A few weeks ago, the Institute of Medicine (IOM) surprised many of us when it announced its new dietary reference intake (DRI) for vitamin D. The consensus of the scientific community was that the previous DRI of 400 IU was insufficient, and that supplementation with at least 1,000 IU would be necessary for most people to achieve vitamin D sufficiency. The IOM disagreed.
The IOM's new recommendations call for 600 IU per day for children and adults under age 70 (formerly 400 IU; for adults over age 70, the new recommendation is 800 IU), and the tolerable upper limit (amount not to be exceeded in one day) has been raised to 4,000 IU from 2,000 IU. Their definition of vitamin D sufficiency is a 25(OH)D level of 20 ng/ml.
There has been a great deal of research in recent years on vitamin D's role in a variety of human diseases. Low vitamin D status has been associated with cardiovascular disease, certain cancers, cognitive decline, depression, diabetes, pregnancy complications, autoimmune diseases and even a 78 percent increase in all-cause mortality risk (<17.8 ng/ml 25(OH)D compared to >32.1 ng/ml). However, because there are not yet enough randomized controlled trials to clearly and conclusively confirm the benefits of vitamin D supplementation for conditions unrelated to bone health , the IOM did not find the existing evidence for non-skeletal conditions sufficient enough to raise the daily recommendations any higher than 600 IU. The 600 IU figure is based solely on bone health -- they did not take into account whether a greater quantity of vitamin D might be necessary to prevent non-skeletal diseases, even though there are vitamin D receptors in almost every cell of the human body.
Many experts are weighing in on -- and disagreeing with -- the IOM's report, and there is general agreement among the experts on these points:
I agree with those who have brought up these issues, including Dr. John Cannell of the Vitamin D Council, respected public health researcher Dr. Walter Willett and prominent vitamin D scientist Dr. Heike Bischoff-Ferrari. Cannell also stressed the importance of vitamin D during fetal development, advising pregnant women especially to confirm sufficient 25(OH)D levels. Walter Willett of the Harvard School of Public Health, together with Heike Bischoff-Ferrari published an online commentary stating that there is ample evidence that 20 ng/ml (the IOM's definition of sufficiency) is not even sufficient for bone health, according to recent meta-analyses.  A new meta-analysis of randomized controlled trials by Bischoff-Ferrari found that supplementation with a mean of approximately 1,400 IU (range 792-2,000 IU) allowed adults age 65 and older to achieve a significant reduction in fracture rate. Taking this into account, increasing from 600 to 800 IU as recommended by the IOM at age 70 may still be sub-optimal. [4, 5]
My recommendations have not changed as a result of the IOM's updated recommendations. I agree with the experts mentioned above that we cannot discount the epidemiologically suggested benefits of supplementation with more than 600 IU vitamin D because of a lack of randomized controlled trials existing at this time. Especially since the risk of toxicity is so low: the minimum dose known to produce toxicity when taken for an extended period of time is 10,000 IU/day or even 50,000 IU according to some reports, resulting in blood 25(OH)D of 140 ng/ml or greater.  According to the Vitamin D council, a single 30 minute dose of sunshine has the potential to stimulate the production of up to 10,000 IU vitamin D, so it is extremely unlikely that doses below 10,000 IU will cause harm. 
Comparison of my recommendations to those of the IOM and the Vitamin D Council:
Recommendations for 25(OH)D and Vitamin D supplementation (for adults)
Institute of Medicine: >20 ng/ml; 600 IU
Dr. Fuhrman: 35-55 ng/ml; 2000 IU*
Vitamin D Council: 50-80 ng/ml; 5000 IU*
*also recommends to adjust supplementation according to 25(OH)D level
A chart showing IOM's revised recommendations for Calcium and Vitamin D intake: from the IOM website
As you can see, the IOM is on the low extreme, the Vitamin D council on the high extreme, and my recommendations are more moderate.
What I recommend is a safe, conservative amount of vitamin D which is supported by the literature. Recent reviews by prominent vitamin D researchers taking into account several studies on hypertension and colorectal cancer (for which evidence for a beneficial effect of vitamin D is quite strong) in addition to bone health concluded that 30 ng/ml should be the minimum sufficient level, and that a desirable range was approximately 36-48 ng/ml. I agree with this.
About 50 percent of North Americans have blood levels lower than 30 ng/ml. They further estimated that supplementation of at least 1000 IU would be necessary for most people to reach this desirable range. [8-10] The IOM's recommendation falls short of these figures. The IOM claims to be conservative, citing potential risks of over-supplementation, but I believe it is safer and more conservative to take the studies on non-skeletal conditions into account. The IOM with their still low recommended level of D may be taking risks with our lives here; my guidelines and D recommendations are more conservative and sensible given the strong possibility that 25(OH)D levels in the 20s may not be ideally protective, and certainly blood levels in the 30s and 40s could not be dangerous, since exposure to sunshine brings levels even higher than that.
