Vitamin D is a vital nutrient that is unique, both in terms of its physiology and because humans rely on both endogenous skin production and exogenous sources to meet biological requirements. Vitamin D is commercially available as vitamin D2, (ergocalciferol) made from plant products, and vitamin D3, (cholecalciferol) made from animal products.
Cholecalciferol is also made naturally in the skin by the action of a specific wavelength of ultraviolet light (UVB) interacting with precholesterol. Cholecalciferol is then transported to the liver and turned into calcidiol [(25(OH)D]. In turn, the calcidiol is transported to the kidney and transformed into the steroid calcitriol, which is excreted into the blood to help regulate calcium in the body. This is the main endocrine function of vitamin D.
Meanwhile, many tissues other than the kidney turn calcidiol into calcitriol to help regulate gene expression locally; this is the newly discovered autocrine (inside the cell) and paracrine (surrounding the cell) functions of vitamin D. This autocrine and paracrine function is impaired in vitamin D deficient subjects. All studies show many Americans are vitamin D deficient, especially Blacks, where the problem is pandemic.
This use of calcitriol by other tissues as an autocrine and paracrine hormone is a relatively new discovery that explains its role in human development as well as the many health benefits of vitamin D in other illnesses such as diabetes, hypertension, heart disease, autoimmune illness, at least 13 different cancers and, perhaps, some mental illness.
The Extraordinary Rate of Natural Vitamin D Production
The single most important scientific fact about vitamin D is that young adult Whites make about 20,000 units of vitamin D in their skin within minutes of whole-body, summer-sun exposure. This is 100 times the Adequate Intake (AI) and five times the toxicity maximums (Lowest Observed Adverse Effects Level or LOAEL) recommended by the Institute of Medicine (IOM) for young adults. Therefore, many Americans greatly exceed the IOM’s safety recommendations by simply spending a few minutes outside in their swimming suits!
This extraordinary rate of natural vitamin D production in the skin (20,000 IU) leading to the production of a potent endocrine, paracrine and autocrine steroid hormone leads one (as T.S. Eliot once said), "to an overwhelming question." Why did Nature design such a complex system reliant on rapid and bountiful production of cholecalciferol? Answer, "Probably for a very good reason."
Because low calcidiol [25(OH)D] levels (less than 35 ng/ml) are associated with so many chronic illnesses, calcidiol levels are an important part of any laboratory health evaluation and should be routinely checked by physicians. Unfortunately, few physicians are aware of this so perhaps as much as 70 percent of the U.S. population has calcidiol levels below 35 ng/ml. Even when asked to check vitamin D levels, physicians often order calcitriol levels, instead of calcidiol levels, an error that greatly misleads both the physician and the patient.
What are Optimum Blood Levels of Vitamin D?
For numerous reasons (optimal calcium absorption, maximal suppression of PTH, reduction in blood pressure, decreased incidence of various cancers, retarding the progression of osteoarthritis, reducing the incidence of autoimmune illness, reduction in CRP, etc), healthful blood levels of calcidiol [25(OH)D] are between 35 and 50 ng/ml although commercial labs usually report "normal" or Gaussian distributions of between 8-72 ng/ml depending on the latitude of the lab’s population.
Therefore, commercial reference laboratories also mislead physicians and their patients by reporting "normal" (Gaussian distributions of a deficient population) instead of healthful calcidiol levels. Patients need to know these facts before asking their physician for the calcidiol [25(OH)D] blood test.
Until the medical profession becomes knowledgeable on this matter, patients need to become educated, educate their physicians, get the proper blood test and then take steps to raise their calcidiol level if it is less than 35 ng/ml. We know of no reason to exceed 50 ng/ml.
Populations around the equator (where man evolved) and groups spending time outdoors without many clothes (lifeguards), have levels of around 50 ng/ml. Such observations have important implications for the vitamin D conditions under which humans evolved.
In other words, it suggests humans have had 25(OH)D levels of around 50 ng/ml for 99.99 percent of the time they have been on earth. Only in the last several hundred years has urbanization, industrialization, glass (UVB does not penetrate glass), excessive clothes (UVB does not penetrate clothes) and sunblock lowered 25(OH)D levels to their current deficient levels.
Options if Your Vitamin D Levels are Low
Persons with low levels have three choices: the sun, a sun lamp or vitamin D supplements. At most latitudes in the United States, little or no vitamin D is made in the skin in the late fall and early winter. In our most northern states the vitamin D blackout lasts for about six months. In the spring and summer, Whites can make large amounts (20,000 IU) by sunbathing on both sides, without sunblock, for a few minutes (about one-third the time it takes for the skin to begin to slightly redden). Darker skinned persons need five to 10 times longer depending on the amount of melanin pigment in the skin.
Vitamin D production occurs within minutes and is maximized long before the skin turns red or begins to tan. One does not have to get repeated blood tests when using sun exposure to obtain vitamin D. Toxicity can not occur even with heavy and continuous sunbathing because ultraviolet light begins to degrade vitamin D after making about 20,000 IU, thus reaching a steady state. Overexposure, especially sunburns, is damaging to the skin, dangerous, and should be entirely avoided.
