RESUMO
Frei et al's 2012 review entitled "Authors' Perspective: What is the Optimum Intake of Vitamin C in Humans" is both flawed and misleading. RCTs are ill suited to determining the RDA, it is debatable that there is sufficient scientific evidence to determine the optimum intake of vitamin C in humans, observations regarding high-doses of ascorbate have been ignored, and there are inaccuracies of fact with respect to the saturation of blood plasma following low dose intake. Until the limitations of current knowledge are recognised it is unwise to set limits on the dose.
RESUMO
A large and rapidly expanding body of scientific literature exists on the roles of vitamin D in maintaining optimal health and reducing the risk of chronic and infectious diseases. Serum 25-hydroxyvitamin D [25(OH)D] levels for optimal health are in the range of 100-150 nmol/L; mean population values in The Netherlands are around 50-63 nmol/L. Health problems for which there exists good observational evidence and some randomized controlled trial evidence that vitamin D reduces risk include many types of cancer, cardiovascular disease, diabetes mellitus, bacterial and viral infections, autoimmune diseases, osteoporosis, falls and fractures, dementia, congestive heart failure, and adverse pregnancy outcomes. Reductions in incidence and mortality rates for various diseases and all-cause mortality rates can be determined from ecological, observational and cross-sectional studies and randomized controlled trials. For The Netherlands, raising mean serum 25(OH)D levels to 105 nmol/L is estimated to reduce specific disease rates by 10-50% and all-cause mortality rates by 18%. To raise serum 25(OH)D levels by this amount, inhabitants in The Netherlands would have to increase vitamin D production or oral intake by 2500-4000 IU/day. Doing so would pose only minimal increased risks of melanoma or skin cancer or hypercalcemia.