Vitamin D – How much?
Please Understand this First!
Not only are the current "recommendations" in serious question by most vitamin D experts, many vitamin D scientists (many of them published in AJCN, etc.) are frustrated by the lack of action by government agencies to increase the recommendations because of the serious consequences of insufficient vitamin D intake.
The graph in Figure 1 illustrates the disparity between the outdated "recommendations" and what scientists believe they should be based on many studies. Please note that these are only possible values.
One detailed report described the current 200-600 IU recommendations as "woefully inadequate and ineffective" in maintaining the apparently needed calcifediol (blood indicator of vitamin D) levels to maintain proper health and also "potentially harmful" The report is concluded saying that a "clearly merited" reexamination of the current DRI values will likely result in the needing to increase the recommended intake level above 2000 IU per day for adults.5
The American Journal of Clinical Nutrition published a paper in January 2007 in which the authors call into question the current upper intake levels saying that the absence of vitamin D toxicity in various prior studies safely allow for an upper limit of 10,000 IU.1 Furthermore another study concluded with respect to calcium absorption "that the lower end of the current reference range is set too low."2
You should always consult a physician before starting or modifying a supplementation program, especially if you're pregnant or lactating.
What's taking so long to change the Recommended Levels?
It's not that updating DRI (RDA) values is trivial. Depending on the nutrient they're considering, the assigned committee(s) may have to review up to hundreds studies, taking into account both deficiency and toxicity, before making their recommendations. The estimated date of report release for the currently assigned comittee on vitamin D/calcium is May 2010. Details about the committee's schedule can be found here. Unfortunately many of us believe that they have not demonstrated an urgency commensurate to the large body of sobering data available.
Current RDAs/AIs...(12 years old)
Most people are familiar with Recommended Dietary Allowances or "RDA". For vitamin D there is no RDA, but there is an "Adequate Intake" value or "AI". The AI for vitamin D depends on your age and whether you’re pregnant or lactating. The National Institute of Health says the AI is "established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy. [highlights added]" NIH defines Tolerable Upper Intake Level (UL) as the "maximum daily intake unlikely to cause adverse health effects"
In other words, in 1997--12 years ago--these estimated values were the best values they could come up with based on the studies up to that point.
| Age (years) | Adequate Intake (AI) per day (IU) | Tolerable Upper Intake Levels (UL) (IU) |
|---|---|---|
| Pregnant | 200 | 2000 |
| Lactating | 200 | 2000 |
| Less than 1* | 200 | 1000 |
| 1 – 50 | 200 | 2000 |
| 50-70 | 400 | 2000 |
| 70+ | 600 | 2000 |
| Amounts for Pregnant or Lactating take precedence over amounts based on age. |
* There is a qualification for "dark-skinned infants and children who are fed only breast milk". See Rickets
Sunlight and Vitamin D
Interestingly the amount our skin can produce in a short amount of time far exceeds the recommended amounts. At a latitude such as Chicago’s, in the summer, 15 minutes of full sun exposure by a fair skinned person can result in the production of around 10,000 IU (a darker skinned person would produce around half of that under similar conditions). So our skin can produce 5 to 10 times the “tolerable upper limit” mentioned above...without toxicity.
How much Vitamin D is too much? What's Safe?
So you might ask, “Can I skip the sun exposure and just take 10,000 IU of vitamin D?” Not necessarily. It may be that the vitamin D you ingest is more toxic than that produced by your skin (if the skin-produced type could ever reach toxicity because your body stops producing it around 10,000 IU or so). Nevertheless, a 2007 study published in the American Journal of Clinical Nutrition suggests that the current upper limit could safely be much higher than it currently is.1 Quoting yet another study: "The data support the feasibility of pharmacologic doses of vitamin D3 for clinical research, and they provide objective evidence that vitamin D intake beyond the current upper limit is safe by a large margin." 3
The following is quoted from a May 1999 publication of the American Journal of Clinical Nutrition (highlights added):
For adults, the 5-µg (200 IU) vitamin D recommended dietary allowance may prevent osteomalacia in the absence of sunlight, but more is needed to help prevent osteoporosis and secondary hyperparathyroidism. Other benefits of vitamin D supplementation are implicated epidemiologically: prevention of some cancers, osteoarthritis progression, multiple sclerosis, and hypertension. Total-body sun exposure easily provides the equivalent of 250 µg (10000 IU) vitamin D/d, suggesting that this is a physiologic limit....To ensure that serum 25(OH)D concentrations exceed 100 nmol/L, a total vitamin D supply of 100 µg (4000 IU)/d is required. Except in those with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25(OH)D concentrations <140 nmol/L, which require a total vitamin D supply of 250 µg (10000 IU)/d to attain. Published cases of vitamin D toxicity with hypercalcemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intake of >=1000 µg (40000 IU)/d. Because vitamin D is potentially toxic, intake of >25 µg (1000 IU)/d has been avoided even though the weight of evidence shows that the currently accepted...limit of 50 µg (2000 IU)/d is too low by at least 5-fold.4
An interesting "commentary" by the health products community on the current 400/600 IU (adult/elderly) Adequate Intake levels is the common availability of vitamin D in the 1000-2000 IU per capsule range.
Again, however, you should always consult a physician before starting or modifying a supplementation program, especially if you're pregnant or lactating.
See Also
Vitamin DVitamin D - Deficiency
Vitamin D - Excess/Toxicity
Vitamin D - Foods
References
1. Hathcock JN, Shao A, Vieth R, Heaney R. Risk assessment for vitamin D. Am J Clin Nutr, Vol. 85, No. 1, 6-18, January 2007
2. Heaney RP, Dowell MS, Hale CA, Bendich A. Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D. J Am Coll Nutr. 2003 Apr;22(2):142-6.
3. Kimball SM, Ursell MR, O'Connor P, Vieth R. Safety of vitamin D3 in adults with multiple sclerosis. Am J Clin Nutr. 2007 Sep;86(3):645-51.
4. Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr, Vol. 69, No. 5, 842-856, May 1999
5. Hollis, BW. Circulating 25-Hydroxyvitamin D Levels Indicative of Vitamin D Sufficiency: Implications for Establishing a New Effective Dietary Intake Recommendation for Vitamin D. In "Symposium: Vitamin D Insufficiency: A Significant Risk Factor in Chronic Diseases and Potential Disease-Specific Biomarkers of Vitamin D Sufficiency" © 2005 American Society for Nutritional Sciences.
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