Vitamin D: The Facts
Dr. Robert Heaney examined three lines of evidence, three different views on normal body function, to find out what an optimal blood level of vitamin D would be.5
Since vitamin D is made naturally in the skin with exposure to sunshine with UVB (all year at the equator) without anything blocking it (like sunscreen or clothing), “normal” levels would reflect people who didn’t practice sun avoidance such as East African tribes living traditionally. Masaii and Hadaze tribespeople were found to have average vitamin D status of 115 nmol/L.6
He next looked to pregnancy and the levels that were needed to deliver enough vitamin D from mom to babe through breastmilk.7 Vitamin D is the only supplement that is recommended for babies straight from birth – this is because there is no vitamin D in breastmilk when mom is deficient. When mom’s vitamin D status is approximately 100-150 nmol/L, there is adequate vitamin D in breastmilk that no supplement is required!
The last line of evidence looked at vitamin D’s role in maintaining bone health. There is an interplay between vitamin D, parathyroid hormone and calcium levels. The key feature is the threshold value of vitamin D that will no longer lower parathyroid hormones, the compensatory mechanism for low vitamin D. This happens around 120 nmol/L.8
Risk of several diseases has also been found to be reduced significantly when vitamin D status is above 100 nmol/L including cancer and diabetes, and a reduction in the risk of preterm births. Significantly, there are several not-for profit organizations dedicated to educating the public about vitamin D.9,10,11,12,13,14
While there are some meta-analyses that combine data from randomized controlled trials, and find that vitamin D supplements both improve type 2 diabetes outcomes15 and reduce acute respiratory tract infections16, critics will say there are not enough randomized controlled trials to show that vitamin D has benefits for health outcomes beyond bone.
There are many reasons for this lack of evidence, which is not the same as evidence against vitamin D. The design of these studies may limit the potential to find any benefit by not supplementing at a high enough dose, not taking the dose long enough, or simply because you cannot compare vitamin D supplements to nothing (i.e. no vitamin D at all).17,18 Evidence-based medicine tests the presence of a drug against no drug in randomized controlled trials – you do not naturally have that drug in your system. But vitamin D at some level is going to be in everyone’s system. In nutrition, there is also the complication of interaction with other nutrients – for vitamin D, calcium, phosphorus, vitamin A and vitamin K are all known to interact. It is impossible to ensure that the treated people in a study match the untreated people in these other nutrients.
In fact, the ability of RCTs to accurately assess pharmaceuticals has also been brought into question.19
Given there is extremely little risk associated with vitamin D supplements (see safety section below), the potential benefit far outweighs the risk.
At Pure North, we have identified benefit from vitamin D supplementation on many health outcomes including thyroid function20, improving blood pressure21, improving resilience to depression and anxiety22, improving blood sugar23,24, and insulin control25, reducing inflammation26 and metabolic syndrome.27
International experts on health recommend vitamin D [25(OH)D] levels be in the range of 100 to 175 nmol/L (40 ng/ml – 70 ng/ml in U.S. measurements). To achieve these levels, people need to get adequate sun exposure, eat enough vitamin D rich food, or take supplements.
Research shows that body weight is an important factor.28 The Endocrine Society recognizes that people who are overweight or obese need 2-3 times the amount of vitamin D as a normal weight person to reach the same blood levels.29
As a general rule 35-40 IU of vitamin D per pound of weight is required for a person to achieve an optimal vitamin D range. 30 Dr. Paul Veugelers of the University of Alberta, School of Public Health, crunched the numbers and shows his work in a series of charts that approximate ranges of intake to target blood levels.31
While this provides a good guideline, it is important to remember factors such as height, weight, BMI, age and skin tone all impact these guidelines and therefore a blood test is recommended as the most accurate way to determine a recommended daily intake.
The Recommended Daily Allowance, RDA, for vitamin D is 600 IU/d for people of all sizes from 12 months of age to 70 years. This dose targets a blood level of 50 nmol/L to prevent vitamin D “deficiency.”
Many experts believe this is far too low to reach optimal levels for many reasons: i) The evidence used by Health Canada and the Institute of Medicine took into account vitamin D’s effect on bone health only; ii) Preventing deficiency is not the same as reaching optimal levels for overall health; and iii) The committee made a math error when they calculated this intake and as a result even Health Canada’s recommended intake should be 7-10 times higher! The IOM has acknowledged the mathematical error (see below for details).
*As of February 24, 2021, Health Canada increased the maximum amount for Vitamin D supplements sold over the counter to 2,500 IU/d per dose for adults. The previous maximum was set at 1,000 IU/d per adult dose.