Some artificial sun lamps contain significant amounts of UVB and have been shown to raise calcidiol levels into the healthful range. Just like the sum, one does not have to worry about toxicity or obtain repeated blood levels when using them. However, just like the sum, care must be taken not to overexpose the skin. Suntans are not needed to obtain adequate vitamin D. Sunburns must be avoided. One manufacturer with some vitamin D data is Sperti. (http://www.sperti.com/products.htm)
Many people are beginning to rely on supplements to raise their calcidiol levels as they have been told (usually erroneously) to entirely avoid the sun. However, in the absence of UVB, one must consume 3,000 to 5,000 IU of cholecalciferol a day to maintain healthful calcidiol levels. Similar studies have not been done with ergocalciferol but current data indicates that almost twice as much ergocalciferol would be needed.
Vitamin D repletion is safest when done under a physician’s care so calcidiol levels (and perhaps calcium levels) can be monitored. Persons diagnosed with sarcoidosis, other granulomatous disease, cancer (especially lymphoma) or hyperparathyroidism should not take vitamin D unless they are under the care of a knowledgeable physician (and would be well advised to find one). Patients with these conditions may develop a vitamin D hypersensitivity syndrome, which is different than vitamin D toxicity.
Vitamin D Toxicity
Persons who do not want to have blood tests would be best advised to rely on prudent sun exposure. If such persons choose to avoid the sun, they should never exceed 2,000 IU of cholecalciferol a day [which is the Institute of Medicine’s NOAEL (No Observed Adverse Effects Level)].
Cholecalciferol can be obtained at health food stores and on the Internet. Cod liver oil contains about 1,200 IU of vitamin D per tablespoon but also contains about 14,000 IU of vitamin A. Therefore, persons with no sun exposure may exceed safe intakes of vitamin A in order to replete the vitamin D system. (We know omega-3 nutrition is very important but believe fish oil to be a safer alternative than cod liver oil).
Vitamin D can be toxic in overdose (probably more than 20,000 IU a day over a prolonged period of time). We are not aware of any reports in the literature of deaths from acute overdose, such as suicide attempts, leading to death. In fact, a 150-pound human would have to take more than 100,000 capsules of the 1,000 IU cholecalciferol capsules to approach the LD50 for the most sensitive mammal (the male rat at 40 mg/kg).
Such patients would be more likely to die from gastric bloating leading to asphyxiation than from vitamin D toxicity. In mammals, signs of toxicity short of death can first be seen at .5mg/kg (20,000 IU/kg or 1,400 capsules at one time for a 150 pound adult human).
We are unaware of any reports of vitamin D toxicity from supplements except when manufacturing errors occurred. Most of the reported toxicity is industrial (dairies putting in the wrong amount into milk or the concentrated oil being used for cooking). However death from chronic poisoning has been described and is possible. If you believe "a little is good then a whole lot is better," then you may prove the association between judgment and natural selection.
Winter is the time of year when you need to be most concerned about the amount of vitamin D you are receiving, so this article from The Vitamin D Council could not have come at a better time.
Although the majority of Americans are deficient in vitamin D during the winter, it is essential to understand that in order to know how much vitamin D you should be taking, you should get your blood level checked. Unfortunately, very few doctors do the blood test for vitamin D. Even as the word leaks out about vitamin D to the traditional medical community, testing for vitamin D will not skyrocket like cholesterol or other testing because there is no expensive drug to push, thus making the public more aware.
You can't rely on the media to expose the issue. If and when they do, it will be too late for most of you and you will have suffered decreased bone density and an increased risk of many cancers. But you don't have to wait for the media. You can read my article on vitamin D testing and get up to date on this important topic before it is too late. Unless you are getting significant sun exposure on large amounts of your skin, in fact, I would advise reading the article right now.
The Vitamin D Council, the non-profit group that contributed the excellent article above, is another great resource for vitamin D information. The Vitamin D Council is a group of citizens concerned about vitamin D deficiency and the diseases associated with that deficiency. I encourage you to check out their website and sign up for their informative newsletter. Their goal is an important one: to draw attention to the problem of vitamin D deficiency through the education of professionals, the media, government officials and average citizens.
If you follow my newsletter then you'll know that I recommend cod liver oil as the best source of vitamin D (other than the sun, of course). You may have noticed in the above article that the author doesn't recommend taking cod liver oil for vitamin D due to its high level of vitamin A, which he believes could exceed the safe amount of vitamin A if taken regularly.
This is one point that we disagree on, as there are several reasons why the vitamin A in cod liver oil is completely safe. First of all, the main toxicity that can result from vitamin A is due to SYNTHETIC vitamin A, NOT the natural form found in cod liver oil. Secondly, cod liver oil has vitamin D in it, and it is virtually IMPOSSIBLE to become toxic on vitamin A if you take it along with vitamin D. If you'd like to look into this further, I suggest you take a look at the American Journal of Clinical Nutrition, which published a study that found Vitamin D is associated with reduced vitamin A toxicity, and the researchers observed that vitamin D appears to protect against retinal toxicity.
This study also found that the safe upper single dose of retinol IN OIL seems to be 12,000 to 18,000 units of vitamin A per kilogram of body weight. The cod liver oil that I recommend has 1,000 to 1,250 units in a one-teaspoon serving, which means that you will be way under this limit if you follow my recommended dose (one teaspoon for every 50 pounds of body weight per day).
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