By Dr. Mercola
Vitamin D is a profoundly important nutrient that provides a vast array of health benefits. The question is, do we really need to supplement, and if we do, what's the proper dosage?
Dr. Robert Heaney is a professor and one of the most well-respected researchers in the field. He has studied osteoporosis, vitamin D, and calcium physiology for over 50 years.
Trained as a physician and endocrinologist, he’s been working at the Creighton University’s Osteoporosis Research Center, which he founded, since the late 1960s, with a focus on bone biology.
"Inevitably, when you deal with bones, sooner or later, your path crosses with vitamin D, which is ital and important for a whole host of functions," he says. "The most obvious of which is the promotion of calcium absorption, because you need calcium for bone health."
For the last two decades, Dr. Heaney has focused almost exclusively on vitamin D, noting that:
"We need to know how much we need every day. We need to know where to get it. We need to know how much the body uses every day, via what pathway and for what purposes..."
While thousands of papers have been published on the mechanisms of vitamin D, very few studies have homed in on the issue of how much you actually need, and how best to get it.
“When I first got involved with the measurement of calcium absorption, I assumed that it had all been worked out. But I found that there was not a single paper in the medical literature... that had measured how much vitamin D you needed for calcium absorption nor how much absorption a certain amount of vitamin D might produce.”
Vitamin D Is Vital for Cellular Function Throughout Your Body
According to Dr. Heaney, vitamin D is involved in the biochemical cellular machinery of all cells and tissues in your body. When you don’t have enough, that “machinery” doesn’t work very well, and your entire body will end up struggling to operate as programmed into our genomes.
Some diseases that have a long-standing association with vitamin D deficiency include rickets in children and osteomalacia (softening of your bones), but these are really only the tip of the proverbial iceberg.
“What we didn’t know until very recently is that a part of the apparatus that all cells need to open up the genome is the active form of vitamin D,” Dr. Heaney says.
"In the absence of that active form of vitamin D in the cellular environment, the cell cannot access the information in its own [genetic] plans—its DNA library...
Under those circumstances, nothing works right. The lower your vitamin D status gets, the worse the problem... [E]very tissue in our body effectively needs to have vitamin D [to optimize access its genetic code]... That's the role that vitamin D plays and it's absolutely vital."
What's an Optimal Level of Vitamin D?
According to Dr. Heaney, "the embarrassing secret about the whole field of nutrition is that we don't have any a priori idea about what normal is; absolutely no idea at all."
For example, the Institute of Medicine, in approaching most nutrients, simply defines the requirement as the least you can get by on without developing a certain disease. But this may be a far cry from what you need for optimal health, and as a general rule, many nutritional guidelines are insufficiently low.
“If you take an approach that’s based in physiology, you end up with completely different numbers,” Dr. Heaney says.
“For example, if you want to know how much vitamin D you ought to have to minimize your body’s need to compensate for the amount you’re getting – “compensate,” that is to adapt or make up for what you’re not giving it—the way to measure that is to make certain that the parathyroid hormone levels are at a functional minimum. That means that you’re not constantly having to ramp up your bone resorption in order to get the calcium you need but which you’re not absorbing.
And you’re not absorbing enough because you don’t have enough vitamin D. When you take that approach, you end up with a vitamin D requirement that produces a serum 25-hydroxyvitamin D in the range of 40 to 60 nanograms per milliliter.
Another approach [is to] ask, for instance, “How much vitamin D does a nursing mother have to take in every day in order to ensure that her milk will contain the vitamin D her nursing infant needs?”
Very recent work coming out of the Medical University of South Carolina has shown definitively that such a woman needs 6,000 international units (IU) of vitamin D per day, every day, in order for her infant to be adequately nourished, at least as far as vitamin D is concerned.”
As it turns out, the vitamin D level that a nursing mother needs to maintain is within the same range as that which minimizes the need for the parathyroid hormone adaptation, namely 40-60 nanograms per milliliter (ng/ml).
A third approach is to determine what level of vitamin D human beings have who live on the equatorial plains of East Africa. Various tribal groups living in East Africa, who still follow ancestral lifestyles, have had their blood 25-hydroxy D measured by Dutch investigators. And again, the levels they found were in the 40-60 ng/ml range.
“It’s very useful to look at what those ancestral-living humans today actually have, exposing a lot of skin and living in equatorial East Africa, where the sun shines all the time and where you can make vitamin D every day. That’s the best indicator I know of about what is optimal for our physiology,” Dr. Heaney says.