Vitamin D toxicity is exceedingly rare. Dr. Michael Holick, an Endocrinologist and the world’s leading expert on vitamin D, wrote an editorial for a study conducted by the Mayo Clinic where he reviewed the history of vitamin D toxicity. His conclusion: “the evidence is clear that vitamin D toxicity is one of the rarest medical conditions and is typically due to intentional or inadvertent intake of extremely high doses of vitamin D (usually in the range of >50,000-100,000 IU/d for months to years).”32
Dudenkov and colleagues at the Mayo Clinic 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 – almost four times higher than the maximum levels at Pure North.33 The Mayo Clinic is world renowned for the quality of its research and medical care, so those results should be treated with considerable confidence.
The Pure North clinic saw over 44,000 participants in over eight years and did not see even one case of toxicity even though health care practitioners at Pure North routinely recommended doses that exceed the Upper Level (UL) of intake of 4,000 IU/d (recognized by Health Canada as being safe for general consumption).
This study used secondary data from the Pure North program, meaning the data was gathered by the health care practitioners to assess and address the participants’ health concerns. We 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.34 For comparison, 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.
A handful of study participants achieved levels of 300 nmol/L without any evidence of toxicity (toxicity typically means evidence of hypercalciuria or hypercalcemia – in plain language, too much calcium).35
There have been several large population-based studies published in the last few years that further demonstrate the safety of vitamin D blood levels above 250 nmol/L (Pure North’s target is 100-250 nmol/L), and vitamin D doses above the UL. Data from 16 years at an academic medical center in Iowa City included nearly 80,000 patients.36 Less than one percent of patients (only 4) showed symptoms of vitamin D toxicity and these patients were accidently taking doses of vitamin D over 100,000 IU/d.
Twenty international experts on vitamin D published a comprehensive review of vitamin D deficiency, health benefits of supplementation, blood levels and recommendations.37 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.
The Alberta Medical Association produces practice guidelines called “Toward Optimized Practice (TOP)” which is an AMA service for Alberta physicians to “implement evidence-based practices to enhance the care of their patients”. One of TOP’s resources for physicians is a series of “Clinical Practice Guidelines”.
Toward Optimized Practice Guidelines for Alberta Physicians state:38
- Testing for vitamin D should not be necessary for most patients because “Vitamin D supplementation for this general population should be recommended without a need to screen or monitor vitamin D levels”. In other words, a deficiency of vitamin D in the general population is assumed to exist without the routine need to test for it.
- The best test for vitamin D sufficiency is blood serum level (not intake) because of variations in how vitamin D is consumed and processed by individual patients.
- Vitamin D toxicity is very rare, and is defined as a blood serum level consistently above 500 nmol/L.
What is clear is that vitamin D blood levels which were targeted by Pure North, of 100 to 250 nmol/L, are safe and may provide a number of health benefits.
In 2010, the then IOM (now named National Academy) released a study that recommended 600 to 800 International Units (IU) of vitamin D per day for most adults to counter vitamin D deficiency. Since then, scientists from the University of Alberta, University of California San Diego and Creighton University have taken another look.
These scientists took a critical eye to the methodologies employed by the IOM panel to calculate the RDA. They discovered mathematical errors. A letter detailing the errors was first published in the scientific journal Nutrients in 2014.39 The assertions in that letter were further tested by other scientists, and confirmed in a second article in Nutrients in 2015.40 These are not new criticisms. In fact there were several experts in the field that published papers that detailed the faulty reasoning of the 2011 IOM committee.41,42,43,44,45,46
These peer reviews found that the IOM’s recommendation of 600-800 IU was about one-tenth of what it should be. Instead, the reviewing scientists found that the evidence pointed to an optimal daily intake of 7,000 IU of vitamin D per day.47
The IOM panel – predictably – first fiercely defended their work, denied their error, and refused to change the recommendations. After considerable pressure, with numerous publications and reports sent directly to Health Canada and the IOM, they did undertake a two-part review. In Phase I, they asked whether errors had been made. In Phase II, they asked how those errors affected the ultimate recommendation.
How can that be? The answer: the now-named National Academy remarkably claims that the IOM did not use the study to formulate their advice to government. Therefore, the study’s accuracy is irrelevant. Instead, the Academy says the recommendations were determined by “expert opinion” which turned out to be the consensus opinion of the IOM committee panel. In fact, this confirms the suspicions of the scientists that questioned their conclusions from the beginning.
One more thing: two of the members of the original IOM committee that established the RDA in 2011 also counted for two of the four members of Panel II – the one that decided whether the errors influenced the RDA: Dr. A. Catharine Ross, a Professor at Penn State University with an interest in vitamin A, who chaired the 2010 group that undertook the initial study; and Dr. Sue Shapses, a Professor at Rutgers University with an interest in obesity and osteoporosis. It is a clear conflict of interest to be engaged in both the initial study that was found to be in error, and the panel that chose to disregard the corrected conclusions. One wonders if professional hubris played a role in rejecting the corrected outcomes.
The logic here is worthy of Alice in Wonderland, except that it deals with the most serious matter of Canadians’ health. The end result is that Canadians are not getting the vitamin D they need to support their health.