Normal Curves: Sexy Science, Serious Statistics

Bonus: Vitamin D Part 1 with commentary

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Dec 29, 2025

Dive into the vitamin D conundrum as the hosts unravel the claims of a deficiency epidemic. Discover the surprising surfer study from Hawaii that challenges assumptions about sun exposure and vitamin D levels. Explore the clash between differing medical guidelines and how arbitrary thresholds can warp our understanding of health. With a touch of statistical sleuthing, they highlight biases, conflicts of interest, and the nuances behind dietary recommendations. Get ready for a captivating discussion that questions the very data behind vitamin D health claims.

01:29:19

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ADVICE

Don’t Confuse RDA With Deficiency

Understand that RDA is average need plus two standard deviations, not a deficiency cutoff.
Do not treat the 20 ng/mL RDA as a universal diagnostic threshold without clinical context.

insights

INSIGHT

Why Guidelines Diverged

Guideline panels differed: IOM was conservative (glass half empty); Endocrine Society was permissive (glass half full).
Differences arose from selective evidence use and committee approaches.

question_answer

ANECDOTE

Holick’s Role As Vitamin D Evangelist

Michael Holick, a prominent vitamin D advocate, moved from bench work to public health and popular books advocating sun and supplements.
His activism and industry ties fueled controversy and public interest.

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Why question the vitamin D epidemic claim

06:25 • 3min

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Where vitamin D comes from and why it matters

09:09 • 4min

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Rickets, osteomalacia, and bone problems explained

13:32 • 3min

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Surfer study that sparked headlines

16:12 • 3min

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Questioning the study: definitions matter

IOM versus Endocrine Society disagreement

29:49 • 3min

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Statistical detour: normal distributions and RDAs

33:18 • 6min

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Interpreting the RDA and population needs

39:41 • 3min

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Different guideline philosophies compared

Who is Michael Holick and his influence

52:18 • 7min

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Fact-checking Holick: exaggerated prevalence claims

59:36 • 8min

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Math errors and disappearing data in studies

01:07:11 • 8min

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Misleading citations and unrepresentative samples

01:14:48 • 2min

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Holick's controversies: conflicts and court testimony

01:16:50 • 4min

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Resolution: Endocrine Society reverses course

• Mentioned in 26 episodes

The Advantage

Why Organizational Health Trumps Everything Else in Business

Patrick Lencioni

In 'The Advantage', Patrick Lencioni makes a compelling case that the key to a company's success lies in its organizational health rather than its intelligence or technological prowess. He argues that healthy organizations, characterized by a cohesive leadership team, clear strategy, effective communication, and a unified culture, outperform their counterparts. Lencioni identifies three biases (the Sophistication Bias, the Adrenaline Bias, and the Quantification Bias) that prevent leaders from focusing on organizational health. The book provides a practical model for achieving organizational health, including four disciplines: building a cohesive leadership team, creating clarity, overcommunicating clarity, and reinforcing clarity through systems and practices. Lencioni draws on his extensive experience consulting with leading organizations to offer stories, tips, and anecdotes that illustrate the importance of organizational health in today's fast-changing business environment.

#20726

• Mentioned in 3 episodes

The vitamin D solution

M. F. Holick

The Vitamin D Solution" likely offers a comprehensive guide to understanding vitamin D, its importance for health, and how to ensure adequate levels. It may cover topics such as the role of vitamin D in bone health, immune function, and chronic disease prevention. The book likely provides practical advice on how to increase vitamin D intake through diet, supplements, and sun exposure. It may also address common misconceptions about vitamin D and provide evidence-based recommendations for optimal vitamin D levels. Readers might find guidance on topics such as choosing the right vitamin D supplement, understanding blood tests, and addressing vitamin D deficiency.

While we’re on a short break between seasons, we’re revisiting some of our favorite episodes from Season 1. This week, we’re re-releasing our deep dive into vitamin D and the origins of the so-called deficiency epidemic, with added commentary.

