{
  "slug": "vitamin-d-deficiency-no-supplement",
  "question": "What are the odds of vitamin D deficiency if you don't take supplements?",
  "category": "food",
  "no_reliable_estimate": false,
  "perceived": {
    "description": "Most people who have heard of vitamin D deficiency associate it with rickets in Dickensian orphans, not with themselves. The modern indoor adult may vaguely know that sunlight is involved and assume that the occasional walk to the car park constitutes adequate UV exposure. Supplement marketing has raised awareness somewhat, but the default intuition is that deficiency is a niche problem for the housebound elderly or the extremely northern -- not something affecting a quarter to a third of ordinary US adults.\n",
    "rough_estimate": "~10-15% chance of being deficient without supplements",
    "kind": "intuition"
  },
  "native": {
    "display": "~24% prevalence of serum 25(OH)D <20 ng/mL among US adults (NHANES 2001-2018)",
    "numerator": 24,
    "denominator": 100,
    "unit": "cross-sectional prevalence of serum 25(OH)D <50 nmol/L (<20 ng/mL) among US adults",
    "population": "US adults aged 20+ in the NHANES survey (2001-2018 pooled)"
  },
  "normalized": {
    "lifetime_us_adult": 0.35,
    "display": "~35% lifetime probability that a non-supplementing US adult will be vitamin D deficient at some point",
    "log_value": -0.46,
    "assumptions": "NHANES 2001-2018 pooled data (n = 71,685) found 2.6% severe deficiency (<12 ng/mL) and 22% moderate deficiency (12-19 ng/mL) at any given cross-section, totalling ~24.6% point prevalence of serum 25(OH)D <20 ng/mL. Among non-supplement users, prevalence is higher -- Forrest & Stuhldreher (2011) found 41.6% deficiency (<20 ng/mL) in overall NHANES 2005-2006 data, with non-Hispanic blacks at 82.1%. However, that older analysis used less-refined assay standardisation. The CDC 2011-2014 report found ~23% at risk of deficiency or inadequacy combined. For lifetime probability: vitamin D status fluctuates seasonally and with age. A non-supplementing adult who experiences winters, ages past 65, or gains weight will dip below 20 ng/mL at some point with higher probability than the cross-sectional snapshot. Applying a modest cumulative adjustment (~1.4x the ~24% cross-sectional rate) yields ~35%, reflecting that seasonal troughs, illness, pregnancy, and ageing create repeated deficiency episodes over a 59-year adult horizon. This is conservative; some analyses suggest >40% of non-supplementing adults are deficient at any given moment.\n",
    "uncertainty": {
      "low": 0.22,
      "high": 0.5
    },
    "scope": "us_adult_lifetime"
  },
  "sources": [
    {
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC9573946/",
      "title": "Prevalence, trend, and predictor analyses of vitamin D deficiency in the US population, 2001-2018",
      "publisher": "Frontiers in Nutrition (Liu et al.)",
      "source_type": "peer_reviewed",
      "statistic": "Weighted prevalence of severe and moderate vitamin D deficiency: 2.6% and 22.0% respectively; insufficiency 40.9%",
      "excerpt": "\"Among 71,685 eligible participants, the weighted prevalence of severe and moderate vitamin D deficiency was 2.6% and 22.0%, respectively, with vitamin D insufficiency at 40.9% and sufficiency at 34.5%.\"\n",
      "source_date": "2022-10-07",
      "source_accessed": "2026-04-26",
      "archive_url": "http://web.archive.org/web/20260419141132/https://pmc.ncbi.nlm.nih.gov/articles/PMC9573946/",
      "calculation_notes": "NHANES 2001-2018 pooled analysis. Deficiency defined as serum 25(OH)D <12 ng/mL (severe) or 12-19 ng/mL (moderate), following the IOM cutoff of <20 ng/mL for combined deficiency. Total deficiency prevalence ~24.6%. Insufficiency (20-29 ng/mL) adds another 40.9%. Only 34.5% were classified as sufficient (≥30 ng/mL). The study found higher prevalence among non-Hispanic Black Americans, winter season, and ages 20-29 (paradoxically, due to lower supplement use and higher obesity in younger cohorts).\n"
    },
    {
      "url": "https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/",
      "title": "Vitamin D - Health Professional Fact Sheet",
      "publisher": "NIH Office of Dietary Supplements",
      "source_type": "govt_report",
      "statistic": "5% of US population at risk of deficiency (<30 nmol/L); 18.3% at risk of inadequacy (30-49 nmol/L) per 2011-2014 NHANES; 28% take vitamin D supplements",
      "excerpt": "\"In 2011-2014, 5.0% of the population aged 1 year and older were at risk of vitamin D deficiency, and 18.3% were at risk of inadequacy. Approximately 28% of all individuals aged 2 years and older took a dietary supplement containing vitamin D.\"\n",
      "source_date": "2024-08-15",
      "source_accessed": "2026-04-26",
      "archive_url": "http://web.archive.org/web/20260424200650/https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/",
      "calculation_notes": "The NIH ODS fact sheet reports NHANES 2011-2014 using the stricter IOM threshold (<30 nmol/L = <12 ng/mL) for \"at risk of deficiency\" and 30-49 nmol/L (12-19 ng/mL) for \"at risk of inadequacy.\" Combined, 23.3% fall below 20 ng/mL by the broader clinical convention. Critically, 72% of US adults do NOT take vitamin D supplements, meaning the deficiency burden falls disproportionately on this majority. The 92% of men and 97%+ of women who get less than the EAR from food alone underscores how dependent adequate status is on either supplementation or sustained sun exposure.\n"
