From: sbharris@ix.netcom.com(Steven B. Harris)
Subject: Re: Beta carotene non-toxic.  Why?
Date: 29 Apr 1997
Newsgroups: sci.med

In <5k32dm$k5q$2@gail.ripco.com> phyllis@ripco.com (Phyllis Eisenstein)
writes:

>Can anyone tell me why beta carotene is not toxic (although vitamin A is)?
>Phyllis Eisenstein (phyllis@ripco.com)



It probably comes down to the fact that vitamin A is an analogue of
some of the body's more important development and growth regulation
hormones.  Too much and you get signals crossed.  Beta carotene is just
a fat soluable non-toxic dye.

                                      Steve Harris

From: sbharris@ix.netcom.com(Steven B. Harris)
Newsgroups: sci.med.nutrition
Subject: Re: Vitamin A Megadose hazard?
Date: 31 Jan 1999 06:03:55 GMT

In <36B3C729.6011@netcom.ca> Tom Matthews <tmatth@netcom.ca> writes:

>Stewart Rowe wrote:
>>
>> My wife is upset over a news story that high doses of Vitamin A caused
>> damage to bones. I think the case was from Norway. I've searched the
>> usual health news sites and can't find a thing. Has anyone any data
>> on this story?
>
>The following abstract is likely the study on which the news story was
>based.
>
>Ann Intern Med 1998 Nov 15;129(10):770-8
>Excessive dietary intake of vitamin A is associated with reduced bone
>mineral density and increased risk for hip fracture.
>Melhus H, Michaelsson K, Kindmark A, Bergstrom R, Holmberg L, Mallmin H,
>Wolk A, Ljunghall S
>University Hospital, Uppsala, Sweden. Hakan.Melhus@medicin.uu.se
>
>BACKGROUND: The highest incidence of osteoporotic fractures is found in
>northern Europe, where dietary intake of vitamin A (retinol) is unusually
>high. In animals, the most common adverse effect of toxic doses of
>retinol is spontaneous fracture. OBJECTIVE: To investigate whether
>excessive dietary intake of vitamin A is associated with decreased bone
>mineral density and increased risk for hip fracture. DESIGN: A
>cross-sectional study and a nested case-control study. SETTING: Two
>counties in central Sweden. PARTICIPANTS: For the cross-sectional study,
>175 women 28 to 74 years of age were randomly selected. For the nested
>case-control study, 247 women who had a first hip fracture within 2 to 64
>months after enrollment and 873 age-matched controls were selected from a
>mammography study cohort of 66,651 women 40 to 76 years of age.
>MEASUREMENTS: Retinol intake was estimated from dietary records and a
>food-frequency questionnaire. Bone mineral density was measured with
>dual-energy x-ray absorptiometry. Hip fracture was identified by using
>hospital discharge records and was confirmed by record review. RESULTS:
>In multivariate analysis, retinol intake was negatively associated with
>bone mineral density. For every 1-mg increase in daily intake of retinol,
>risk for hip fracture increased by 68% (95% CI, 18% to 140%; P for trend,
>0.006). For intake greater than 1.5 mg/d compared with intake less than
>0.5 mg/d, bone mineral density was reduced by 10% at the femoral neck (P
>= 0.05), 14% at the lumbar spine (P = 0.001), and 6% for the total body
>(P = 0.009) and risk for hip fracture was doubled (odds ratio, 2.1 [CI,
>1.1 to 4.0]). CONCLUSION: High dietary intake of retinol seems to be
>associated with osteoporosis.
>
>In US common supplemental units (but now outdated in the nutrition
>field), 1.5 mg of retinol corresponds to 5000 IU of Vitamin A, the amount
>which is contained in many dietary supplements. Because their are also
>benefits to moderate Vitamin A intake, it is too bad that the study did
>not look at more of the factors involved with bone density.
>
>Still, I would agree with the basic contention that high vitamin A
>intake is generally unwarranted unless one is using it for tumor
>inhibitory purposes.
>
>--Tom
>Tom Matthews


   I can't think of any reason supplementation with pre-formed vitamin
A is warrented at all in a healthy person who is a non-smoker.  Cats
need the stuff, but we humans can make all we need from beta-carotene,
and a few other carotenoids (provided they are present in the diet, or
supplemented).

   BTW, there is evidence that polar bears suffer more bone fractures
than their brown bear cousins, dispite a lifestyle which isn't any more
physically demanding.  So apparently even THEY haven't addapted
perfectly to the huge amounts of vitamin A they get in their diets,
dispite a million years of evolution from brown bears, in which to do
it.

                                          Steve Harris, M.D.

From: "Steve Harris" <SBHarris123@ix.netcom.com>
Newsgroups: sci.med.nutrition
Subject: Re: vitamin A
Date: Mon, 4 Jun 2001 13:09:26 -0600

"Kelolo" <kelolo01@hotmail.com> wrote in message
news:FXQS6.61$TW1.46270@news.pacbell.net...
> I've been seeing a lot of containers of vegetable juice with labels
> claiming vitamin A content.  A look at the ingredients of these juices
> reveals no animal ingredients or added vitamin A.  So how can there be
> vitamin A?  My understanding is that plants never contain vitamin A,
> only provitamins, such as beta carotene, which can be converted into
> vitamin A by most people. Is that not correct?  Can actual vitamin A be
> found in plants???

"Vitamin A" is not a chemical name, okay? It's a generic term for vitamin
activity from many sources, including certain carotenoids, which are summed
into the vitamin A activity according to a formula which involves how well
the body breaks them down and what they are broken into.

"Provitamin" is in some sense a bad term. Most of the molecules we think of
as vitamins are provitamins in the sense that they aren't the ultimate
coenzyme or modified form used by the body. Nicotinic acid is a provitamin.
Pryidoxine is a provitamin, and cyanocobalamin. But thinking of them as
provitamins doesn't help your understanding any, when it comes to how much
of them are in foods and what you should call them on a label.

From: "Steve Harris" <SBHarris123@ix.netcom.com>
Newsgroups: sci.med.nutrition
Subject: Re: vitamin A
Date: Mon, 4 Jun 2001 21:27:00 -0600

"Kelolo" <kelolo01@hotmail.com> wrote in message
news:xQRS6.108$TW1.60675@news.pacbell.net...
> The NIH disagrees with you.  According to them, "vitamin A" is a group of
> specific fat-soluble substances that have well defined biological roles.
> Their literature draws a clear distinction between what is vitamin A and
> what merely has vitamin A activity.

If it did, that would clearly be nonsense, now wouldn't it?  Think about it.
You can't win at this.

Since "vitamin A" is not a chemical, you're left with only one good way to
define it as a group of substances, and that is by its vitamin activity.
And that is what you're seeing on the food labels: vitamin A activity for
the average human from this food.

Yes, historically there are vitamin A1 and vitamin A2 and these different
chemicals, but it's not ancient history you're reading on the labels, or
else you'd be seeing vitamin H there too.

SBH