Is America really facing an epidemic of vitamin D deficiency? While this claim is widely believed, the story behind it is packed with twists, turns, and some pesky statistical cockroaches. In this episode, we’ll dive into a study on Hawaiian surfers, expose how shifting goalposts can create an epidemic, tackle dueling medical guidelines, and flex our statistical sleuthing skills. By the end, you might wonder if the real deficiency lies in the data.

Statistical topics

conflicts of interest
cut points and thresholds
dichotomization
incentives in science
measurement and classification
normal distribution
researcher biases
standard deviation
statistical sleuthing

Methodologic morals

“Arbitrary thresholds make for arbitrary diseases.”
“Statistical errors are like cockroaches: Where there’s one, there’s many.”

Note that all blood vitamin D levels discussed in the podcast are 25-hydroxyvitamin D levels given in units of ng/ml. To convert from ng/ml to nmol/L, use the formula: nmol/L=2.5*ng/ml. For example, a vitamin D level of 30 ng/mL corresponds to 75 nmol/L.

Citations
Dr. Rhonda Patrick: Micronutrients for Health & Longevity. Huberman Lab Podcast. May 1, 2022

Noh CK, Lee MJ, Kim BK, et al. A Case of Nutritional Osteomalacia in Young Adult Male. J Bone Metab. 2013; 20:51-55.

Binkley N, Novotny R, Krueger D, et al. Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab. 2007;92:2130-5.

Malabanan A, Veronikis IE, Holick MF. Redefining Vitamin D Insufficiency. Lancet. 1998;351:805-6.

Dawson-Hughes B, Heaney RP, Holick MF, et al. Estimates of optimal vitamin D status. Osteoporos Int. 2005;16:713-6.

Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357:266-81.

Cui A, Xiao P, Ma Y, et al. Prevalence, trend, and predictor analyses of vitamin D deficiency in the US population, 2001-2018. Front Nutr. 2022;9:965376.

Ross AC, Manson JE, Abrams SA, et al. The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know. J Clin Endocrinol Metab. 2011;96:53-8.

Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96:1911-30.

Manson JE, Brannon PM, Rosen CJ, et al. Vitamin D deficiency-is there really a pandemic. N Engl J Med. 2016;375:1817-20.

Conti G, Chirico V, Lacquaniti A, et al. Vitamin D intoxication in two brothers: be careful with dietary supplements. J Pediatr Endocrinol Metab. 2014;27:763-7.

Holick, Michael, et al. The UV Advantage. Ibooks, 2004.

Holick, Michael F. The Vitamin D Solution: A 3-Step Strategy to Cure Our Most Common Health Problems. Penguin Publishing Group, 2011.

Szabo, Liz. Vitamin D, the Sunshine Supplement, Has Shadowy Money Behind It. The New York Times. August 18, 2018.

Lee JM, Smith JR, Philipp BL, Chen TC, Mathieu J, Holick MF. Vitamin D deficiency in a healthy group of mothers and newborn infants. Clin Pediatr. 2007;46:42-4.

Holick MF. Vitamin D deficiency: what a pain it is. Mayo Clin Proc. 2003;78:1457-9.

Passeri G, Pini G, Troiano L, et al. Low Vitamin D Status, High Bone Turnover, and Bone Fractures in Centenarians. J Clin Endocrinol Metab. 2003;88:5109-15.

Armstrong, David. The Child Abuse Contrarian. ProPublica. September 16, 2018.

Irwig MS, Kyinn M, Shefa MC. Financial Conflicts of Interest Among Authors of Endocrine Society Clinical Practice Guidelines. J Clin Endocrinol Metab. 2018;103:4333-38.

Demay MB, Pittas AG, Bikle DD, et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024;109:1907-47.

McCartney CR, McDonnell ME, Corrigan MD, et al. Vitamin D Insufficiency and Epistemic Humility: An Endocrine Society Guideline Communication. J Clin Endocrinol Metab. 2024; 109:1948–54.

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