Primary Research · 2015
Dietary fat increases vitamin D-3 absorption
Dawson-Hughes et al. · Journal of the Academy of Nutrition and Dietetics, 2015
Key finding
Monounsaturated-fat-rich meal increased vitamin D3 absorption by ~32% compared to low-fat meal.
Abstract
PubMed · PMID 25441954 →BACKGROUND: The plasma 25-hydroxyvitamin D response to supplementation with vitamin D varies widely, but vitamin D absorption differences based on diet composition is poorly understood. OBJECTIVES: We tested the hypotheses that absorption of vitamin D-3 is greater when the supplement is taken with a meal containing fat than with a fat-free meal and that absorption is greater when the fat in the meal has a higher monounsaturated-to-polyunsaturated fatty acid ratio (MUFA:PUFA). DESIGN: Open, three-group, single-dose vitamin D-3 comparative absorption experiment. PARTICIPANTS/SETTING: Our 1-day study was conducted in 50 healthy older men and women who were randomly assigned to one of three meal groups: fat-free meal, and a meal with 30% of calories as fat with a low (1:4) and one with a high (4:1) MUFA:PUFA. After a 12-hour fast, all subjects took a single 50,000 IU vitamin D-3 supplement with their test breakfast meal. MAIN OUTCOME MEASURES: Plasma vitamin D-3 was measured by liquid chromatography-mass spectrometry before and 10, 12 (the expected peak), and 14 hours after the dose. STATISTICAL ANALYSES PERFORMED: Means were compared with two-tailed t tests for independent samples. Group differences in vitamin D-3 absorption across the measurement time points were examined by analysis of variance with the repeated measures subcommand of the general linear models procedure. RESULTS: The mean peak (12-hour) plasma vitamin D-3 level after the dose was 32% (95% CI 11% to 52%) greater in subjects consuming fat-containing compared with fat-free meals (P=0.003). Absorption did not differ significantly at any time point in the high and low MUFA and PUFA groups. CONCLUSIONS: The presence of fat in a meal with which a vitamin D-3 supplement is taken significantly enhances absorption of the supplement, but the MUFA:PUFA of the fat in that meal does not influence its absorption.
Copyright © 2015 Academy of Nutrition and Dietetics. Published by Elsevier Inc. All rights reserved. Abstract sourced from PubMed, a database of the U.S. National Library of Medicine. Displayed in the authors’ own words for context; our critique is in the sections below.
Read the full paper
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How to read a study like this
The same questions worth asking about any research paper, not just this one. Worth a minute even if you trust the grade.
Who was studied, and do you resemble them?
Supplement effects often depend on baseline status. Vitamin D helps people who are deficient; iron helps people who are anemic. A result in people unlike you may not apply to you.
What was measured, and does it matter in daily life?
A study that shows a blood marker moved isn't the same as a study that shows people felt or functioned better. Ask what the outcome means in practice.
How large was the effect — not just whether it was significant.
'Statistically significant' only means the effect is unlikely to be zero. It doesn't tell you the effect is large enough to notice. Look for effect sizes, not just p-values.
Who paid for the trial, and what did they stand to gain?
Industry-funded trials are several times more likely to report positive results than independent ones. It's not usually fraud — it's subtle design and reporting choices. Weight accordingly.
Has anyone else replicated this?
Single positive trials are hypotheses. Replication by independent groups is what turns a hypothesis into reliable evidence. If the only positive trial is the one you're reading, wait.
Does the dose in the trial match what's being sold?
Supplement marketing routinely cites trials that used 5–10× the dose in the product. If the effective dose was 2 g/day and the capsule has 200 mg, expect roughly no effect.
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