Meanwhile, statistics suggest that between 40-50% of otherwise healthy adults and children don’t have enough vitamin D.
In fact, the past few years have seen a worldwide increase in rickets, a vitamin D deficiency usually seen in malnourished children — even in industrialized countries!
The good news: Health care providers are aware of this research and the risks associated with low vitamin D levels.
What’s potentially more troubling is their response.
Many doctors routinely prescribe high levels of vitamin D supplements, with doses ranging from 2000-10,000 IU (International Units) per day, up to 50,000 IU per week, and sometimes more.
Vitamin D obviously supports human health. But why aren’t we addressing the underlying reasons that our D levels are so routinely low?
And how safe is long-term, high dose vitamin D supplementation, really?
Are we over-D-osing ourselves?
What is vitamin D and how is it made?
The term “vitamin D” refers to a group of fat-soluble compounds that serve as pre-hormones, or hormone precursors, to the active form of vitamin D, called calcitriol.
Among the more well known forms of vitamin D is vitamin D3 (cholecalciferol), found in fish, egg yolks, and cheese, and synthesized in the skin of humans and animals.
Another common form, vitamin D2 (ergocalciferol), is synthesized by plants, such as mushrooms, and is the form most often used to fortify foods such as milk.
We make vitamin D in our skin when we get out in the sun — more precisely, when our skin is exposed to ultraviolet-B radiation (UVB).
This initial form of vitamin D, called 7-dehydrocholesterol, then travels to the liver, where it is converted into another slightly more active form of vitamin D called 25-hydroxyvitamin D.
This is the form of the vitamin that doctors are testing when looking for deficiency.
When vitamin D leaves the liver, it travels to the kidneys where it is converted once more into the highly metabolically active form of vitamin D called calcitriol, or 1,25 dihydroxyvitamin D.
This is no longer considered a vitamin but rather, a steroid hormone. (You may be familiar with other steroid hormones such as estrogen, testosterone, and cortisol).
Vitamin D’s role in the body
As the name of vitamin D’s active form, calcitriol, suggests, this micronutrient helps regulate calcium and other minerals in our bodies. Calcitriol increases calcium absorption from food in our digestive tract.
If we need more calcium, our kidneys can produce more of the active form of vitamin D, which raises our calcium levels by increasing the amount we absorb from our food.
Before the recent interest in vitamin D, it was thought that only a few select organs of our body had receptors for vitamin D, called Vitamin D Receptors, or VDRs.
However, recent research suggests that nearly every cell of our body has receptors for vitamin D, indicating a much more potent role for this vitamin than we previously recognized.
This new information has helped us discover that vitamin D also influences our immune system and helps in cell differentiation, blood pressure regulation, insulin secretion, and more.
This brings us back to our original question: What does a vitamin D deficiency mean? What does it signal — in a broader sense — about what might have gone wrong in our bodily processes?
The D-eficiency debate
25-hydroxyvitamin D, the form of vitamin D largely produced by the liver, is generally accepted as the most reliable marker to assess one’s vitamin D status.
However, that’s where the agreement ends. Scientists can’t even agree on the optimal reference range for vitamin D.
True vitamin D deficiency — the kind that will cause bone abnormalities such as rickets and osteomalacia — occurs at levels below 25 ng/mL in blood.
Some researchers believe a more optimal range is anywhere between 50 – 80 ng/mL. But there’s no universal consensus.
In 2010, the National Institute of Health (US) set the Recommended Dietary Allowance for vitamin D at 600 IUs daily for infants, children, and adults up to 70 years of age. This is an increase from their previous recommendation of 200 IUs daily.
While this increase may seem substantial, some people claim that it doesn’t go far enough and could be “disastrous” to health.
We’ll consider that later in this article.
Sunny days… or not?
According to the National Institutes of Health Office of Dietary Supplements, we can easily meet our body’s requirements for vitamin D simply by getting enough sunshine.