    },
    {
      "url": "https://www.sciencedirect.com/science/article/abs/pii/S0271531710002599",
      "title": "Prevalence and correlates of vitamin D deficiency in US adults",
      "publisher": "Nutrition Research (Forrest & Stuhldreher)",
      "source_type": "peer_reviewed",
      "statistic": "Overall vitamin D deficiency prevalence 41.6%; non-Hispanic blacks 82.1%, Hispanics 69.2%",
      "excerpt": "\"The overall prevalence rate of vitamin D deficiency was 41.6%. The highest rate was seen in blacks (82.1%), followed by Hispanics (69.2%).\"\n",
      "source_date": "2011-01-01",
      "source_accessed": "2026-04-26",
      "archive_url": "http://web.archive.org/web/20240624051821/https://www.sciencedirect.com/science/article/abs/pii/S0271531710002599",
      "calculation_notes": "Forrest & Stuhldreher analysis of NHANES 2005-2006 data (n = 4,495). Deficiency defined as serum 25(OH)D ≤20 ng/mL. The 41.6% figure is the most-cited prevalence estimate and is higher than the 2001-2018 pooled figure (24.6%) partly due to different assay methods and partly because the later pooled study used standardised calibration. The racial disparity (82.1% in Black Americans vs ~20% in non-Hispanic whites) is one of the largest in nutritional epidemiology, driven primarily by melanin-mediated reduction in cutaneous vitamin D3 synthesis.\n"
    }
  ],
  "comparison_anchors": [
    {
      "label": "Depression (lifetime, US adult)",
      "lifetime_us_adult": 0.2
    },
    {
      "label": "Kidney stones (lifetime, US adult)",
      "lifetime_us_adult": 0.11
    },
    {
      "label": "Type 2 diabetes (lifetime, US adult)",
      "lifetime_us_adult": 0.33
    }
  ],
  "personal_factor_multipliers": [
    {
      "factor": "dark skin pigmentation",
      "multiplier": 3.5,
      "notes": "NHANES 2005-2006: 82.1% deficiency in non-Hispanic Blacks vs ~20% in non-Hispanic Whites (~4x ratio); NHANES 2011-2014: 17.5% vs 2.1% (~8x at stricter threshold). Melanin reduces cutaneous vitamin D3 synthesis by up to 99% at equivalent UV exposure. A 3.5x multiplier is conservative across thresholds."
    },
    {
      "factor": "northern latitude (>37°N year-round)",
      "multiplier": 1.8,
      "notes": "Above 37°N latitude, UVB intensity is insufficient for cutaneous vitamin D synthesis during winter months (November-February). NHANES data show higher deficiency prevalence in northern states, and European studies at 50-55°N find ~55-59% deficiency in older adults."
    },
    {
      "factor": "elderly (65+)",
      "multiplier": 1.5,
      "notes": "Ageing skin produces ~75% less vitamin D3 than young skin at equivalent UV doses (Holick 2007). NHANES shows 14.8-17.4% deficiency in 65+ cohorts. The Endocrine Society 2024 guideline specifically recommends empiric supplementation for adults over 75."
    },
    {
      "factor": "obese (BMI ≥30)",
      "multiplier": 1.7,
      "notes": "Vitamin D is sequestered in adipose tissue, reducing bioavailability. NHANES 2001-2018: obesity was a significant independent predictor of deficiency. Wortsman et al. (2000) showed obese individuals had 57% lower serum 25(OH)D after equivalent UV exposure."
    }
  ],
  "short_label": "Vitamin D gap",
  "myth_framing": "underrated",
  "outcome_severity": "moderate_harm",
  "exposure_pattern": "cumulative",
  "outcome_type": "chronic_illness",
  "valence": "negative",
  "caveats": "\"Vitamin D deficiency\" means different things depending on where the threshold is drawn. The IOM uses <12 ng/mL (30 nmol/L) for frank deficiency risk; the Endocrine Society historically used <20 ng/mL (50 nmol/L); some practitioners treat <30 ng/mL as \"insufficiency.\" At the IOM cutoff, only ~5% of the US population qualifies. At the Endocrine Society cutoff, ~24%. At the insufficiency line, ~65%. This entry uses the Endocrine Society's <20 ng/mL threshold as the clinically meaningful boundary, since it corresponds to the level below which parathyroid hormone rises and bone metabolism is demonstrably impaired. Subclinical insufficiency (20-29 ng/mL) is far more common but its clinical consequences remain debated -- the 2024 Endocrine Society guideline notably stepped back from routine population screening. Latitude, season, skin colour, body composition, and indoor lifestyle interact multiplicatively, making population averages particularly poor predictors of individual status.\n",
  "quality_score": {
    "d1": 4,
    "d2": 5,
    "d3": 4,
    "d4": 4,
    "d5": 5,
    "d6": 5,
    "d7": 5,
    "d8": 5,
    "avg": 4.625,
    "scored_by": "extracted-from-transcript",
    "scored_at": "2026-04-26",
    "methodology_version": "1.0"
  },
  "reviewer": "quality-review-agent",
  "last_reviewed": "2026-04-26",
  "reviewed": true,
  "generated_at": "2026-04-26",
  "image": {
    "alt": "A single ray of sunlight passing through a window onto a bare forearm, flat vector illustration in muted gold and grey tones."
  },
  "attribution": "Likelier — https://likelier.app",
  "license": "https://creativecommons.org/licenses/by-sa/4.0/",
  "support": "https://buymeacoffee.com/kgluszczyk?via=likelier&utm_content=api-fear-single",
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}