http://jn.nutrition.org/cgi/content/abstract/129/4/903Cats may need the vitamin d precursor 7-dehydrocholesterol in the diet in order to produce enough vitamin d. The kittens in the study certainly do.
http://www.bioone.org/doi/abs/10.1290/1071-2690%282000%29036%3C0201%3AAHSEMT%3E2.0.CO%3B2the second study mentions concentrations of 7-dehydrocholesterol in human skin.
http://www.springerlink.com/content/x10l60x7t43g8446/This third covers a cholesterol lowering drug that increases synthesis of vitamin d by reducing the conversion of 7-dehydrocholesterol into cholesterol.
A few questions come to mind.
1) Are there cholesterol lowering drugs that lower synthesis of vitamin d, because their action comes earlier in the chain of events that leads to 7-dehydrocholesterol and then cholesterol?
2) According to the first study, rodents such as mice and rats have much larger concentrations of 7-dehydrocholesterol than animals like pigs and sheep, the theory being that it's a prerequisite of the feline diet. I wonder if smaller animals in general have larger amounts of this stuff, or just rodents? Mice and rats are kind of adolescent all of their lives; after a certain age, people stop growing longer and only grow wider, whether in muscle, bone or fat. People aren't cats, but is it possible that it's also a conditional prerequisite of our diet? Further to this question, it's well known that diet can have a wide range of effects on cholesterol synthesis in humans. Can this have an affect on vitamin d synthesis?
Some points; Dr Davis of Heartscan Blog relates that his patients often have a large increase of large HDL particles (the good ones) when they optimize their serum vitamin d. Also, but I haven't looked into this too deeply, I've read reports that people have lower levels of cholesterol in the summer and higher in the winter. Also something about more heart attacks in the winter than the summer.
As people age, they produce less of their own vitamin d. Dr Davis has speculated, very carefully, much more carefully than a naive hack like myself would tend to, that vitamin d might extend lifespan.
http://www.westonaprice.org/moderndiseases/benefits_cholest.htmlThat's the article "The benefits of high cholesterol" by Uffe Ravnskof.
First couple paragraphs;
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People with high cholesterol live the longest. This statement seems so incredible that it takes a long time to clear one´s brainwashed mind to fully understand its importance. Yet the fact that people with high cholesterol live the longest emerges clearly from many scientific papers. Consider the finding of Dr. Harlan Krumholz of the Department of Cardiovascular Medicine at Yale University, who reported in 1994 that old people with low cholesterol died twice as often from a heart attack as did old people with a high cholesterol.1 Supporters of the cholesterol campaign consistently ignore his observation, or consider it as a rare exception, produced by chance among a huge number of studies finding the opposite.
But it is not an exception; there are now a large number of findings that contradict the lipid hypothesis. To be more specific, most studies of old people have shown that high cholesterol is not a risk factor for coronary heart disease. This was the result of my search in the Medline database for studies addressing that question.2 Eleven studies of old people came up with that result, and a further seven studies found that high cholesterol did not predict all-cause mortality either.
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I don't think it puts me too much further out on a limb than usual to point out that high cholesterol production in the elderly might coincide with high production of 7-dehydrocholesterol and thus high ability to produce their own vitamin d? Vitamin d production in centenarians isn't particularly high, but how high is it in people who died in their seventies or eighties, twenty or thirty years ago?
Going back to the mouse/rat thing. I don't think mice or rats have ever been a major part of the human diet. But some other creatures, I'm thinking shrimp, krill, smaller shellfish, are high in cholesterol, and also share the trait of growing not only wider but also longer for pretty much their whole lifespans.
http://books.google.ca/books?id=FvH7ySek6yAC&pg=PA5&lpg=PA5&dq=7+dehydrocholesterol+shrimp&source=bl&ots=4PuKJXGhQZ&sig=eeAM0tnLAYSltQGEQh3rlQCc88w&hl=en&ei=VvzESZieE9TxnQfVnJjMDQ&sa=X&oi=book_result&resnum=2&ct=result#PPA5,M1"Vitamin D Analogs in Cancer Prevention and Therapy" By Jörg Reichrath, Michael Friedrich, Wolfgang Tilgen
Yup. lots of 7-dehydrocholesterol in brine shrimp, anyways. Smaller the better?
Lie around on the beach eating shrimp? Sounds like a worthy experiment.
That's enough blathering for now.
