Ultramarathons: Can vitamin D protect your bones?

Normal Curves: Sexy Science, Serious Statistics

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24d ago 58:50

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Ultramarathoners push their bodies to the limit, but can a giant pre-race dose of vitamin D really keep their bones from breaking down? In this episode, we dig into a trial that tested this claim – and found a statistical endurance event of its own: six highly interchangeable papers sliced from one small study. Expect missing runners, recycled figures, and a peer-review that reads like stand-up comedy, plus a quick lesson in using degrees of freedom as your statistical breadcrumbs.

Statistical topics

Data cleaning and validation
Degrees of freedom
Exploratory vs confirmatory analysis
False positives and Type I error
Intention-to-treat principle
Multiple testing
Open data and transparency
P-hacking
Salami slicing
Parametric vs non-parametric tests
Peer review quality
Randomized controlled trials
Research reproducibility
Statistical sleuthing

Methodological morals

“Degrees of freedom are the breadcrumbs in statistical sleuthing. They reveal the sample size even when the authors do not.”
“Publishing the same study again and again with only the outcomes swapped is Mad Libs Science, better known as salami slicing.”

References

Boswell, Rachel. Pre-race vitamin D could do wonders for ultrarunners’ bone health, according to science. Runner’s World. September 25, 2025.
Mieszkowski J, Stankiewicz B, Kochanowicz A, et al. Ultra-Marathon-Induced Increase in Serum Levels of Vitamin D Metabolites: A Double-Blind Randomized Controlled Trial. Nutrients. 2020;12(12):3629. Published 2020 Nov 25. doi:10.3390/nu12123629
Mieszkowski J, Borkowska A, Stankiewicz B, et al. Single High-Dose Vitamin D Supplementation as an Approach for Reducing Ultramarathon-Induced Inflammation: A Double-Blind Randomized Controlled Trial. Nutrients. 2021;13(4):1280. Published 2021 Apr 13. doi:10.3390/nu13041280
Mieszkowski J, Brzezińska P, Stankiewicz B, et al. Direct Effects of Vitamin D Supplementation on Ultramarathon-Induced Changes in Kynurenine Metabolism. Nutrients. 2022;14(21):4485. Published 2022 Oct 25. doi:10.3390/nu14214485
Mieszkowski J, Brzezińska P, Stankiewicz B, et al. Vitamin D Supplementation Influences Ultramarathon-Induced Changes in Serum Amino Acid Levels, Tryptophan/Branched-Chain Amino Acid Ratio, and Arginine/Asymmetric Dimethylarginine Ratio. Nutrients. 2023;15(16):3536. Published 2023 Aug 11. doi:10.3390/nu15163536
Stankiewicz B, Mieszkowski J, Kochanowicz A, et al. Effect of Single High-Dose Vitamin D3 Supplementation on Post-Ultra Mountain Running Heart Damage and Iron Metabolism Changes: A Double-Blind Randomized Controlled Trial. Nutrients. 2024;16(15):2479. Published 2024 Jul 31. doi:10.3390/nu16152479
Stankiewicz B, Kochanowicz A, et al. Single high-dose vitamin D supplementation impacts ultramarathon-induced changes in serum levels of bone turnover markers: a double-blind randomized controlled trial. J Int Soc Sports Nutr. 2025 Dec;22(1):2561661. doi: 10.1080/15502783.2025.2561661.

Kristin and Regina’s online courses:

Demystifying Data: A Modern Approach to Statistical Understanding

Clinical Trials: Design, Strategy, and Analysis

Medical Statistics Certificate Program

Writing in the Sciences

Epidemiology and Clinical Research Graduate Certificate Program

Programs that we teach in:

Epidemiology and Clinical Research Graduate Certificate Program

Find us on:

Kristin - LinkedIn & Twitter/X

Regina - LinkedIn & ReginaNuzzo.com

00:00 Intro & claim of the episode
00:44 Runner’s World headline: Vitamin D for ultramarathoners
02:03 Kristin’s connection to running and vitamin D skepticism
03:32 Ultramarathon world—Regina’s stories and Death Valley race
06:29 What ultramarathons do to your bones
08:02 Boy story: four stress fractures in one race
10:00 Study design—40 male runners in Poland
11:33 Missing flow diagram and violated intention-to-treat
13:02 The intervention: 150,000 IU megadose
15:09 Blinding details and missing randomization info
17:13 Measuring bone biomarkers—no primary outcome specified
19:12 The wrong clinicaltrials.gov registration
20:35 Discovery of six papers from one dataset (salami slicing)
23:02 Why salami slicing misleads readers
25:42 Inconsistent reporting across papers
29:11 Changing inclusion criteria and sloppy methods
31:06 Typos, Polish notes, and misnumbered references
32:39 Peer review comedy gold—“Please define vitamin D”
36:06 Reviewer laziness and p-hacking admission
39:13 Results: implausible bone growth mid-race
41:16 Degrees of freedom sleuthing reveals hidden sample sizes
47:07 Open data? Kristin emails the authors
48:42 Lessons from Kristin’s own ultramarathon dataset
51:22 Fishing expeditions and misuse of parametric tests
53:07 Strength of evidence: one smooch each
54:44 Methodologic morals—Mad Libs Science & degrees of freedom breadcrumbs
56:12 Anyone can spot red flags—trust your eyes
57:34 Outro: skip the vitamin D shot before your next run

20 episodes