Why do I need to take vitamin D supplements?
Vitamin D is a hormone that is known for its role in bone health, but is also important for making sure your muscles, heart, lungs and brain work well, and for your immune system, making sure your body can fight off colds and infection.1 Sunlight is the natural source for vitamin D, but most Canadians are deficient.
Virtually every North American suffers from insufficient vitamin D because of limited sun exposure and use of sunscreen which blocks vitamin D production.Very little vitamin D is found in food. With Canada’s northern latitude and proximity to the sun, Canadians aren’t able to generate vitamin D in the winter months (late October through early March). The angle of the sun in the winter months means no matter how many sunny days there are, the vitamin D-soaked UVB rays aren’t powerful enough for people to make vitamin D from the sun’s rays.
The Canadian Health Measures Survey, a national representation of population health, has found that 32% of Canadians are vitamin D deficient,3 a rate that has been steadily increasing. Average vitamin D status levels, measured by 25-hydroxyvitamin D [25(OH)D] concentrations, have decreased from 63.1 nmol/L in 2011 to 59.4 nmol/L in 2015.4 Study after study shows that Canadians are typically vitamin D insufficient or deficient. Some provincial health services no longer cover vitamin D testing because doctors are advised to assume everyone is low in vitamin D.
What are “Optimal” vitamin D levels?
The absence of disease does not mean the same as in good health. Similarly, the absence of deficiency is not the same as optimal levels. Optimal levels are those that support normal physiological function – they support the proper function of our bodies.
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.9-14
While there are some meta-analyses that combine data from randomized controlled trials, and find that vitamin D supplements both improve type 2 diabetes outcomes20 and reduce acute respiratory tract infections,21 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 function,20 improving blood pressure,21 improving resilience to depression and anxiety,22 improving blood sugar23, 24 and insulin control,25 reducing inflammation26 and metabolic syndrome.27
How much Vitamin D do I need to take?
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.13 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.30
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.
Why is this different from what Health Canada recommends?
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).
Are vitamin D supplements safe?
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).”31
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.32 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 has seen over 44,000 participants in over eight years and has not seen even one case of toxicity even though health care practitioners at Pure North routinely recommend 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.33 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).33
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.34 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.35 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:36
- 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 (Pure North participants are targeted to less than half that level, at less than 250 nmol/L)
What is clear is that vitamin D blood levels targeted by Pure North, of 100 to 250 nmol/L, are safe and may provide a number of health benefits.
Vitamin D Recommendations were made in Error
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 2014.37 The assertions in that letter were further tested by other scientists, and confirmed in a second article in Nutrients in 2015.38 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.39-44
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.30
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.
Phase I confirmed that, in fact, two material errors of calculation had been made.45 Phase II claimed, however, that these errors of fact had not influenced the recommendations.46
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.ent for his workers and their families led to his recognition of the role that vitamins and other nutrients play in their health and welfare. It didn’t take long for him to realize the impact these services could have on a larger population, that’s why Allan created the Pure North S’Energy Foundation in 2007. Allan’s presence is reflected in Pure North’s research driven core, the ambition to create significant government policy change and the motivation for everyone to live healthier and more fulfilling lives. Pure North’s goal is to prevent chronic disease using research based nutrients.
Political Studies and President of St. Thomas More College, University of Saskatchewan. He is President Emeritus of St, Mary’s University, Calgary, and a former Chair, Department of Political Science, University of Waterloo. He is an award winning professor whose areas of academic expertise include public policy and administration, and Canadian political economy.
