Did the Institute of Medicine miscalculate the RDA for vitamin D?
In 2011 the Institute of Medicine announced an increase to the recommended dietary allowances (RDAs) of vitamin D from 400 IU to 600 IU per day for persons 1 to 70 years of age. While many people welcomed the increase, many vitamin D experts said it didn’t go far enough, and called for doses in excess of 1,700 IU.
However, according to two new papers, even this will not be enough.
The first paper, published in Nutrients and authored by Paul Veugelers and John Paul Ekwaru from the School of Public Health at University of Alberta, states that the Institute of Medicine’s 2011 RDA was based on a miscalculation, and the potential vitamin D deficiency that this could produce has the potential to be a serious Canadian public health issue with significant cost and health impacts.
“The public health and clinical implications of an error in the calculation of the recommended dietary allowance for Vitamin D are serious, particularly for residents of Canada,” said Dr Veugelers. “Current public health targets are not being met. Many Canadians will still be vitamin D deficient or insufficient, even if they follow Health Canada's recommendation of 600 IU per day.”
The sunshine vitamin
According to the 2014 CRN Consumer Survey on Dietary Supplements, vitamin D is the second leading category among supplement users after multivitamins.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 and -2 diabetes.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
IoM RDA
A second paper published in PLoS One, Veugelers and Ekwaru are joined by Jennifer Zwicker from the University of Calgary, Michael Holick from Boston University School of Medicine, and Edward Giovannucci from Harvard School of Public Health, and this paper calls for a re-evaluation of the vitamin D RDA to account for body weight.
“Although differences in serum 25(OH)D by body mass index (BMI) and by absolute body weight have been reported [in eight other papers], the RDA does not consider either,” they write.
Analysis of more than 20,000 measurements of 25(OH)D indicated that 600 IU/d is too low to achieve optimal vitamin D status.
Indeed, the dose required for overweight or obese individuals to reach optimal 25(OH)D levels is actually 12,000-20,000 IU/d; 2-3 times higher than the amount needed by a normal weight individual, and 4-5 times higher than the tolerable upper level of intake currently recommended. With a significant portion of both the US and Canadian 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/d, even with normal weight.
“We recommend clinical guidelines for vitamin D supplementation be specific for normal weight, overweight and obese individuals,” they concluded.
'Adding to the many uncertainties regarding vitamin D recommendations'
Commenting on the findings of the papers, Andrea Wong, PhD, VP of Scientific and Regulatory Affairs for Council for Responsible Nutrition (CRN), told us that the association continues to closely monitoring developments in the area of vitamin D research.
"The science continues to evolve; however, most people would benefit from vitamin D supplementation since food sources of this important nutrient are limited," she said.
"The report claiming a statistical error in estimating the RDA for vitamin D adds to the many uncertainties regarding vitamin D recommendations. Although serum 25(OH)D levels appear to be the appropriate marker of vitamin D status, variations in laboratory standards and analytical methods for 25(OH)D hinder the interpretation of test results, making it difficult to draw conclusions. Moreover, there is a lack of consensus on what cut-off level should be considered to demonstrate vitamin D insufficiency or deficiency, or even if using a cut-off is appropriate," said Dr Wong.
"With respect to the study on vitamin D and body weight, given that vitamin D requirements may differ depending on many factors such as age, sex, and genetics, it is not surprising that body weight and BMI can affect serum 25(OH)D levels following vitamin D supplementation. Overweight and obese individuals may need more supplemental vitamin D because the body fat sequesters this fat-soluble vitamin.”
Sources: Nutrients
Oct 2014, 6(10), pages 4472–4475, doi: 10.3390/nu6104472
“A Statistical Error in the Estimation of the Recommended Dietary Allowance for Vitamin D”
Authors: P.J. Veugelers, J.P. Ekwaru
PLoS One
Volume 9, Issue 11:e111265. doi: 10.1371/journal.pone.0111265
“The importance of Body Weight for the Dose Response Relationship of Oral Vitamin D Supplementation and Serum 25-Hydroxyvitamin D in Healthy”
Authors: J.P. Ekwaru, J.D. Zwicker, M.F. Holic, E. Giovannucci, P.J. Veugelers