"I find it very compelling that those three distinct approaches: 1) what's the minimum compensation required, 2) what's the ancestral value, 3) and how much do you need for a critical function such as lactation—they all converge on the same numbers, somewhere in the range of 40 to 60 nanograms per milliliter of 25-hydroxy D.
The corresponding input from all sources combined is 5,000 to 6,000 international units; not just from supplements per se. We do need supplements, but the 5,000–6,000 IU figure is the total input every day needed to sustain a blood level of 40-60 ng/ml.”
What's the Ideal Way to Optimize Your Vitamin D Level?
Vitamin D is created naturally when your skin is exposed to sunshine. Interestingly, new research shows that carnivorous animals who cannot make vitamin D in their skin actually get much of the vitamin D they need from the meat they eat. This finding has led to improved understanding of food-based vitamin D. For the longest time, meat was not considered a good source of vitamin D, primarily because it was so difficult to measure that we didn’t think it contained useful amounts.
"Most of the assays that have been published up until very recently listed no vitamin D content for beef, pork, poultry, etc. Things are changing in lots of ways, [for starters], we have a much better way of measuring vitamin D than we did back then. We're now finding vitamin D present in [food] at quantities that are biologically meaningful...
My best guess – and I'm going to qualify that by saying 'guess,' because this is a moving target and we don't have all the data we need yet – is that the average adult today living in the central part of the US is getting 1,500 to 2,000 international units from food—unrecognized sources of food. They get less than we use to think from the sun... Most of us – professionals, wage slaves, workers of one kind or another – we're indoors. Not very many of us work outdoors and not very many of us get sun exposure in mid-day, and that's when you make your vitamin D."
There are also a number of other benefits associated with sun exposure that are unrelated to vitamin D production. For example, UVA exposure produces nitric oxide (NO), which has a blood-pressure lowering effect. According to Dr. Heaney, the entire solar spectrum is important for optimal health. We’re not dependent solely on the narrowband wavelength of about 295 nanometers, which is where vitamin D is made.
The Importance of Vitamin D Testing
All of that said, Dr. Heaney stresses that you need to get approximately 5,000 to 6,000 IU's of vitamin D per day from all sources – sun, supplements, and food – in order to reach and maintain a healthy blood level of 40-60 ng/ml. Keep in mind that the specific dosage is still a very loose guideline, because people vary widely in their ability to respond to vitamin D.
“Some people may get almost no increase at all with 2,000-or 3,000 IU supplement every day, whereas others may get all the way up to where they need to be with that dose. There’s a huge range of sensitivity. There’s no easy way to handle that for a physician except to measure... If you measure you can tell whether you’re giving enough. The right amount is not some arbitrary number... the right amount is the amount you need in order to get your patient between 40 and 60 ng/ml. Whatever that is, it’s not only the right amount, but it’s the safe amount as well.”
The vitamin D test you’re looking for is called 25(OH)D or 25-hydroxyvitamin D. This is the officially recognized marker of overall D status, and is most strongly associated with overall health. There’s another vitamin D test available, called 1,25-dihydroxy vitamin D (1,25(OH)D). As explained by Dr. Heaney, even though some promote the use of this test, he does not think it’s very useful for determining vitamin D sufficiency. It can however be a useful for assessing your calcium metabolism.
The reason for this, he explains, is because “1,25-dihydroxy D, as it circulates in your body, serves an endocrine function. It communicates between the parathyroid gland and the intestines saying, “Hey, we need more calcium,” and the 1,25-dihydroxy D stimulates the intestinal mucosa to make the transport apparatus, which absorbs calcium out of the food... The blood 1,25-dihydroxy D level is really a measure of calcium status, not vitamin D status.”
Concerns About Vitamin D Toxicity Have Been Overstated
In years past, there were serious concerns about vitamin D toxicity at doses over 2,000 IU’s or so. Another persistent question has been whether or not it might be detrimental to have too high a blood serum level; say a level of 70-100 ng/ml or higher. The Institute of Medicine and various other expert bodies have defined toxicity as hypervitaminosis D (vitamin D toxicity), which consists of excess serum calcium, kidney stones, calcification of the kidney, and related health problems. The good news is, we now know there’s a very wide margin of safety. According to Dr. Heaney, there are no reported cases of elevated serum calcium below 30,000 IU’s of vitamin D per day, and for the most part, there are none below 50,000 IU’s.
