Did you see the recent articles about vitamin D in Newsweek or the Boston Globe? Why all this excitement about vitamin D? We all know that vitamin D (cholecalciferol) is crucial to health. But is vitamin D really a vitamin? Is it in the foods humans normally consume? Although there is some in fatty fish, vitamin D is not in our diets unless humans first fortify a food, like vitamin D fortified milk. Nature intended you to make it in your skin, not put it in your mouth. So is vitamin D really a vitamin?
Mechanism of action
Unlike any other vitamin, vitamin D is actually a prehormone; it is your body’s only source of potent steroid hormone called calcitriol. First, you skin makes vitamin D when sunlight strikes a precholesterol molecule. Then your liver converts vitamin D into the storage form of vitamin D, called calcidiol (25-hydroxy vitamin D). The body stores calcidiol in the blood and fat for later use. Your doctor can measure calcidiol with a blood test to find out if you are vitamin D deficient. Ideal calcidiol (25-hydroxy vitamin D) levels are between 35 to 65 ng/ml (87 to 162 nm/L), year around.
If you have enough calcidiol in your blood, then the real action starts. Some calcidiol goes to the kidneys to help maintain blood calcium levels but the real story is in your tissues. Tissues all over your body convert calcidiol into calcitriol. Calcitriol, or activated vitamin D, is the most potent steroid hormone in the human body. Again, calcitriol is the most potent steroid hormone in your body; it is active in picogram quantities or 1/1,000,000,000,000 of a gram. Like all steroid hormones, calcitriol works by turning your genes on and off. That is, in hundreds of tissues throughout your body, calcitriol demasks your genome! It signals your genes to make hundreds of enzymes and proteins crucial to maintaining health and fighting disease.
All this happens if, and only if, you get enough vitamin D from sunshine or from supplements. If you totally avoid the sun, recent research indicates you need about 4,000 units of vitamin D a day! So you can’t get enough vitamin D from milk (unless you drink 40 glasses a day) or from a multivitamin (unless you take about 10 tablets a day), neither of which is recommended. If you don’t get vitamin D the way Mother Nature intended, from sunshine, you need to take vitamin D supplements. As most of us get a lot more vitamin D from sunshine than we think, most of us need about 2,000 units a day extra. More and more Internet and health food stores are selling vitamin D. Make sure the vitamin D you buy is cholecalciferol. Also, buy pure cholecalciferol, don’t buy a preparation with vitamin A added. Just plain cholecalciferol.
Many of the diseases of modern civilization, such as cancer, heart disease, diabetes, hypertension, periodontal disease, depression, and even obesity, are now clearly associated with vitamin D deficiency. But association is not the same as causation. Does vitamin D deficiency cause many cases of cancer, heart disease, diabetes or obesity, these diseases of modern civilization? We just don’t know. We need the National Institutes of Health to fund more research on vitamin D. So far, they refuse.
The facts of vitamin D
If you want to understand vitamin D, you need to understand three facts. All three facts have been generally ignored by all but a few vitamin D scientists. Aldous Huxley once said, “Facts do not cease to exist, just because they are ignored.” Two of these ignored facts are simple and one is more complex.
The first fact you already know. The active form of vitamin D is a steroid hormone, a very potent steroid hormone, the most potent steroid hormone in the body. Steroid hormones work by demasking the genome, that is, they enable the manufacturing of proteins and enzymes by your genetic material, the stuff of life. So the active form of vitamin D acts by enabling genetic expression of proteins and enzymes crucial to health in hundreds of tissues throughout the body. This fact explains why vitamin D deficiency is involved in so many different diseases.
The second fact changed my life. It made me ask why? The fact is this: most of us make about 20,000 units of vitamin D after about 20 minutes of summer sun. [For most skin types, a full body minimal erythemal (slight redness) dose of UVB light results in the production of about 20,000 units of cholecalciferol]. This is about 100 times more vitamin D than the government says you need every day.