It has been my experience that most people can reach sufficiency (defined by 35 ng/ml) with a 1,500-3,000 IU dose of vitamin D. We want to assure optimal levels, not just prevent deficiencies, and supplementing with 1,500-3,000 IU still falls well below the new tolerable upper limit of 4,000 IU.
The Vitamin D Council bases their higher recommendations on a body of research demonstrating the importance of vitamin D for fetal development, and vitamin D deficiency of millions of pregnant women (and their infants). They have concluded that 5,000 IU is an appropriate dose for pregnant women, and recommend that as a starting dose for all adults. Their recommended 25(OH)D level is at least 50 ng/ml for healthy people and higher for people with chronic diseases. As mentioned above, reviews of the literature have found that 36-48 ng/ml is likely the optimal range for disease prevention. [8, 9] The study on vitamin D levels and mortality agrees with this conclusion: 25(OH)D of 30-49 ng/ml was associated with the lowest mortality risk, and there was a significant (though slight) increase in risk above 50 ng/ml in women. 
Skin color, geographical location, time spent outside, sunscreen use, age etc., are all factors in how much vitamin D is produced by the skin (and therefore how much vitamin D is present and active in the body) before we take any supplements. People can differ greatly in the amount of Vitamin D required. So the supplemented dose is best determined by blood test, not by a predetermined amount set by the IOM or anyone else. Even then, the supplements we take may have varying potencies - some studies have found D2 to be less active, while others disagree. In my practice, and vast experience monitoring Vitamin D levels over the last ten years or more, I have noticed that those taking D2 need a greater number of IUs compared to D3 to reach similar 25(OH)D levels.
A note on Calcium recommendations. Along with these new vitamin D recommendations by the IOM came revisions of their calcium recommendations, as shown in the chart above. Much of the scientific community has also been in agreement that calcium recommendations for Americans have been too high. For example, the World Health Organization advises an intake of 500 mg, whereas the IOM recommends 1000 mg. When making calcium recommendations, the interplay with vitamin D is important. As was found in the meta-analysis by Bischoff-Ferrari and Willett, vitamin D supplements in the range of 792-2000 IU were required to protect against osteoporosis-related fracture, demonstrating the inadequacy of the IOM's recent pronouncement. However, the most interesting finding here was related to calcium: low dose calcium supplementation (500 mg) combined with vitamin D supplementation reduced osteoporosis fracture rates, but high dose calcium supplements (1000 mg or more) combined with vitamin D supplementation did not. [3-5] These results suggest that high dose calcium blunts the beneficial effects of vitamin D. Furthermore, a recent meta-analysis has revealed that there is potential for cardiovascular harm from taking high dose calcium supplements.  I advise caution here - conventional (high) levels of calcium supplementation (above 1000 mg) are not only unnecessary, but may even be counter-productive.
Guidelines for safe and effective supplementation with vitamin D:
1. Melamed, M.L., et al., 25-Hydroxyvitamin D Levels and the Risk of Mortality in the General Population. Archives of Internal Medicine, 2008. 168(15): p. 1629-1637.
2. Zhang, R. and D.P. Naughton, Vitamin D in health and disease: Current perspectives. Nutr J, 2010. 9(65).
3. Bischoff-Ferrari, H.A. and W. Willett Comment on the IOM Vitamin D and Calcium Recommendations. Harvard School of Public Health: The Nutrition Source, 2010.
4. Zoler, M.L., High Vitamin D Intake Linked to Reduced Fractures. Family Practice News, 2010(November 16, 2010).
5. Bischoff-Ferrari, H.A., Orav, E.J., Willett, W. et al., A Higher Dose of Vitamin D is Required for Hip and Non-vertebral Fracture Prevention: A Pooled Participant-based Meta-analysis of 11 Double-blind RCTs, in The American Society for Bone and Mineral Research 2010 Annual Meeting2010: Toronto, Ontario, Canada.
6. Vieth, R., Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr, 1999. 69(5): p. 842-56.
7. Cannel, J.J. Vitamin D Council Statement on FNB Vitamin D Report. 2010.
8. Bischoff-Ferrari, H.A., Optimal serum 25-hydroxyvitamin D levels for multiple health outcomes. Adv Exp Med Biol, 2008. 624: p. 55-71.
9. Bischoff-Ferrari, H.A., et al., Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr, 2006. 84(1): p. 18-28.
10. University of California - Riverside (2010, July 19). More than half the world's population gets insufficient vitamin D, says biochemist. ScienceDaily July 28, 2010]; Available from: http://www.sciencedaily.com/releases/2010/07/100715172042.htm.
11. Holick, M.F., et al., Vitamin D2 Is as Effective as Vitamin D3 in Maintaining Circulating Concentrations of 25-Hydroxyvitamin D. Journal of Clinical Endocrinology & Metabolism, 2007. 93(3): p. 677-681.
12. Bolland, M.J., et al., Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. Bmj, 2010. 341: p. c3691.
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