I'm on a bit of a project at the moment, but I wanted to shoot off another few tidbits about vitamin D. One physician's post on an endocrinology blog ("vitamin D' is actually a steroid hormone) put it thusly:
I have included the references to each of these observations […] and draw to your attention that these have all been published in the last six months. An important exploding area of epidemiologic research. (emphasis added)
He goes on to cite seven studies, all published in the last six months. Do you want an idea of how big this is becoming? Click on this link, scroll down, and scan the headlines. Also, you can set up a Google Alert for 'vitamin d' as I have, and I get alerted to a number of new articled every single day. You can, of course, wait until I bring the best of the best to you, but I might miss something. I probably already have.
Still, you're up against a lot of idiocy, much of it from people with MDs and PhDs after their names. For instance:
Conclusions: Calcium and vitamin D supplementation did not reduce invasive breast cancer incidence in postmenopausal women. In addition, 25-hydroxyvitamin D levels were not associated with subsequent breast cancer risk. These findings do not support a relationship between total vitamin D intake and 25-hydroxyvitamin D levels with breast cancer risk.
This flies in the face of a 4-yr randomized, controlled study wherein women supplemented with vitamin D and calcium demonstrated about a 70% reduction in risk for all cancers.
The difference? In the first study, supplementation was only 400 IU per day (The USRDA for those over 50). In the second, supplementation was 1,100 IU, about three times as much daily. The first group of dimwits conclude, obviously, that vitamin D is ineffectual. I think they just want to cover their own dumb asses, because they goofed up and studied something already known: that the USRDA for vitamin D is woefully inefficient to raise blood levels (25-hyroxy) above the roughly 60 ng/mL (nanograms per milliliter) that you'd find in healthful indigenous populations that spend a lot of time outdoors and who have been verified again and again to have very low incidence of cancer (and other diseases of modern civilization).
Plus, it all makes sense from an evolutionary perspective. Being grounded in that and understanding its logic instantly alerts you to dumb-ass tomfoolery such as demostrated, above.
So, what did Rowan T. Chlebowski, et al, demonstrate? They demonstrated that the USRDA for vitamin D is horse shit, that's what they demonstrated.
So, how much should an individual take? I have no idea. How much thyroid hormone, for example, should every individual take, provided they have lower than desirable blood levels of T3 and T4? Get it? Here, let Dr. William Davis explain, a cardiologist who uses vitamin D supplementation as part of his plan of attack to detect, prevent, and reverse heart disease every day of the year (he also gets his patients 100% off all wheat and corn starch). By pure coincidence, I find that the Carlson vitamin D supplement I use is at the top of the Track You Plaque product list. I take three of those (6,000 IU) every day but fasting days. I intend to have blood levels taken soon to see where I am.
Now, a bit about vitamin A, keeping with the idiocy (Chlebowski) theme. The subject is vitamin A toxicity (fat soluble vitamins — ADE — have the potential to reach toxic levels, as they hang around and can build up). Anyway, I'm just going to quote Stephan the biologist at some length, with links, as I think it illustrates well what you're up against with much of the "unbridled reductionism" (idiocy) and the news media puppets that report it uncritically.
This is the background against which we must consider the question of vitamin A toxicity. Claims of toxicity must be reconciled with the fact that healthy cultures often consumed large amounts of vitamin A without any ill effects. Well, you might be surprised to hear me say that I do believe some Americans and Europeans suffer from what you might call vitamin A toxicity. There is a fairly consistent association between vitamin A intake and bone mineral density, osteoporosis and fracture risk. It holds true across cultures and sources of vitamin A. Chris Masterjohn reviewed the epidemiology here. I recommend reading his very thorough article if you want more detail. The optimum intake in some studies is 2-3,000 IU, corresponding to about 50% of the RDA. People who eat more or less than this amount tend to suffer from poorer bone health. This is where Dr. Cannell and others are coming from when they say vitamin A toxicity is common.
The only problem is, this position ignores the interactions between fat-soluble vitamins. Vitamin D strongly protects agains vitamin A toxicity and vice versa. As a matter of fact, "vitamin A toxicity" is almost certainly a relative deficiency of vitamin D. Vitamin D deficiency is also tightly correlated with low bone mineral density, osteoporosis and fracture risk. A high vitamin A intake requires vitamin D to balance it. The epidemiological studies showing an association between high-normal vitamin A intake and reduced bone health all sported populations that were moderately to severely vitamin D deficient on average. At optimal vitamin D levels, 40-70 ng/mL 25(OH)D, it would take a whopping dose of vitamin A to induce toxicity. You might get there if you eat nothing but beef liver for a week or two.
The experiment hasn't been done under controlled conditions in humans, but if you believe the animal studies, the optimal intake for bone mineral density is a high intake of both vitamins A and D. And guess what? A high intake of vitamins A and D also increases the need for vitamin K2. That's because they work together. For example, vitamin D3 increases the secretion of matrix Gla protein and vitamin K2 activates it. Is it any surprise that the optimal proportions of A, D and K occur effortlessly in a lifestyle that includes outdoor activity and whole, natural animal foods? This is the blind spot of the researchers who have warned of vitamin A toxicity: uncontrolled reductionism. Vitamins do not act in a vacuum; they interact with one another. If your theory doesn't agree with empirical observations from healthy cultures, it's back to the drawing board.
High-vitamin cod liver oil is an excellent source of vitamins A and D because it contains a balanced amount of both. Unfortunately, many brands use processing methods that reduce the amount of one or more vitamins. See the Weston Price foundation's recommendations for the highest quality cod liver oils. They also happen to be the cheapest per dose. I order Green Pasture high-vitamin cod liver oil through Live Superfoods (it's cheaper than ordering directly).
So is vitamin A toxicity a concern? Not really; the concern is vitamin D deficiency.