According to new US research the recommended dietary allowances (RDAs) of vitamin D is based on a miscalculation and should actually be higher than the tolerable upper level for the nutrient.
In 2011 the US Institute of Medicine (IoM) 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. According to two new publications, this is not enough. The first publication states that the IoM’s 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 (1). Many Canadians will still be vitamin D deficient or insufficient, even if they follow Health Canada’s recommendation of 600 IU per day, the researchers commented.
In a second publication, scientists call for a re-evaluation of the vitamin D RDA to account for body weight (2). Although differences in serum vitamin D concentrations by body mass index (BMI) and by absolute body weight have been reported in several studies, the RDA does not consider either, they say. 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. 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. The dose required for overweight or obese individuals to reach optimal 25(OH)D levels is actually 12,000-20,000 IU/day, 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/day, even with normal weight. The researchers recommend clinical guidelines for vitamin D supplementation to be specific for normal weight, overweight and obese individuals.