- Wang H, Chen W, Li D, Yin X, Zhang X, Olsen N, Zheng SG. Vitamin D and chronic disease. Aging and Disease 2017; 8: 346-53. http://www.aginganddisease.org/EN/10.14336/AD.2016.1021
- Martineau AR, Jolliffe DA, Hooper RL, Greenberg L, Aloia JF, Bergman P, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systemic review and meta-analysis of individual participant data. British Medical Journal 2017; 356: i6583. http://www.bmj.com/content/356/bmj.i6583
- Janz T, Pearson C. Vitamin D blood levels of Canadians. Statistics Canada Catalogue no. 82-624-X. http://www.statcan.gc.ca/pub/82-624-x/2013001/article/11727-eng.htm
- Nutritional status of the household population, by sex and age group. Table 117-0018. http://www5.statcan.gc.ca/cansim/a26?lang=eng&retrLang=eng&id=1170018&&pattern=&stByVal=1&p1=1&p2=31&tabMode=dataTable&csid=
- Heaney RP. Toward a physiological referent for the vitamin D requirement. Journal of Endocrinological Investigation 2014; 37: 1127-30. https://link.springer.com/article/10.1007/s40618-014-0190-6
- Luxwolda MF, Kuipers RS, Kema IP, van der Veer E, Dijck-Brouwer DA, Muskiet FA. Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/L. British Journal of Nutrition 108: 1557-61. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/traditionally-living-populations-in-east-africa-have-a-mean-serum-25hydroxyvitamin-d-concentration-of-115-nmoll/6188564A01361C5CF5F196229430E475
- Hollis BW, Wagner CL, Howard CR, Ebeling M, Shary JR, et al. Maternal versus infant vitamin D supplementation during lactation: a randomized controlled trial. Pediatrics 2015; 136: 625-34. http://pediatrics.aappublications.org/content/136/4/625
- Ginde AA, Wolfe P, Camargo CA, Schwartz RS (2012) Defining vitamin D status by secondary hyperparathyroidism in the US population. J Endocrinol Invest 35:42–48. https://link.springer.com/article/10.3275/7742
- Grant WB, Whiting SJ, Schwalfenberg GK, Genuis SJ, Kimball SM. Estimated economic benefit of increasing 25-hydroxyvitmain D concentrations of Canadians to or above 100 nmol/L. Dermato-Endocrinology 2016; 8: e1248324. http://www.tandfonline.com/doi/abs/10.1080/19381980.2016.1248324
- Lower Disease Incidence with Vitamin D levels 40-60 ng/mL. https://grassrootshealth.net/project/general-health/
- GrassrootsHealth Documentation. https://grassrootshealth.net/documentation/
- McDonnell SL, Baggerly C, French CB, Baggerly LL, Garland CF, Gorham ED, Lappe JM, Heaney RP. Serum 25-hydroxyvitamin D concentrations ≥40 ng/ml are associated with >65% lower cancer risk: Pooled analysis of randomized trial and prospective cohort study. PLoS One 2016; 11: e0152441. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0152441
- Vitamin D Council. Position statement on supplementation, blood levels and sun exposure. https://www.vitamindcouncil.org/for-health-professionals-position-statement-on-supplementation-blood-levels-and-sun-exposure/
- Vitamin D Society. Vitamin D Health Benefits. http://www.vitamindsociety.org/benefits.php
- Mirhosseini N, Vatanparast H, Mzidi M, Kimball SM. The effect of improved serum 25-hydroxyvitamin D status on glycemic control in diabetic patients: a meta-analysis. Journal of Clinical Endocrinology and Metabolism 2017; 102: 3097-110. https://academic.oup.com/jcem/article-abstract/102/9/3097/3920535?redirectedFrom=fulltext
- Martineau AR, Jolliffee DA, Hooper RL, Greenberg L, Aloia JF, Bergman P, et al. Vitamin D supplementation to prevent acute respiratory tract infections: a systematic review and meta-analysis of individual participant data. British Medical Journal 2017; 356: i6583. http://www.bmj.com/content/356/bmj.i6583
- Blumberg J, Heaney RP, Huncharek M, Scholl T, Stampfer M, Vieth R, Weaver CM, Zeisel SH. Evidence-based criteria in the nutritional context. Nutrition Reviews 2010; 68: 478-84. http://onlinelibrary.wiley.com/doi/10.1111/j.1753-4887.2010.00307.x/full
- Thomas LE. How evidence-based medicine biases physicians against nutrition. Medical Hypotheses 81: 1116-9. http://www.medical-hypotheses.com/article/S0306-9877(13)00489-1/fulltext
- Bothwell LE, Greene JA, Podolsky SH, Jones DS. Assessing the gold standard- Lessons from the history of RCTs. The New England Journal of Medicine 2016; 374: 2175-81. http://www.nejm.org/doi/full/10.1056/NEJMms1604593
- Mirhosseini N, Brunel L, Muscogiuri G, Kimball S. Physiological serum 25-hydroxyvitamin D concentrations are associated with improved thyroid function – observations from a community-based program. Endocrine 2017; 58: 563-73. https://link.springer.com/article/10.1007/s12020-017-1450-y
- Mirhosseini N, Vatanparast, Kimball S. The association between serum 25(OH)D status and blood pressure in participants of a community-based program taking vitamin D supplements. Nutrients 2017; 9: E1244. http://www.mdpi.com/2072-6643/9/11/1244
- Kimball SM, Mirhosseini N, Rucklidge J. Database analysis of depression and anxiety in a community sample – response to a micronutrient intervention. Nutrients 2018 [Submitted].
