Prof. Heike A. Bischoff-Ferrari, Centre on Aging and Mobility, University of Zurich, Switzerland.
Prof. Walter C. Willett, Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, USA.
“Most evidence on vitamin D and calcium concerns bone health. Thus the recommendations by the Institute of Medicine (IOM) panel are largely based on bone health and call for 600 IU of vitamin D daily for all ages up to age 70 and 800 IU after the age of 71 (1). This assumes that most people get little sun exposure. The panel raised the safe upper limit of 2,000 IU daily to 4,000 IU for adults, and declared a safe upper limit of 1,000 to 3,000 IU per day for children, depending on their age. According to the IOM, a vitamin D serum concentration of 50 nmol/l is sufficient for 97% of the population, including bone health as the main endpoint.
While the IOM recommendation of an increase in vitamin D intake is supported by the available data from double-blind randomized controlled trials (RCTs) of fracture risk, a threshold of 50 nmol/l for its 25(OH)D blood level is not. In two 2009 meta-analyses of double-blind RCTs, a threshold of 50 nmol/l was insufficient for fracture or fall reduction based on achieved 25(OH)D levels in the treatment groups (2, 3). Furthermore, in the very large American population-based NHANES analysis, bone density increased with higher 25(OH)D levels far beyond 50 nmol/l in younger and older adults (4), suggesting that the IOM threshold recommendation is too low for optimal bone health in adults. In contrast to the IOM report, the International Osteoporosis Foundation (IOF) recommended in their 2010 position paper on vitamin D a threshold of 75 nmol/l for optimal fall and fracture reduction, and recommended 800 to 1,000 IU vitamin D per day for seniors aged 60 years and older (5).
With the IOM recommendation of 600 to 800 IU of vitamin D, most healthy adults will reach 50 nmol/l 25(OH)D, but not optimal bone health with respect to hip bone density or fracture reduction. Despite evidence from several double-blind RCTs and a meta-analysis summarizing these data (3), the IOM report concluded that there is inconsistent evidence on vitamin D and fall prevention. In contrast to the IOM report, the evidence of the effect of vitamin D supplementation at a dose of 700 to 1,000 IU of vitamin D per day on fall reduction was acknowledged by the 2010 IOF position paper on vitamin D (5).
Although the benefits of serum concentrations of 25(OH)D higher than 50 nmol/l on endpoints other than bone health have not been documented by randomized trials, the evidence for benefits is quite strong in some instances, especially colorectal cancer (6). The IOM conclusion that intakes of vitamin D are adequate for most of the US population assumes that a lack of randomized trials means a lack of benefit, which seems illogical. At a minimum, the conclusion should indicate uncertainty about the benefit of higher intakes and blood levels.
In support of a greater safety margin in research and supplementation strategies, the IOM doubled the safe upper limit from 2,000 IU to 4,000 IU of vitamin D per day, which is appropriate.”