Nutrient Deficiency in America (2026): CDC Blood Test Data
Based on CDC NHANES blood biomarker data from 8,360+ American adults:
- 22.1% are vitamin D deficient (serum 25(OH)D <50 nmol/L)
- 3.5% have depleted iron stores (ferritin <12 ng/mL) — 6.2% of women
- 3.6% are B12 deficient — 3.7% of adults 60 and older (NIH ODS, NHANES 2007–2018)
- 19% have suboptimal magnesium — blood tests miss most cases
- 0.2% are folate deficient — thanks to mandatory fortification
This page presents every data point from our NHANES analysis. All numbers are survey-weighted to represent the full US adult population.
Overview: Deficiency at a Glance
| Nutrient | Biomarker | Deficiency Cutoff | Deficient (%) | Insufficient (%) | Sample Size |
|---|---|---|---|---|---|
| Vitamin D | Serum 25(OH)D | <50 nmol/L | 22.1% | 58% | 5,225 |
| Iron | Serum Ferritin | <12 ng/mL | 3.5% | 13.7% | 8,360 |
| Folate | Serum Total Folate | <6.8 nmol/L | 0.2% | 4.7% | 5,250 |
| Vitamin B12 | Serum Vitamin B12 | <200 pg/mL | 3.6% | 12.5% | NHANES 2007-2018, adults 19+ |
| Magnesium | Serum Magnesium | <1.7 mg/dL | 2.5% | 19% | ~15000 |
Vitamin D Deficiency
By Age Group
| Age Group | Deficient (%) | Insufficient (%) | Sample Size |
|---|---|---|---|
| 18-30 | 32.6% | 75.8% | 1,042 |
| 31-50 | 26.2% | 67.5% | 1,491 |
| 51-65 | 17.1% | 49.3% | 1,455 |
| 65+ | 9.3% | 32.8% | 1,237 |
By Sex
| Sex | Deficient (%) | Insufficient (%) | Sample Size |
|---|---|---|---|
| Male | 23.4% | 63.6% | 2,519 |
| Female | 20.8% | 52.9% | 2,706 |
See our complete vitamin D guide for details, dosage guide, and D2 vs D3 comparison.
Iron Deficiency
By Age Group
| Age Group | Deficient (%) | Insufficient (%) | Sample Size |
|---|---|---|---|
| 18-30 | 5% | 18.8% | 1,665 |
| 31-50 | 5.4% | 18.2% | 2,511 |
| 51-65 | 1.8% | 7.6% | 2,283 |
| 65+ | 0.6% | 8.6% | 1,901 |
By Sex
| Sex | Deficient (%) | Insufficient (%) | Sample Size |
|---|---|---|---|
| Male | 0.6% | 4% | 4,058 |
| Female | 6.2% | 22.8% | 4,302 |
By Age and Sex (Where It Matters Most)
| Group | Deficient (%) | Insufficient (%) | Sample Size |
|---|---|---|---|
| Women 18-30 | 9.5% | 35.7% | 852 |
| Women 31-50 | 10.5% | 32.9% | 1,338 |
| Women 51-65 | 2.7% | 10.7% | 1,189 |
| Women 65+ | 0.5% | 9.5% | 923 |
| Men 18-30 | 0.6% | 2.3% | 813 |
| Men 31-50 | 0.3% | 3.4% | 1,173 |
| Men 51-65 | 0.8% | 4% | 1,094 |
| Men 65+ | 0.7% | 7.5% | 978 |
Key insight: Iron deficiency is overwhelmingly a women's health issue during reproductive years. Women ages 18-50 have deficiency rates about 16 to 35 times higher than men of the same age, driven by menstrual blood loss. After menopause (51+), the gender gap narrows dramatically. See our iron supplement form comparison and heavy periods guide.
Folate Deficiency
| Age Group | Deficient (%) | Insufficient (%) | Sample Size |
|---|---|---|---|
| 18-30 | 0.1% | 5% | 1,252 |
| 31-50 | 0.3% | 5.2% | 1,863 |
| 51-65 | 0.2% | 5% | 1,173 |
| 65+ | 0.2% | 2.8% | 962 |
Key insight: At just 0.2% deficiency, folate is a public health success story. However, 4.7% are in the insufficient range. Women planning pregnancy should talk to their provider about folate.
