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Should 1000 IU be the new RDA for vitamin D?

Since it was set in 2010, the 600 IU vitamin D RDA has been widely circulated. But a close look at individual patient data may give a more accurate estimate of vitamin D needs.

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Study under review: Improved Dietary Guidelines for Vitamin D: Application of Individual Participant Data (IPD)-Level Meta-Regression Analyses

Introduction

Vitamin D deficiency is generally accepted to be a blood level of 25-hydroxyvitamin D {25(OH)D} less than 20 nanograms per milliliter (ng/mL) or 50 nanomoles per liter (nmol/L), a threshold supported by both the National Academies of Sciences[1] and the Endocrine Society[2]. As with other vitamins and minerals, government bodies have established recommendations for the dietary intake of vitamin D to prevent deficiency in the general population.

One such recommendation, put forth by the National Academies of Sciences, is the recommended daily allowance (RDA) of 600 IU per day[1] for both children and adults up to age 70. The RDA represents a level of intake believed to meet the nutritional requirement of 97.5% of the population. As such, virtually all people should be able to increase their blood levels of 25(OH)D to above 20 ng/mL by consuming 600 IU of vitamin D per day, be it from food or supplements. Importantly, the studies used to establish the RDA were performed exclusively in Northern regions during winter months to rule out the possibility that skin exposure to sunlight contributed to vitamin D requirements (since we naturally make vitamin D when the skin is exposed to sunlight or UVB radiation).

The National Academies of Sciences used a standard meta-regression approach to analyze several large randomized controlled trials to determine their vitamin D recommendations. Essentially, vitamin D intake is plotted on the x-axis and 25(OH)D levels are plotted on the y-axis. Each data point represents one study, an average value representing all individuals. Although this approach accounts for between-study variability, it cannot incorporate between-participant variability, which is crucial for estimating individual recommendations.

If we instead plot every single participant used to determine the plotted averages in the standard meta-regression, then we have a meta-regression based on individual participant data (IPD). This approach is considered[3] the gold standard for aggregating data because it minimizes publication and reporting biases and allows for detailed data checking and verification. The study at hand was an IPD meta-regression of several large randomized controlled trials to determine the dose-response effect of vitamin D intake on serum 25(OH)D levels and compare this result with that obtained using a standard meta-regression of the same data.

Current recommendations for vitamin D intake were formulated with the use of a standard meta-regression analysis that looks at group averages rather than individuals. Using individual participant data is considered the gold standard when aggregating data because it incorporates between-people variability, minimizes publication and reporting biases, and allows for detailed data checking and verification. The study under review conducted a meta-regression of several randomized controlled trials to determine vitamin D requirements using both standard methods and individual participant data.
Table 1: Vitamin D recommendations around the world
ThresholdRecommendation
Scientific Advisory Committee on Nutrition (United Kingdom)10 ng/mL400 IU
Nordic Council of Ministers (Nordic countries)20 ng/mL400 IU
National Academies of Sciences (USA & Canada)20 ng/mL600 IU
European Food Safety Authority (European Union)20 ng/mL600 IU
The German Nutrition Society (Germany)20 ng/mL800 IU

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