.
>> High serum retinol (vitamin A) level has also been related to higher
>> fracture risk.
>>
>> http://content.nejm.org/cgi/content/abstract/348/4/287
>>
> Good points. I am not a fan of cod liver oil as it currently
> formulated.
> It is my understanding cod liver is basically taken apart and put back
> together again such that the doses are as we see them on the bottle.
> Thus it has far too much vitamin A in ratio to vitamin D.
>
> Pretty clearly the vitamin A has an antagonism for vitamin D and an
> excess would surely worsen the results for some of being
> low on vitamin D.
>
> I wonder to what extent this is a two way street between these
> two vitamins?

There is a rat study showing that vitamin A increases bone resorption even
when there is enough vitamin D present.

"Regardless of the presence or absence of vitamin D(3), ATRA [all-trans
retinoic acid] was able to cause bone resorption."

J Nutr. 2003 Mar;133(3):777-83.
Bone resorption activity of all-trans retinoic acid is independent of
vitamin D in rats. Rohde CM, DeLuca H.
Department of Biochemistry, University of Wisconsin-Madison, College of
Agricultural of Life Sciences, Madison 53706, USA.

The mechanism by which all-trans retinoic acid (ATRA) induces bone
resorption is unknown. However, an interaction between vitamin A and vitamin
D has been established. In fact, although the mechanism is still unclear,
vitamin A has been shown to be a weak antagonist of the actions of vitamin
D. Taking into account this interaction and the influence of vitamin D on
other calcitropic hormones, such as parathyroid hormone, the effect of
vitamin D on ATRA-induced bone resorption was investigated. Vitamin
D-deficient rats were fed diets containing 0 or 150 micro g of ATRA/g of
diet. The rats then were orally administered 0 or 625 ng of cholecalciferol
(vitamin D(3)) daily. Various bone parameters were measured after 3-8 wk.
Regardless of the presence or absence of vitamin D(3), ATRA was able to
cause bone resorption. In addition to examining the effect of vitamin D on
ATRA-induced bone resorption under normal conditions, this effect also was
studied under conditions that inhibit bone mineralization or growth by
altering dietary calcium (Ca) and phosphorus (P) levels. Changes in dietary
levels of Ca and P did not affect the ability of ATRA to cause bone
resorption. Interestingly, despite its ability to stimulate bone resorption,
ATRA did not affect serum calcium or phosphorus levels. Overall, the ability
of ATRA to cause bone resorption is not dependent on vitamin D(3), dietary
Ca or dietary P. PMID: 12612152

http://www.ncbi.nlm.nih.gov/pubmed/12612152

Also, consider the fact that in a recent meta-analysis vitamin A
supplementation was shown to increase mortality. Although the study has been
severely criticized, the results are pretty clear when it comes to vitamin
A.

http://jama.ama-assn.org/cgi/content/abstract/297/8/842

The optimal intake of vitamin A is easily exceeded even without consuming
cod liver oil or taking vitamin A supplements, IMHO.

sci.med.diseases.osteoporosis added.

--
Juhana

Ravintoblogini:
http://ruohikolla.blogspot.com/

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