💊 Clinical Bottom Line

This letter presents an independent analysis of an observational cohort to support the claim that the Institute of Medicine’s (IOM) Recommended Dietary Allowance (RDA) for vitamin D is underestimated by an order of magnitude. The authors’ analysis suggests a total daily intake of approximately 7,000 IU is required to ensure 97.5% of the population achieves the IOM’s own target serum level of 20 ng/mL, a figure dramatically higher than the IOM’s current recommendation.

Results in Context

Main Results

The analysis of 3,657 individuals from the Grassroots Health cohort found that a supplemental vitamin D intake of 3,875 IU/day was required to ensure 97.5% of the population achieved a serum 25(OH)D level of at least 20 ng/mL (the IOM’s target).

• To reach the Endocrine Society’s target (30 ng/mL), a supplemental intake of 6,201 IU/day was needed.

• To reach the Grassroots Health target (40 ng/mL), a supplemental intake of 9,122 IU/day was needed.

Definitions and Total Intake

The authors argue that a true RDA must account for intake from all sources. Their data’s regression analysis showed a baseline 25(OH)D level (at zero supplemental intake) of 34 ng/mL, which they estimate corresponds to a basal intake from food and sun of over 3,000 IU/day. Therefore, the total intake required to meet the IOM’s 20 ng/mL target is the sum of the supplemental (3,875 IU) and basal (3,000 IU) amounts, which the authors state is “close to 7000 IU per day”.

Participants

The analysis included 3,657 individuals from the GrassrootsHealth (GRH) database, with vitamin D intakes spanning from zero to above 10,000 IU/day.

Assertive Critical Appraisal

Limitations & Bias (STROBE Framework)

This document is a Letter to the Editor, not a full, peer-reviewed original research article. As such, methodological details are sparse. The analysis relies on an existing observational database (GrassrootsHealth). The primary limitation is the observational, non-randomized nature of the data. Furthermore, the method for ascertaining “intake” (e.g., self-report vs. diary) is not detailed in this letter, which could be a major source of measurement error and bias.

Reporting Quality Assessment (STROBE)

As a Letter, this document does not adhere to STROBE reporting guidelines. It is a brief communication focused on a single calculation. It is critical to note that the authors do not describe their efforts to address potential sources of confounding (e.g., age, BMI, season, latitude, baseline vitamin D status), which is a major methodological weakness in any observational analysis of vitamin D.

Reporting Quality Assessment (RECORD)

This study uses routinely collected health data from the GRH database. However, the letter fails to adequately describe the data source, how participants were selected from the database, and how key variables (intake, 25(OH)D levels) were defined and ascertained. These omissions are critical flaws that impede a full assessment of the study’s validity.

Applicability

The findings are provocative and highly relevant to general practice, as they directly challenge the adequacy of the official IOM recommendations for vitamin D. However, the conclusion—that an RDA of 7,000 IU/day is needed—is based on a brief observational analysis presented in a Letter. While the authors note this intake level is within established safety limits, this recommendation should be interpreted with caution until it is validated by regulatory bodies or through more rigorous, fully published studies.

Research Objective

To use an independent cohort (GrassrootsHealth) to validate the recent finding by Veugelers and Ekwaru that the IOM’s RDA for vitamin D was erroneously underestimated.

Study Design

This is a cross-sectional, observational analysis of data from the GrassrootsHealth database. The authors plotted serum 25(OH)D values against vitamin D supplement intake for 3,657 individuals to determine the intake required to ensure 97.5% of the cohort would achieve specific serum levels.

Setting and Participants

The data is from 3,657 individuals enrolled in the GrassrootsHealth (GRH) database. The letter does not specify participant eligibility criteria, locations, or dates of data collection.

Bibliographic Data

• Title: Letter to Veugelers, P.J. and Ekwaru, J.P., A Statistical Error in the Estimation of the Recommended Dietary Allowance for Vitamin D. Nutrients 2014, 6, 4472–4475; doi:10.3390/nu6104472

• Authors: Robert Heaney, Cedric Garland, Carole Baggerly, Christine French, and Edward Gorham

• Journal: Nutrients

• Year: 2015

• DOI: 10.3390/nu7031688

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