Re: Delurking with Dog Question - Chris

[Guest guest]

>

>On 9/10/06, Suze Fisher <s.fisher22@...> wrote:

>> If so, I doubt Charly is

>> getting adequate vit. D from sunshine due to the latitude,

>

>Unless this study failed to account for a greater concentration of

>7-dehydrocholesterol in the fur, neither dogs nor cats are capable of

>obtaining vitamin D from the sun at any latitude:

>

>==========================

>http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed & cmd=Retriev

e & dopt=AbstractPlus & list_uids=7843559 & query_hl=6 & itool=pubmed_docsum

>

>Dietary Vitamin D Dependence of Cat and Dog Due to Inadequate

>Cutaneous Synthesis of Vitamin D

>

>K. L. How, H. A. W. Hazewinkel and J. A. Mol

>

>Abstract

>As in herbivores and omnivores, the biosynthesis of vitamin D3 in the

>skin exposed to ultraviolet (uv) light is generally expected to also

>occur in the dog and the cat. The purpose of this in vitro study was

>to measure the concentrations of vitamin D3 and its precursor 7

>dehydrocholesterol (7DHC) in dog and cat skin before and after a

>quantitatively and qualitatively standardized exposure to uv light.

>The results are compared to those obtained by the same method in the

>skin of the rat. The efficiency of extracting 7DHC and vitamin D3 from

>skin was 72 ± 8% and 67 ± 3%, respectively. In dog and cat skin the

>concentrations of nonesterified 7DHC were below the detection limit of

>the HPLC system. Therefore, skin extracts were saponified and total

>7DHC and vitamin D3 concentrations were measured by normal-phase HPLC.

>Before irradiation with uv-B light the total concentrations of 7DHC

>were 1858 ± 183, 1958 ± 204, and 17,620 ± 2345 ng/cm2 skin (mean ±

>SEM; n = 5) for the dog, the cat, and the rat, respectively. The

>corresponding concentrations of vitamin D3 were 211 ± 44, 193 ± 18,

>and 161 ± 32 ng/cm2 skin for the dog, the cat, and the rat,

>respectively. Irradiation of standard solutions of 7DHC with 0.15 J

>uv-B light/min resulted in a time-dependent decrease in 7DHC and a

>concomitant increase in previtamin D3. After exposure of skin to a

>total of 2.25 J uv-B light no significant changes in concentrations in

>vitamin D3 were found in extracts of the skin of the dog and the cat,

>whereas a 40-fold increase in the vitamin D3 concentration occurred in

>the skin of the rat. It is concluded that in the skin of the dog and

>the cat only low concentrations of esterified 7DHC are present and

>that this 7DHC is also inadequately converted to vitamin D3. As shown

>previously there is no detectable increase in vitamin D3 in the dog

>exposed to uv irradiation in vivo. Therefore, these low 7DHC

>concentrations are not caused by high turnover of 7DHC but are due to

>restricted availability of this vitamin D3 precursor in the skin of

>the dog. Thus, the dog and the cat are, unlike herbivores and

>omnivores, not able to synthesize vitamin D3 adequately in the skin

>and are mainly dependent on its dietary intake, i.e., vitamin D3 is an

>essential vitamin for the dog and cat.

>=============

>

>Chris

In another post you said you don't think dogs and cats make vit D3 in the

fur and this study suggests " that they basically don't make any significant

vitamin D at all. They'd have to study the fur directly, though, to fully

confirm it. "

If other mammals make it in the fur, why not dogs and cats? This study only

tested what's made in the *skin*. Are you extrapolating from rats because

they produce a lot of vit. D3 in the skin and their fur essentially limits

their vitamin D3 production?

If most other animals make it in their fur (per Cannell) and ingest it from

self-grooming, why would it be more reasonable to extrapolate from rats than

extrapolate from what's assumedly a much larger group of mammals that

produce vit. D3 in their fur?

Suze

[Guest guest]

On 9/21/06, Suze Fisher <s.fisher22@...> wrote:

> If other mammals make it in the fur, why not dogs and cats? This study only

> tested what's made in the *skin*. Are you extrapolating from rats because

> they produce a lot of vit. D3 in the skin and their fur essentially limits

> their vitamin D3 production?

I wasn't able to view the full text of the study, so I don't know if

they attempted to rule out a fur effect or not, nor if they reviewed

the literature on fur/skin synthesis in mammals, which would be

helpful.

In any case, rats make their vitamin D in their fur under normal

conditions. The fur covers the skin, so they don't make it in their

skin. You can induce vitamin D toxicity by shaving rats and exposing

them to UV light, if I remember right. Since the fur follicles are

embedded in the skin, the only way to oil the fur with the

7-dehydrocholesterol is to supply it directly from the skin.

Therefore, it is difficult to imagine how dogs and cats could get an

adequate supply of 7-dehydrocholesterol in their fur while having

neglible concentrations in their skin.

Although I'd like to see a study on fur synthesis, I would interpret

the uncertainty in favor of a higher probability that dogs and cats

cannot synthesize significant quantities of vitamin D than the

probability that they can.

Chris

--

The Truth About Cholesterol

Find Out What Your Doctor Isn't Telling You:

http://www.cholesterol-and-health.com