Five years ago, it seemed like government advice had finally caught up with the evidence.
At the time, the Institute of Medicine (IOM) – a semi-official body that sets the U.S. recommended daily allowances for nutrients – raised the RDAs for vitamin D substantially.
The IOM raised the recommended daily allowance (RDA) for vitamin D from 400 IU to 600 IU, for people from one to 70 years of age.
While most researchers welcomed the increase, many vitamin D experts said it didn't go far enough, and called for RDAs of up to 1,700 IU.
However, according to two new papers, even an RDA of 1,700 IU would fall short of most people's actual need for vitamin D.
Vitamin D deficiency can trigger or worsen the risks for osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases, and cardiovascular diseases.
There's also some evidence that high levels of vitamin D reduce the risk of several types of cancer and type-1 and -2 diabetes.
Our bodies make vitamin D upon exposure of the skin to UV sunrays … but the winter sun in most northern regions is so weak that the body makes little or no vitamin D for months at a time.
Given that reality, and the fact that many Americans lead largely indoor lives, they (especially dark-skinned people) must rely on supplements or fatty seafood to get vitamin D.
So the accuracy of the RDA matter a great deal to public health.
Calculation of current RDA suffered from math errors
The IOM erred when it set the current RDA, say researchers from the University of Alberta.
The authors of the paper found that the IOM's 2010 RDA was based on a miscalculation, is much too low, and will harm public health (Veugelers PJ, Ekwaru JP 2014).
Back in 2010, the IOM analyzed 10 studies to calculate an RDA that would result in 97.5% of people reaching the widely agreed optimal minimum blood level of 50 nmol/L.
The IOM panel examined vitamin D supplementation studies conducted in northern latitudes during winter months, to minimize the influence of vitamin D generated by exposure to sunrays.
It matters a great deal if the IOM blew the math ... and they appear to have done just that.
The University of Alberta scientists found that an RDA of 600 IU actually means that 97.5% of people would achieve a blood level at or above 26.8 nmol/L, rather than 50 nmol/L or more.
They analyzed the same studies, and calculated that it would take an RDA of 8,895 IU in order for 97.5% of people to achieve blood levels of 50 nmol/L or more.
The authors made two key points (Veugelers PJ, Ekwaru JP 2014):
- "As this dose is far beyond the range of studied doses, caution is warranted when interpreting this estimate."
- "Regardless, the very high estimate illustrates that the [appropriate daily] dose is well in excess of the current RDA of 600 IU per day and the tolerable upper intake of 4000 IU per day."
Importantly, their conclusion was supported by renowned vitamin D experts from Creighton University and the University of California, who examined a different set of studies and calculated the need for a similarly high RDA.
As they wrote, "... we confirm the findings of these investigators with regard to the published RDA for vitamin and we call for the IOM and all public health authorities ... to designate, as the RDA, a value of approximately 7,000 IU per day ..." (Heaney R et al. 2015).
Vitamin RDA also depends on weight
The authors of a second paper call for a re-evaluation of the vitamin D RDA to account for body weight.
Because body fat sequesters this fat-soluble vitamin, it takes more supplemental vitamin D to raise blood levels in overweight and obese people.
The paper was authored by vitamin D experts from the University of Calgary, the Boston University School of Medicine, and the Harvard School of Public Health (Ekwaru JP et al. 2014).
As they wrote, "Although differences in vitamin D by body mass index (BMI) and by absolute body weight have been reported [in eight other papers], the RDA does not consider either [factor].”
Analysis of vitamin D intakes and levels in more than 20,000 people indicated that the current RDA of 600 IU is too low to achieve optimal vitamin D status.
Indeed, the dose needed for overweight or obese individuals to reach optimal vitamin D levels is 12,000-20,000 IU.
That's two to three times higher than the amount needed by a normal weight individual, and four to five times higher than the maximum intake currently recommended (4,000 IU per day).
With a significant portion of the US population being overweight or obese, the findings have potentially serious implications.
The new analysis also showed that vitamin D supplementation was safe up to 20,000 IU per day, even for normal weight people.
"We recommend clinical guidelines for vitamin D supplementation be specific for normal weight, overweight and obese individuals,” they concluded.
Double the IOM's recommended upper vitamin D intake limit deemed safe
When the IOM panel raised the RDA for vitamin D, it also doubled the "Tolerable Upper Intake Level”—the safe intake limit—for adults, from 2,000 IU to 4,000 IU per day.
Now, research from the Mayo Clinic supports the safety of a much higher tolerable upper limit of vitamin D intake (Dudenkov DV et al. 2015).
The Mayo study endorsed the limit espoused by the Endocrine Society, which is 10,000 IU of vitamin D daily … significantly higher than the recommendation from the Institute of Medicine.
Mayo Clinic researchers found that from 2002 to 2011 there was a 26-fold increase in the number of study participants with high vitamin D levels (i.e., above 50 ng/mL).
Despite the higher vitamin D levels, the incidence of vitamin D toxicity did not rise.
As the authors noted, that increase was most likely attributable to increased vitamin D supplementation, due to the public's rising awareness of vitamin D deficiency and the nutrient's benefits.
However, the Mayo Clinic researchers stopped short of endorsing the Endocrine Society's recommendations.
They note that even though the levels achieved by taking 10,000 IU of vitamin D daily are safe, they have not been proven helpful – especially for the general population.
They also echo the concerns IOM voiced when setting the current upper limit for vitamin D, because very high vitamin D levels are linked to slightly increased risks of death, heart disease, cancers and falls and fractures.
That said, the study should give health care practitioners greater confidence in recommending daily vitamin D intakes of up to 2,000 IU daily for healthy people and 3,000 to 4,000 IU for those deficient in the vitamin.
- 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 Clin Proc. 2015 May;90(5):577-86. doi: 10.1016/j.mayocp.2015.02.012.
- 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 Nov 5;9(11):e111265. doi: 10.1371/journal.pone.0111265. eCollection 2014
- Heaney R et al. Letter to Veugelers, P.J. and Ekwaru, J.P., A Statistical Error in the Estimation of the Recommended Dietary Allowance for Vitamin D.Nutrients. 2015 Mar; 7(3): 1688–1690.Published online 2015 Mar 10. doi: 10.3390/nu7031688
- Veugelers PJ, Ekwaru JP. A statistical error in the estimation of the recommended dietary allowance for vitamin D. Nutrients. 2014 Oct 20;6(10):4472-5. doi: 10.3390/nu6104472.