Exposing 30% of our unprotected skin (i.e. non-sunscreen coated, unclothed skin) for five to thirty minutes between the hours of 10 a.m. and 3 p.m., three times a week, should do it.
But given the number of us suffering from sub-optimal levels of vitamin D — even in latitudes with high sun exposure — you have to wonder if that recommendation is accurate.
And for those of us who live north of the 49th parallel — well, let’s just say that we won’t be exposing 30% of our unprotected skin very often in the winter.
If your levels are low, should you supplement?
It’s clear that vitamin D plays a number of important roles in the body and that vitamin D deficiency can hurt you.
Some studies suggest that the lower one’s vitamin D level, the higher the risk of all-cause mortality.
On the other hand, studies also indicate that the risk of overall mortality actually rises once vitamin D levels exceed ~40 ng/mL.
And overall, we just don’t have solid scientific evidence about the long-term safety of high dose vitamin D supplementation.
Perhaps, before we start swallowing too many pills, we need to evaluate what we are doing. After all, medical science has been wrong before.
To get a better understanding of the issues, let’s explore some important relationships between vitamin D and other key nutrients.
Vitamin D and calcium
One potential risk of excessively high dose vitamin D is toxicity causing hypercalcemia, or high levels of calcium in the blood.
It works to kill rats. One form of rodenticide is essentially a toxic dose of vitamin D — enough to cause the soft tissues to calcify and kill the animal.
However, hypercalcemia rarely appears without supra-physiological doses of vitamin D, which in humans would be somewhere in the range of 30,000-40,000 IUs daily.
Most people who supplement with vitamin D don’t take anywhere near that amount.
Still, that doesn’t necessarily mean the dose they are taking is safe.
Calcium levels in the body are so tightly regulated that abnormalities won’t always show up in blood serum tests. But they may appear in other ways.
One of these is hypercalcuria — otherwise known as calcium kidney stones.
Hypercalcuria occurs when the body tries to rid itself of excess calcium by excreting it, via the kidneys. Based on this relationship, some researchers suggest that high levels of vitamin D supplementation may lead to kidney stones.
Indeed, one study demonstrated that nursing home residents taking 5,000 IU of vitamin D for six months showed an increased urinary calcium/creatinine ratio, suggesting that excess calcium was coming out in the urine — likely because there was too much in their bodies.
On the other hand, another recent study found that among subject with vitamin D levels ranging from 20 – 100 ng/mL, there was no difference in the occurrence of kidney stones.
So the verdict isn’t clear.
But kidney stones are not the only risk of too much calcium.
If the body can’t regulate calcium levels, the mineral may deposit itself throughout the soft tissues of the body, including the arteries. And unfortunately, some studies suggest that this is a real possibility when vitamin D levels become too high.
Three studies in particular have demonstrated increased arterial calcification in animal models with a range of vitamin D intake.
And other studies suggest that too much vitamin D could also hurt human cardiovascular function.
You know, the mere possibility that high-dose vitamin D supplementation could increase calcium levels in the soft tissues of the body (e.g. the arteries) should raise serious questions about the practice of supplementing this way.
Especially considering the prevalence of heart disease in our society.
So by now, you may be ready to toss your vitamin D supplement in the garbage.
But before you do, again: We really need to consider why our vitamin D levels seem so inadequate that we’re tempted to supplement in the first place.
Recall: Vitamin D and calcium exist in a delicate balance.
So maybe, just maybe, vitamin D levels are low because calcium levels are already too high.
And through a negative feedback loop, the body suppresses vitamin D production and/or conversion to minimize further increases in calcium.
Why might our calcium levels be too high? Possibilities include magnesium deficiency, pH imbalance, protein deficiency, liver dysfunction, and more.
In other words — maybe the oil is low because there is an underlying problem, not just because the car guzzles oil.
Let’s take a closer look at some possible interactions.
Vitamin D and vitamin K
The “K” in vitamin K comes from the German koagulation. Coagulation refers to the process of blood clot formation. This should hint to you that vitamin K plays a crucial role in the body’s blood clotting pathway.
