How safe is vitamin D?

At Pure North, we are sometimes asked if our confidence in the benefits and safety of vitamin D is well founded in science. The answer is yes.

Vitamin D safety has been proven once again with a study published on April 13, 2017 in the Journal of Dermato-Endocrinology.

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Vitamin D safety has been proven once again with a study published on April 13, 2017 in the Journal of Dermato-Endocrinology.

Source: Journal of Dermato-Endocrinology

Endocrinologists are concerned about the chemistry of the body, and dermatology is the science of the skin. vitamin D is naturally made in the skin from UVB rays or can be obtained by taking supplements (only a small amount comes from food). Endocrinologists are interested in how vitamin D influences the body processes that affect our health.

Vitamin D is in every cell

More and more research is showing how vitamin D interacts with our body. Nearly every cell has a vitamin D receptor (VDR). Vitamin D is necessary for many cellular functions including skeletal strength, immune system fitness, developmental and cardiovascular health, to name just a few. Adequate vitamin D is also important for pre-natal health and reducing pre-mature births.

A low level of vitamin D increases the risks of diseases including auto-immune disorders, diabetes, cardiovascular disease and cancer.

These benefits have been well studied. We know vitamin D is good for us, and we know most of us don’t get enough.

We wear sunscreen and stay out of direct sunlight. As we get older our bodies process UV rays into vitamin D less efficiently. If we are overweight or obese, our bodies require more vitamin D. Our food contains very little vitamin D so we don’t get much that way.

Supplements are necessary. The question is, how much is enough? And how much is too much?

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Focus on the blood level, not the intake

The most important thing to remember is that the best measurement of vitamin D in your body is not how much you take in, but how much is in your blood – a measurement called serum 25(OH)D concentration.

Since different people absorb and process vitamin D differently, it is not a question of how much you take in, but how much is in your blood.


Since different people absorb and process vitamin D differently, it is not a question of how much you take in, but how much is in your blood.

Their study examines vitamin D supplementation of up to 15,000 International Units (IU) per day, which is more than most people take and higher than Health Canada recommends.

The objective was not to examine intake, however, but to measure and observe blood serum levels.

They used data collected by a medical clinic. The goal in the clinic is for patients to a blood serum 25(OH)D level of 100 nmol/L (nanomoles per litre of blood).

The Endocrine Society Practice Guidelines recommend a blood serum level of 100 to 150 nmol/L for maximum bone and muscle health. 100 nmol/L is within the range accepted by the Institute of Medicine (IOM), and the IOM range is accepted by Health Canada.

How much vitamin D did subjects need to take in order to attain a blood concentration of 100 nmol/L? Further, would taking that amount of vitamin D cause any negative side effects?

This study observed that the amount of vitamin D required to achieve 100 nmol/L was between 6,000 and 8,000 IU/day for most people, and two to three times more than that for overweight and obese individuals.

And yet, Health Canada and the IOM claim that 4,000 IU/day is the Upper Tolerable Limit (the amount of supplement you can take without risking side effects).

In other words, the amount of vitamin D required to meet the target level of blood serum is higher than the amount of vitamin D supplementation that Health Canada recommends.

Many researchers feel the Health Canada guideline is too low. But is it safe to take more and achieve a higher blood serum level?

15,000 IU is the equivalent of an adult in a bathing suit exposed to an amount of sunlight that would cause a slight pinkness to the skin 24 hours later.

The Endocrine Society Practice Guidelines recommend that up to 10,000 IU as safe for adults. This study wanted to examine if more than 4,000 IU/day is, in fact, safe.

How high is too high?

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The Endocrine Society reports that a blood serum level up to 250 nmol/L is not associated with toxicity. In fact, toxicity is usually not observed until a level of 500 nmol/L.

Source: Journal of Dermato-Endocrinology

This study showed results consistent with that analysis.

Some study participants achieved levels of 300 nmol/L without any symptomatic evidence of toxicity (toxicity typically means evidence of hypercalciuria or hypercalcemia – in plain language, too much calcium).


A study conducted for the Mayo Clinic by Dr. Daniel V. Dudenkov and colleagues over ten years (2002-2011) looked at over 20,000 measurements of blood serum vitamin D, and found only one symptomatic case of toxicity, and that was at a level of over 900 nmol/L – more than three times higher than the target levels at Pure North. The Mayo Clinic is world renowned for the quality of its research and medical care, so those results should be treated with considerable confidence.


Twenty international experts on vitamin D published a comprehensive review of vitamin D deficiency, health benefits of supplementation, blood levels and recommendations. Published in the Journal of Steroid Biochemistry and Molecular Biology, the group concluded that there is a worldwide deficiency in vitamin D levels and that health care costs could be significantly diminished simply with an improvement in vitamin D sufficiency. This study concluded that a level of 250 nmol/L for children and adults is completely safe, and up to at least 375 nmol/L would be required before seeing any signs of toxicity.

While the level of vitamin D required to indicate possible side-effects varies in these studies, one thing is completely consistent: the safe level of vitamin D in the blood is considerably higher than that recommended at Pure North, so participants should feel confident that their treatment is both safe and effective.


Why do overweight and obese individuals require more? There are several possible reasons.

Vitamin D is fat soluble, so it may be distributed more widely through the body into fat reserves.

Obesity is associated with chronic inflammation, and vitamin D is a powerful anti-inflammatory agent, so more may be required by the bodies of the obese.

Further, vitamin D is a modulator of the gut microbiome, which is strongly influenced by diet, and the different microbia in the gastro-intestinal system of the obese could reduce the absorption of vitamin D.

Whatever the reason, those who are overweight need more vitamin D to achieve ideal blood serum levels. That’s why it is important to focus on blood serum levels, not intake.

Patients with gastro-intestinal ailments such as Crohn’s disease or IBD may also be vitamin D deficient due to absorption issues.

There is considerable debate amongst doctors and researchers about the correct Recommended Daily Allowance of vitamin D.

This study did not try to establish the ideal intake, but did confirm the safety of blood serum levels up to 300 nmol/L and intakes of vitamin D up to 15,000 IU/day.

Every person is different, but the study results suggest that intakes of 6,000 to 8,000 IU/day are needed to achieve a blood serum level of 100 nmol/L. That is a level supported by considerable research as a reasonable level for healthy physiology and disease prevention.

What is Pure North’s recommendation?

At Pure North, we assess each participant individually to establish a target blood serum level, and to monitor how much vitamin D should be taken in supplement form to achieve that level.

We never allow a participant to reach a blood serum level that is too high, even given the evidence in this study that higher levels are still safe. Typically, if a Pure North participant nears 250 nmol/L, we will reduce vitamin D intake to maintain a level at or below 250 nmol/L. This study demonstrates that 250 nmol/L is well within the range shown to be safe.

We want our participants to feel better and live longer. We believe that vitamin D is an important part of the equation to achieve that goal.

Research confirms time and again that Pure North’s recommended levels of vitamin D supplementation are safe and effective.

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