- Kimball SM, Emery JCH, Lewanczuk RZ. Effect of vitamin and mineral supplementation on glycemic status: results from a community-based program. Journal of Clinical and Translational Endocrinology 2017; 10: 28-35. http://www.jctejournal.com/article/S2214-6237(17)30075-3/fulltext
- Munasinghe LL, Mastroeni MF, Mastroeni SSBS, Loehr SA, Ekwaru JP, Veugelers PJ. The association of serum 25-hydroxyvitamin D concentrations and elevated glycated hemoglobin values: a longitudinal study of non-diabetic participants of a preventive health program. Nutrients 2017; 9:E640. http://www.mdpi.com/2072-6643/9/7/640
- Pham TM, Ekwaru JP, Loehr SA, Veugelers PJ. The relationship of serum 25-hydroxyvitamin D and insulin resistance among nondiabetic Canadians: a longitudinal analysis of participants of a preventive health program. PLOS One 2016; 10: e0141081. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141081
- Mastroeni SSBS, Munasinghe LL, Pham TM, Loehr SA, Ekwaru JP, Mastroeni MF, Veugelers PJ. The effect of serum 25-hydroxyvitamin D concentrations on elevated serum C-reactive protein concentrations in normal weight, overweight and obese participants of a preventive health program. Nutrients 2016; 8: 696. http://www.mdpi.com/2072-6643/8/11/696
- Pham TM, Ekwaru JP, Setayeshgar S, Veugelers PJ. The effect of changing serum 25-hydroxyvitamin D concentrations on metabolic syndrome: a longitudinal analysis of participants of a preventive health program. Nutrients 2015; 7: 7271-84. http://www.mdpi.com/2072-6643/7/9/5338
- Ekwaru JP, Zwicker JD, Holick MF, Giovannucci E, Veugelers PJ. The importance of body weight for the dose response relationship of oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers. PLOS One 2014; 9: e111265. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111265
- The Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology and Metabolism 2011; 96: 1911-30. https://academic.oup.com/jcem/article/96/7/1911/2833671?searchresult=1
- Veugelers PJ, Pham T-M, Ekwaru JP. Optimal vitamin D supplementation doses that minimize the risk for both low and high serum 25-hydroxyvitamin D concentrations in the general population. Nutrients 2015, 7: 10189-208. http://www.mdpi.com/2072-6643/7/12/5527
- Holick MF. Vitamin D is not as toxic as was once thought: a historical and an up-to-date perspective. Mayo Clinic Proceedings 2015; 90: 561-4. http://www.mayoclinicproceedings.org/article/S0025-6196(15)00244-X/abstract
- Dudenkov DV, Yawn BP, Oberhelman SS, Fischer PR, Singh RJ, Cha SS, Maxson JA, Quigg SM, Thacher TD. Changing incidence of serum 25-hydroxyvitamin D values above 50 ng/mL: a 10-year population-based study. Mayo Clinic Proceedings 2015; 90: 577-86. http://www.mayoclinicproceedings.org/article/S0025-6196(15)00185-8/fulltext
- Kimball SM, Mirhosseini N, Holick MF. Evaluation of vitamin D3 intakes up to 15,000 IU/d and serum 25-hydroxyvitamin D concentrations up to 300 nmol/L on calcium metabolism in a community setting. Dermato-Endocrinology 2017; 9:e1300213. http://www.tandfonline.com/doi/full/10.1080/19381980.2017.1300213
