The number in this claim is not invented. It exists, but only under one specific and contested definition of "sufficient."

The largest global pooled analysis found that out of 67,340 records searched, 308 studies with 7,947,359 participants from 81 countries were eligible, and globally 15.7% (95% CrI 13.7-17.8), 47.9% (95% CrI 44.9-50.9), and 76.6% (95% CrI 74.0-79.1) of participants had serum 25-hydroxyvitamin D levels less than 30, 50, and 75 nmol/l respectively . The 76.6% figure, which rounds to "almost 80%," refers to everyone below 75 nmol/L (30 ng/mL).

That threshold is the crux. The US Institute of Medicine agreed that serum 25(OH)D below 30 nmol/L (12 ng/mL) is considered vitamin D deficiency, 30 to 50 nmol/L (12 to 20 ng/mL) is insufficiency, and 50 nmol/L (20 ng/mL) or above is sufficient . Under those official US thresholds, the picture is dramatically different. Using national survey data, the percentage of Americans aged 1 year and over at risk of vitamin D deficiency was 5.0% and at risk of inadequacy was 18.3% in 2011-2014 . That totals roughly 23%, not 80%.

Using an intermediate framing, a 2001-2018 NHANES analysis reported that the weighted prevalence of severe and moderate deficiency was 2.6% and 22.0%, and the prevalence of insufficiency and sufficiency was 40.9% and 34.5% , which places about 65% of Americans below 75 nmol/L. A separate NHANES analysis found national prevalences of deficiency and insufficiency of 28.9% and 41.4% respectively , or about 70% combined.

So the "true" answer ranges from roughly 23% to roughly 77% depending entirely on where you draw the line, and the claim quotes the highest possible figure without saying so.

Critically, the professional body that originally popularized the 30 ng/mL threshold has since moved away from it. The 2024 Endocrine Society guideline states: the panel suggests against routine screening for a 25(OH)D level to guide decision-making and against routine follow-up testing to guide vitamin D dosing, for generally healthy adults who do not otherwise have established indications for testing . The same guideline suggests against empiric vitamin D supplementation above the current DRI to lower disease risk in healthy adults younger than 75, and found no clinical trial evidence supporting routine screening for 25(OH)D in the general population . The Society's own announcement is explicit: "we do not recommend routine testing for vitamin D levels in any of these groups."

Advisers to the body that set the RDA have argued the deficiency problem is systematically overstated. To ensure everyone gets enough, the RDA was set at the high end of the population's needs, 600 to 800 units depending on age, so by definition nearly everyone's true requirement is below that .

METHODOLOGY AND CONTEXT

The global 76.6% figure: Pooled Bayesian meta-analysis of 308 population-based studies, 81 countries, 2000-2022. Meta-analyses were stratified by latitude, season, six WHO regions, World Bank income groups, gender, and age groups, and the study was registered with PROSPERO . It is a global figure heavily weighted by regions with high deficiency burden. It is not a US or Western figure, and the creator's audience context is San Diego, California.

Threshold definitions in play: - Deficiency: <12 ng/mL (IOM) vs <20 ng/mL (older Endocrine Society) - Insufficiency: 12-20 ng/mL (IOM) vs 20-30 ng/mL (older Endocrine Society) - "Almost 80%" requires the 30 ng/mL ceiling

The word "clinically": No clinical guideline currently treats sub-30 ng/mL as a clinical diagnosis requiring treatment in asymptomatic adults. The 2024 Endocrine Society guideline explicitly declines to define a screening threshold at all.