Put simply, vitamin K allows the body to use calcium to perform its clotting function.
If vitamin K is low, the body can’t use calcium in this way, and therefore, cannot clot.
Besides its role in clotting, Vitamin K also helps to form and maintain our bones and teeth.
It does so by activating a specific protein called osteocalcin that helps the body use calcium and deposit it where it belongs.
In other words, there is a very potent calcium-vitamin K connection in that vitamin K helps the body use calcium properly. And if we’re deficient in vitamin K, calcium levels can build up and deposit themselves in our soft tissues.
People who are low in vitamin K are more likely to suffer from atherosclerosis, or calcification of the arteries.
And those with a high vitamin K intake (especially vitamin K2) seem to have less calcification of their arteries.
In fact, research in rats has shown that supplementing with vitamin K2 (but not K1) not only inhibits arterial calcification, it can also remove 30-50% of the calcium that has already been deposited.
Unfortunately, this magic effect has not been shown in humans as yet.
Hopefully by now, you can see the delicate dance that’s going on. Vitamin D increases calcium levels in the body. Vitamin K helps the body use calcium.
So if one were to supplement with high-dose vitamin D in the presence of vitamin K deficiency, the long-term results could be disastrous.
Vitamin D and magnesium
Magnesium is an important mineral involved in over 300 different processes in the body, including the ability to make and use ATP, the body’s main form of energy.
Of those 300 roles, magnesium aids in a handful of activities related to vitamin D production and use. In particular, it seems to modulate the sensitivity of our tissues to vitamin D.
Not only does magnesium play an important role in proper Vitamin D activity and function, but crucially, it also helps to maintain calcium balance.
At least half of the population fails to meet the Recommended Dietary Allowance for magnesium. This may be because soil levels of magnesium have fallen considerably in the past 50 years, making it harder to meet our needs.
Because magnesium is used in vitamin D metabolism, some researchers theorize that supplementing with high levels of vitamin D could cause an even greater magnesium deficiency in an already deficient population.
Interestingly, a relatively recent study demonstrated a strong correlation between magnesium and vitamin D deficiency.
This study showed that magnesium supplementation, taken along with vitamin D supplementation, was more effective at correcting a vitamin D deficiency than vitamin D supplementation alone.
Simply by increasing magnesium intake, we may decrease mortality related to vitamin D deficiency — without taking any extra vitamin D.
But beyond vitamin D’s relationship to magnesium is magnesium’s relationship to calcium. And in some ways, these two minerals have opposite effects.
For example, calcium stimulates muscle contraction while magnesium promotes muscle relaxation. Calcium boosts platelet activation and clotting, while magnesium inhibits them.
Contrary to popular belief, the individual level of either of these minerals may be less important than the balance between the two.
Too much calcium together with a magnesium deficiency could cause problems like increased calcium deposits in the arteries. Meanwhile, bumping up magnesium can prevent calcification of the arteries.
But what if you’re low in magnesium and decide to supplement with vitamin D?
There could be many negative consequences, including — you guessed it — calcium deposits in the arteries.
Vitamin D and vitamin A
Besides its delicate interactions with calcium and vitamin K, vitamin D also relates to vitamin A in our bodies.
The term “vitamin A” refers to another group of fat-soluble compounds which aid growth and development, reproduction, immune system function, eyesight, skin health, and gene expression.
Because fat-soluble vitamins can be stored in the body, they can reach toxic levels.
And here’s something interesting: It turns out that vitamin A can prevent vitamin D toxicity, and vice versa.
What this means is that if you’re deficient in vitamin A, high doses of vitamin D could cause problems.
And the lower your vitamin A status, the more toxic excess vitamin D becomes.
Meanwhile, some studies suggest that increasing vitamin A can reduce the calcium buildup that tends to go along with higher levels of vitamin D.
