Thanks, Gary, that makes sense. However, I do not...

2008-06-05T08:54:00.000+12:00

Thanks, Gary, that makes sense. However, I do note that some supplements available in NZ seem to contain excessive amounts of vitamin A. Guess it pays to read the fine print! - Alex

Alex,First of all, I am totally in agreement with ...

2008-06-04T13:31:00.000+12:00

Alex,
First of all, I am totally in agreement with Dr John Cannell's comments. It comes down to all things in moderation - not too much and not too little and in the proportions that Mother Nature intended. I would add that the sources should be natural rather than synthetic.

Natural vitamin A and the other fat soluble vitamins is sadly lacking in most of the diets that I get to analyse. Adding these vitamins back into the diet in modest amounts is different to dosing up on large quantities, especially if they are of the purified synthetic version.

For example; a cod liver oil capsule delivers 2,000iu of natural vitamin A which is at the lower end as compared to the doses Dr Cannell is talking about.

While there may be some antagonism of vitamin D, I think it is inconsequential. The bigger issue is to do with the vast majority of people not having anywhere enough vitamin D in their bodies in the first place.

Rather than cut back further on the vitamin A, it makes much better sense to increase the vitamin D.

I hope this clarifies the issue Alex.

Hi Gary: I've read a number of articles warning m...

2008-06-04T11:22:00.000+12:00

Hi Gary: I've read a number of articles warning me off vitamin A and cod liver oil. The biggest problem is that they deactivate vitamin D. Here's one blog example:

"I'm glad the improvements are continuing. I see Dr. Yasko recommends 10,000 IU of vitamin A/day as well as cod liver oil. I strongly disagree. Make sure your son is taking neither vitamin A nor cod liver oil. Rather, make sure he eats colored fruits and vegetables as well as fortified oatmeal. Vitamin A interferes with vitamin D's function, especially at the doses Dr. Yasko recommends.

"Vitamin A antagonizes the action of vitamin D. In humans, even the vitamin A in a single serving of liver impairs vitamin D’s rapid intestinal calcium response. Furthermore, the consumption of preformed retinols, even in amounts consumed by many Americans in both multivitamins and cod liver oil appears to be causing low-grade, but widespread, bone toxicity, perhaps through its antagonism of vitamin D. In a recent dietary intake study, Kyungwon et al found high retinol intake completely thwarted vitamin D’s otherwise protective effect on distal colorectal adenoma and they found a clear relationship between vitamin D and vitamin A intakes as the women in the highest quintile of vitamin D intake also ingested almost 10,000 IU of retinols/day. As early as 1933, Hess et al warned about vitamin A consumption, concluding, 'as to a requirement of thousands of units of vitamin A daily, the unquestionable answer is that this constitutes therapeutic absurdity, which, happily, will prove to be only a passing fad.'

Rohde CM, Deluca HF. All-trans retinoic acid antagonizes the action of calciferol and its active metabolite, 1,25-dihydroxycholecalciferol, in rats. J Nutr. 2005;135(7):1647-1652.

Johansson S, Melhus H. Vitamin A antagonizes calcium response to vitamin D in man. J Bone Miner Res. 2001;16(10):1899-1905.

Penniston KL, Tanumihardjo SA. The acute and chronic toxic effects of vitamin A. Am J Clin Nutr. 2006;83(2):191-201.

Oh K, Willett WC, Wu K, Fuchs CS, Giovannucci EL. Calcium and vitamin D intakes in relation to risk of distal colorectal adenoma in women. Am J Epidemiol. 2007;165(10):1178-1186.

Hess AF, Lewis JM, Barenberg LH. Does our dietary require vitamin A supplement? JAMA. 1933;101:657-663.

Unfortunately, Hess’s prophecy of a passing fad proved premature and many Americans continue to consume 'absurd' and dangerous quantities of vitamin A. For example, multivitamins, until recently, had small amounts of vitamin D (200 to 400 IU) but high amounts of preformed retinols (5,000 to 10,000 IU). This pales in comparison to a tablespoon of modern cod liver oil, which contains sub-physiological amounts of vitamin D (400 to 1200 IU) but supra-physiological amounts of completely preformed retinols (5,000 to 15,000 IU or in some cases 30,000 IU).

John Cannell

So what's the story?

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