- Lee JP, Tansey M, Jetton JG, Krasowski MD. Vitamin D toxicity: a 16-year retrospective study at an academic medical centre. Laboratory Medicine 2018 [epub ahead of print]. https://academic.oup.com/labmed/advance-article-abstract/doi/10.1093/labmed/lmx077/4807321?redirectedFrom=fulltext
- Pludowski P, Holick MF, Grant WB, Konstantynowicz J, Mascarenhas MR, Hag A, et al. Vitamin D supplementation guidelines. Journal of Steroid Biochemistry and Molecular Biology 2018; 175: 125-35. https://www.sciencedirect.com/science/article/pii/S0960076017300316
- Toward Optimized Practice. Guideline for Vitamin D Testing and Supplementation. May 2014. http://www.topalbertadoctors.org/cpgs/?sid=18&cpg_cats=91
- Veugelers PJ, Ekwaru JP. A statistical error in the estimation of the Recommended Dietary Allowance for vitamin D. Nutrients 2014, 6: 4472-5. http://www.mdpi.com/2072-6643/6/10/4472
- Heaney R, Garland C, Baggerly C, French C, Gorham E. Letter to Veugelers, PJ and Ekwaru, JP, A statistical error in the estimation of the Recommended Dietary Allowance for vitamin D. Nutrients 2015, 7: 1688-90. http://www.mdpi.com/2072-6643/7/3/1688
- Vieth R. Why the minimum desirable serum 25-hydroxyvitamin D level should be 75 nmol/L (30 ng/mL). Best Practice & Research Clinical Endocrinology & Metabolism 2011, 25: 681-91. http://www.bprcem.com/article/S1521-690X(11)00073-X/fulltext
- Ameri P, Bovio M, Murialdo G. Treatment for vitamin D deficiency: here and there do not mean everywhere. European Journal of Nutrition 2012, 51: 257-9. https://link.springer.com/article/10.1007%2Fs00394-012-0316-6
- Grant WB. Is the Institute of Medicine report on calcium and vitamin D good science? Biological Research for Nursing 2011, 13: 117-9. http://journals.sagepub.com/doi/abs/10.1177/1099800410396947
- Heaney RP, Holick MF. Why the IOM recommendations for vitamin D are deficient. Journal of Bone and Mineral Research 2011, 26: 455-7. http://onlinelibrary.wiley.com/doi/10.1002/jbmr.328/abstract
- Holick MF. Evidence-based D-bate on health benefits of vitamin D. Dermato-Endocrinology 2012, 4: 183-90. http://www.tandfonline.com/doi/abs/10.4161/derm.20015
- Srivastava T, Garg U, Ruiz M, Dai H, Alon US. Serum 25(OH)D-vitmain D level in children: is there a need to change the reference range based on 2011 Institute of Medicine report? Clinical Pediatrics 2011, 52: 178-82. http://journals.sagepub.com/doi/abs/10.1177/0009922811425954?journalCode=cpja
- National Academies of Science Engineering and Medicine. May 15, 2017 Memorandum. Purported mathematical errors in the 2011 IOM report, Dietary Reference Intakes: Calcium and Vitamin D. https://www.nap.edu/resource/13050/Vit%20D%20panel%20report%20final.pdf
- National Academies of Science Engineering and Medicine. May 15, 2017 Memorandum. Impact on the RDA for vitamin D of mathematical errors in the 2011 IOM report, Dietary Reference Intakes: Calcium and Vitamin D. https://www.nap.edu/resource/13050/FINAL%20Vitamin%20D%20Phase%20II%20Panel%20Report_11-17-17.pdf