It could also protect against the pathological calcification effects of too much vitamin D supplementation.
Here’s the bottom line — it’s about balance
By now, the point should be clear: In the presence of other deficiencies, we should be careful about supplementing with high doses of vitamin D.
With studies suggesting that up to 35% of our population may be sub-clinically deficient in vitamin K, and a body of mounting evidence exploring the synergistic interplay between vitamin K and vitamin D with calcium homeostasis, bone formation, and arterial calcification, we need to take this warning seriously.
In fact, one study suggests that vitamin D supplementation may actually contribute to vitamin K deficiency (and in turn to bone loss and calcification of soft tissues).
The researchers recommended supplementing vitamins A and K simultaneously with vitamin D to improve the therapeutic effect of vitamin D while decreasing potential unwanted side effects of vitamin D taken alone.
The most worrisome of these is the effect of too much vitamin D on calcification of the cardiovascular system.
Cardiovascular disease is already the number one killer in industrialized nations. We don’t need to add to the risks of developing it.
Take D with care
As much as we think we know about the human body, we still have more to learn.
For instance, just when we thought we had human anatomy all figured out, a “new” ligament appeared in the knee. (Of course, it had been there all along.)
And when it comes to human physiology and biochemistry, as well as the role that nutrition and individual nutrients play in our bodies, we know even less.
The point of this article is not to frighten you away from vitamin D supplements.
Vitamin D deficiency is a real phenomenon and a real risk to health, so we need to ensure that we’re getting enough of this important nutrient.
At the same time, we also need to:
question the possible long-term consequences of high dose vitamin D supplementation in isolation;
consider the role of other key nutrients that work together with vitamin D; and
always look for the underlying cause of any deficiency symptoms.
What should you do?
1. Get enough vitamin D… but not too much.
Doses of around 1,000 IUs per day — even as high as 2,000 IUs a day in the winter months when you’re not exposed to much sunlight — are likely safe. Especially when other key nutrients are included, such as vitamin K, vitamin A, and magnesium. You can ensure you are getting enough of these by taking a quality multi-vitamin.
Avoid vitamin over-dosing. While it’s clear that the previous recommendation of 200 IUs a day is probably too low, until more conclusive research on long term high-dose vitamin D supplementation has been completed, you should avoid taking too much.
Get outside. Yeah, it’s not a perfect system, especially in winter months. But sunlight is still the best way for our bodies to make and regulate vitamin D.
2. Support vitamin D’s work
Remember that other nutrients act together with vitamin D. Consume a wide variety of minimally processed foods to help get vitamin D’s nutritional colleagues such as magnesium, vitamin A, and vitamin K.
Eat your greens and fermented foods. Dark leafy greens — such as kale, spinach, or Swiss chard — are good sources of vitamin K1. They’re also high in dietary magnesium. Fermented veggies such as sauerkraut along with eggs, meats (especially organ meats such as liver) and fermented/aged cheeses are good sources of vitamin K2.
Eat the rainbow. The carotenoid form of vitamin A is found in colorful fruits and veggies. Eggs, butter, full-fat dairy (such as cheese) and organ meats are also great sources of the active retinol form of vitamin A.
Keep your intestinal flora happy and healthy. Vitamin K conversion happens in the GI tract. So eat plenty of fermented foods and prebiotic fiber, consider a probiotic supplement, and avoid antibiotics unless absolutely necessary (research has found that broad-spectrum antibiotics can reduce K production by up to 75%).
Review all medications and supplements with your doctor and/or pharmacist. Many medications, such as corticosteroids like Prednisone, weight loss drugs like Orlistat, cholesterol-blocking drugs like statins, and/or high blood pressure drugs like thiazide diuretics can disrupt the delicate balance of vitamin and mineral regulation in the body. Make sure you know all the side effects and interactions of any medications (or “healthy” supplements) you are taking.
Eat, move, and live…better.
The health and fitness world can sometimes be a confusing place. But it doesn’t have to be.