Ask yourself why? Why would humans make so much vitamin D, so very quickly? I have thought about it, studied textbooks, researched the medical literature, asked all the experts, and dedicated the rest of my professional life to getting others to ask themselves “why.” Why would we have a steroid hormone system that makes so much substrate so very quickly?
The only answer anyone can come up with is: “Probably for a good reason.” Science does not know why. Zoologists know nature does not design systems as complex as the vitamin D steroid hormone system for no reason. Medical science simply doesn’t know why we have the capacity to make so much vitamin D so quickly. If you think about it long enough, you too will conclude it is probably for a good reason. Although we don’t know why, a few scientist have been trying to find out why — and gasping at the breathtaking implications.
This second fact (20,000 units in a few minutes) also tells you something about the normal human condition — and the current deviant one. Before we started living in buildings and cars, and wearing sun-protective clothes and lathering on the sunblock, we farmed and hunted. Before then we scavenged naked in the subequatorial African sun (for more than a million years). How much vitamin D did we get then? A lot.
We started moving inside during the industrial revolution and now the move is almost complete. Some of us go for days, weeks, or even months without letting sunshine strike our skin and make vitamin D. If we do go in the sun, our dermatologist chides us. Whether good or bad, this existence is aberrant to the species; modern sun-avoidance is deviant for homo sapiens. Since we make about 20,000 units of vitamin D with a few minutes of sunshine (perhaps 10,000 units after our skin tans) then human beings are used to getting a lot of vitamin D every day, until very recently. Now, most of us get very little. This is simply deviant.
The third fact is more complex and has to do with the unique regulation of the vitamin D steroid hormone system. Steroid hormones are molecules manufactured from cholesterol and which act by effecting a receptor on the genome. Steroid hormone systems are tightly regulated by the body. When the levels are too low, the body manufactures more hormone; when levels are too high, the body makes less. Not so with vitamin D.
First, unlike other steroid systems, the vitamin D system needs both cholesterol and sunlight to get started. The body has no way of obtaining vitamin D unless you go into the sun or take supplements. That is, unlike all other steroid hormones, the body cannot manufacture its own vitamin D from cholesterol. It needs sunshine as well. Of course, until about 300 years ago, humans always had plenty of sunshine.
Remember, the real action is in the tissues. The autocrine (in the cell) and the paracrine (around the cell) vitamin D systems appear to be turned on full bore, all the time. [In scientific terms, the Michaelis Menton constant is never approached throughout the full range of physiological substrate concentrations for both calcidiol production in the liver and for calcitriol production in the tissues]. Direct negative feedback does not appear to be operating at physiological substrate levels for both calcidiol production in the liver and calcitriol production in the tissues. This implies that tissue levels may be chronically depleted in modern humans. Furthermore, we’d have no easy way of knowing we are depleted because depletion has become the normal human state.
If the tissue production of calcitriol is turned on full, all the time, what prevents vitamin D toxicity in humans living in the sun? First of all, much of the vitamin D you make is excreted in the bile. The same may be true for much of the calcidiol your liver makes. In addition, there are numerous other metabolites of vitamin D. So only about 1/1000 of your calcidiol is turned into calcitriol. That said, the tissue production of calcitriol is still running full bore at normal calcidiol substrate concentrations. So what limits the amount of tissue calcitriol?
The skin. After you make about 20,000 units, sunshine begins to destroy vitamin D in the skin. The same sunlight that makes vitamin D in the first place begins to degrade it. Production equals destruction. As calcitriol production in the tissues and calcidiol production in the liver always function below their biochemical capacity, this means that the rate limiting step for the most potent steroid hormone in the human body appears to lie in the skin. In a way, it lies in your behavior, you choice to step into the sun. This is biologically unique for any and all steroid hormones.
This third complicated set of facts strongly implies widespread severe deficiency in modern humans. When steroid hormone systems are turned on full bore, without periodically turning off, this usually means the body is asking for more hormone. Since few of us live naked in the sun, our vitamin D systems are dry, our calcidiol tanks are running on low, our tissues are starved for more of the most potent steroid hormone in the body, and, perhaps, just perhaps, diseases of civilization are rampant. That is what all the excitement is about.