“There is, however, a gray zone between 30,000 and 50,000 [IUs of vitamin D per day].But there’s no reason to go above 30,000. I mean, there’s a good margin of safety,” Dr. Heaney says. “Alternatively, if you look at the blood levels of 25-hydroxy vitamin D, there are no recorded cases of vitamin D intoxication at levels below 200 nanograms per milliliter.
We’re talking about 40 to 60 here as the optimal range. There’s no real concern about toxicity until you get up into doses you shouldn’t be taking. Those are almost always associated with either sloppy manufacturing practices or deliberate poisoning. Both kinds of cases have been reported.”
I believe the literature is clear that many of the symptoms associated with vitamin D toxicity are actually related to other nutrient deficiencies—vitamin K2 deficiency specifically. When you take supplemental vitamin D, you increase your body’s need for vitamin K2, so when supplementing with oral vitamin D3, you need to make sure you’re also increasing your K2 and magnesium intake. The biological role of vitamin K2 is to help move calcium into the proper areas in your body, such as your bones and teeth. It also helps remove calcium from areas where it shouldn’t be, such as in your arteries and soft tissues. So vitamin K2 deficiency is actually what produces the symptoms of vitamin D toxicity, which includes inappropriate calcification that can lead to hardening of your arteries.
The Difference Between Disease Prevention and Health Promotion
With all this evidence showing we need far more vitamin D than we're currently getting, why have agencies such as the US Preventive Services Task Force (USPSTF) and the Institute of Medicine (IOM) failed to keep up? Why are they still recommending levels that are so far below ideal? According to Dr. Heaney, there are two main reasons for this discrepancy:
- They're looking for disease prevention rather than health promotion, and the endpoints are very different. The US Preventive Services Task Force, for example, is concerned with the prevention of diseases, and their focus is on what you need to do in order to minimize your risk. "The focus of prevention is not inappropriate for an agency that's concerned with prevention. But that's not the same thing as promotion of nutrition," Dr. Heaney says.
- Lack of study standards for nutritional research is another hurdle. Dr. Heaney notes that there are no standards by which you can decide how to do a study to see if vitamin D lowers blood pressure, or reduces the risk of cancer, for example. He notes: "About 12 months ago, I published a set of guidelines in the journal of Nutrition Reviews,1,2 which set forth a group of five conditions that a clinical study of a nutrient should meet if it's going to answer the question of whether it does any good.
I added to that a set of six criteria for systemic reviews and meta-analyses. The US Preventive Services Task Force, the Institute of Medicine, and several other authoritative bodies have relied on systematic reviews and meta-analyses in order to see if the evidence supported the proposition that vitamin D may reduce the risk of hypertension, cancer, or whatever.
The problem is that if you look at the criteria [I published]... the best of systematic reviews and meta-analyses fail on four of the six criteria. They simply do not meet the criteria needed in order to have an informative study. That’s the second reason why they get null answers; they combine studies, which if adequately understood at the time of their design, would have been said to be null... [they’re] not going to show anything because they aren’t done right.”
Vitamin D—An Inexpensive and Powerful Way to Optimize Your Health
Vitamin D deficiency is extremely common and drives a large number of disease processes, yet it’s quite inexpensive to address, and doing so might make a huge difference in your health. While I recommend getting as much of your vitamin D from sensible sun exposure as possible, you almost certainly will still need a supplement, basically year round.
“We need to keep in mind that under more primitive circumstances, we were getting a lot more [vitamin D] from the sun than we do today. I think if any of you can think back to your own grandparents, you’d realize they spent a lot more time outdoors. They hung their wash out on the line to dry; they mowed the lawn.
They walked to the bus stop or street car stop and they got fresh air. They worked out in the gardens. There was just a lot more outdoor time and sun exposure. People are scared to death now of skin cancer, but nobody was dying of melanoma back in those days. I fear we have a problem that’s been created by the cosmetic industry rather than a real problem for cancer prevention,” Dr. Heaney says.
The January 2015 issue of Nutrition Reviews contains a comprehensive summary of Dr. Heaney's work. To learn a whole lot more about how much vitamin D we typically get from the sun; how much we get from food; the difference between vitamin D2 and vitamin D3, and how it's handled in the body, please read through his paper, Quantifying the Vitamin D Economy in the Body.3