Vitamin B12 Deficiency
| Age Group | Deficient, <200 pg/mL (%) | Below 300 pg/mL (%) |
|---|---|---|
| All adults 19+ | 3.6% | 12.5% |
| 60+ | 3.7% | 12.3% |
Key insight: Serum deficiency barely moves with age in the survey data (3.7% at 60+ against 3.6% overall), even though absorption of food-bound B12 declines, which is why NIH tells adults over 50 to get most of their B12 from fortified food or a supplement. The people who test low usually have a cause: metformin, acid-suppressing drugs, a vegan diet, pernicious anemia or gut surgery. Full breakdown on the B12 deficiency page.
Magnesium Deficiency
| Measure | Prevalence |
|---|---|
| Clinically deficient (serum <1.7 mg/dL) | 2.5% |
| Suboptimal (serum <2 mg/dL) | 19% |
| Below RDA intake (dietary surveys) | ~50% |
Key insight: Magnesium is the nutrient where blood tests are most misleading. Only 0.3% of body magnesium is in the blood, so serum levels stay "normal" until severe depletion. The 2.5% clinical deficiency rate masks a far larger problem: roughly half of Americans do not meet the RDA through diet. See our complete magnesium guide and deficiency signs page.
Methodology
This data comes from the CDC National Health and Nutrition Examination Survey (NHANES), the gold standard for nutritional status assessment in the United States.
- Population: US civilian non-institutionalized adults aged 18+
- Data files: NHANES 2017-March 2020 Pre-Pandemic combined cycles
- Weighting: Survey-weighted using WTMECPRP for nationally representative estimates
- Vitamin D, iron, folate: Direct NHANES lab analysis (survey-weighted)
- B12: NIH Office of Dietary Supplements fact sheet, reporting an NHANES 2007–2018 analysis (adults 19+ and 60+). Magnesium: published analyses of NHANES data (serum magnesium is not in the 2017+ lab files)
- Total sample: 8,360+ adults with blood biomarker data
Data files used: P_DEMO.XPT, DEMO_J.XPT, VID_J.XPT, P_FERTIN.XPT, P_FOLFMS.XPT
How to Use This Data
- If you're a researcher or writer: This data is freely available for citation. Link back to this page as the source.
- If you want to test your levels: Vitamin D and iron (ferritin) are the most actionable blood tests. Ask your doctor for a 25(OH)D and ferritin test.
Frequently Asked Questions
How common is vitamin D deficiency?
Based on CDC NHANES blood data, 22.1% of US adults are vitamin D deficient (25(OH)D below 50 nmol/L / 20 ng/mL). Including insufficiency, 58% have suboptimal levels. Adults 18-30 are at highest risk (32.6% deficient). See our vitamin D deficiency signs page.
Who is most at risk for iron deficiency?
Women of reproductive age, especially ages 31-50 (10.5% deficient). Women overall are 10x more likely to be iron deficient than men. See our iron supplement guide.
Are blood tests reliable for all nutrients?
Vitamin D and iron (ferritin) blood tests are reliable and actionable. Folate and B12 serum tests are reasonably reliable. Magnesium blood tests are NOT reliable — serum magnesium reflects only 0.3% of body stores. You can be significantly magnesium-depleted with "normal" blood levels. This is why dietary intake surveys show ~50% inadequacy while blood tests show only 2.5% deficiency.
Why is folate deficiency so rare?
In 1998, the US mandated folic acid fortification of enriched grain products (bread, pasta, cereals). This public health intervention reduced folate deficiency from ~16% to under 1%. It remains one of the most successful nutrient fortification programs in history. However, women planning pregnancy should talk to their provider about folate.
Where does this data come from?
CDC NHANES (National Health and Nutrition Examination Survey) — the most comprehensive nutritional assessment of the US population. We analyzed the 2017-March 2020 pre-pandemic combined data files using survey weights for nationally representative estimates. B12 figures are the NIH Office of Dietary Supplements' reported NHANES 2007–2018 analysis; magnesium figures come from published analyses of NHANES data.
Related Pages
- Vitamin D Guide — D2 vs D3, dosage, K2 pairing
- Iron: Ferrous Sulfate vs Bisglycinate — The form matters
- Magnesium Guide — All 8 forms compared
Sources
- CDC National Center for Health Statistics. "National Health and Nutrition Examination Survey (NHANES) 2017-March 2020 Pre-Pandemic Data Files." cdc.gov/nchs/nhanes
- NHANES Laboratory Data Files: P_DEMO.XPT, VID_J.XPT, P_FERTIN.XPT, P_FOLFMS.XPT. NHANES Data Search
- NIH Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals (NHANES 2007–2018 prevalence). ods.od.nih.gov
- Rosanoff A, et al. "Suboptimal magnesium status in the United States: are the health consequences underestimated?" Nutr Rev. 2012;70(3):153-164. PMID: 22364157