In 2004, a federal health survey finished drawing blood from thousands of American adults. Researchers later asked that blood a simple question. How many of these people were low on vitamin B12?
The answer was 3 percent. The answer was also 26 percent.
Same survey, same years, same people. The National Institutes of Health Office of Dietary Supplements prints both figures on its vitamin B12 fact sheet. The only difference between them is the cut point, the blood concentration below which a result gets called low. Below 200 picograms per milliliter, 3 percent of adults aged 19 and older came up short. Below 350, 26 percent did.
Nobody’s health changed between those two numbers. A line moved.
Most of what you will read about nutrient deficiency in America is a figure like one of those, reported without the line that produced it. Here is how the measuring works, what the federal data show, and why a lab result is the start of a conversation rather than the end of one.
The federal source of record changed in June 2026
For fourteen years, the standard American reference on nutrient status was the Second National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population, published by the Centers for Disease Control and Prevention in 2012. It covered 58 biomarkers, drawn from survey years 2003 to 2006.
On June 24, 2026, CDC released its replacement. The 2026 National Nutrition Report covers 131 biomarkers and spans the National Health and Nutrition Examination Survey, known as NHANES, from 1999-2000 through August 2021 to August 2023. That is roughly 24 years of blood and urine from a sample built to represent the country.
The growth tells its own story. The peer-reviewed companion paper by Christine Pfeiffer and colleagues, published in Current Developments in Nutrition in April 2026, records that the earliest editions carried 27 biomarkers for 1999-2002 and 58 for 2003-2006.
It is not a CDC-only product either. Author affiliations on that paper span four CDC centers, FDA’s Human Foods Program and the NIH Office of Dietary Supplements.
If something you are reading cites the 2012 report as the current picture of American nutrition, it is working from measurements taken up to twenty years ago.
What CDC says its own numbers can and cannot do
Here is the part that rarely travels with the headlines.
For most indicators, the 2026 report does not publish a deficiency rate at all. It publishes a reference interval: the central 95 percent of values, from the 2.5th percentile to the 97.5th, in a population NHANES assumes to be generally healthy. Results outside that band get treated as unusual. Unusual is not the same as unhealthy, and CDC does not claim otherwise.
The report’s introduction is direct about the limit. On the question of which biomarker concentrations signal risk for disease and which are of negligible health concern, CDC says more research is needed, then adds: “This is beyond the scope of this report.”
Three further cautions sit in the same document, and each cuts against a common way these numbers get used. Differences between population subgroups, CDC writes, do not necessarily imply health status problems. Observed differences should not always be read as causal. And comparing one survey cycle with another over time calls for caution, because each cycle is a fresh cross-section of a changing country, not the same people followed forward.
So the flagship federal report on American nutritional biomarkers declines, deliberately, to tell you who is deficient. A confident claim about national deficiency rates is doing something its own data source says it was not built to do.
Where deficiency in the United States is documented
Some of it is well documented. The evidence is strongest where a specific population, a specific marker and a specific threshold line up.
Iodine, especially during pregnancy
This is the one most likely to surprise an American reader.
The Office of Dietary Supplements reports a median urinary iodine concentration of 164 micrograms per liter for the general population aged 6 and older in NHANES 2007-2008, which clears the World Health Organization benchmark of more than 100 for a population of nonpregnant adults. Women of reproductive age sat lower, at a median of 119 in NHANES 2007-2014.
Pregnancy is where it tightens. WHO treats a population median of 150 to 249 micrograms per liter as adequate during pregnancy, and values under 150 as insufficient. ODS reports medians for pregnant women in the United States of 181 in 2003-2004, 153 in 2001-2006, 125 in 2005-2008 and 144 in 2007-2014. Three of those four sit at or below the threshold. ODS concludes that a substantial portion of pregnant women in this country are iodine insufficient.
CDC’s 2026 report arrives in the same place from newer data, describing borderline mild iodine deficiency among women of reproductive age in the more recent survey cycles, with urine iodine lower in 2017-2018 than in 2001-2002. Two federal sources, different data vintages, same direction.
One caution travels with all of it. A urinary iodine median describes a population, not a person, because urinary iodine moves with what someone ate in the past day. Article 333 covers iodine in depth.
Iron in pregnancy
ODS reports that 18 percent of pregnant women had iron deficiency in NHANES 1999-2006, and that the figure climbs across the pregnancy: 6.9 percent in the first trimester, 14.3 percent in the second, 29.7 percent in the third.
The fact sheet also breaks out depleted iron stores among pregnant women by race and ethnicity, at 23.6 percent for Mexican American women, 29.6 percent for non-Hispanic Black women and 13.9 percent for non-Hispanic White women. ODS does not restate survey years in that sentence, so read those three figures as published values rather than as a current measurement.
Folate, the deficiency the country mostly engineered away
In 1998 the United States began requiring folic acid fortification of enriched grain products. CDC’s 2026 release describes the before and after: about 10 to 12 percent of women of reproductive age previously did not have enough folate in their bodies, and that figure has since dropped to under 1 percent. Blood folate rose by roughly 50 percent across the population.
CDC gives those percentages without survey years attached, so read them as a before-and-after contrast rather than as dated measurements. ODS, on its own page, calls frank folate deficiency rare in the United States and reports that neural tube defect rates have declined by 28 percent since mandatory fortification began.
This is the clearest case in American nutrition of a measured deficiency, a policy response, and a measured change afterward.
Vitamin D is moving in two directions at once
The most interesting number in the 2026 report has not reached consumer coverage.
Among people aged 6 and older, comparing 2001-2002 with August 2021 to August 2023, CDC found that vitamin D insufficiency, defined there as 25-hydroxyvitamin D below 50 nanomoles per liter, fell from 28 percent to 22 percent.
Over exactly the same period, excess, defined as above 125 nanomoles per liter, rose from under 1 percent to 8 percent. CDC reports that the increase was largest in adult supplement users, in females, and in non-Hispanic White persons.
Low readings fell by six percentage points. High readings rose roughly eightfold. Both happened at once, across the same 22 years, and a single national summary figure hides one of them.
Supplement use is the obvious context, though CDC presents the comparison as descriptive rather than causal. In NHANES 2017 through March 2020, 60 percent of adults and nearly 35 percent of children and adolescents reported taking at least one supplement in the previous 30 days. CDC found vitamin biomarker levels typically higher in supplement users, with the largest differences for vitamin B6 and vitamin D status, while trace elements and minerals were mostly comparable.
What a high reading means, and what the published upper intake limits are, belongs to article 323. The point to carry here is narrower: a national nutrient pattern can improve and worsen simultaneously, in different people.
A measured difference, and a meaning that is not settled
CDC’s 2026 report found the greatest vitamin D deficiency among non-Hispanic Black persons. It also found that race and Hispanic origin differences were smaller in August 2021 to August 2023 than they had been in 2001-2002.
That is a measurement, and it is sound. What it means is a separate question, and the federal government’s own nutrient reference answers it carefully.
ODS states that Black Americans typically have lower serum 25-hydroxyvitamin D than White Americans, and then says this about the consequences: “whether these lower levels in persons with dark skin have significant health consequences is not clear.”
The page sets out why it puts it that way. People of African American ancestry have lower rates of bone fracture and osteoporosis than White Americans. Bone mineral density, bone mass and fracture risk track serum 25-hydroxyvitamin D in White and Mexican Americans, but that correlation is not seen in Black Americans. And ODS reports that the bone health of older Black American women does not appear to benefit from raising serum levels above 50 nanomoles per liter. Body fat, skin pigmentation and genetic variation in vitamin D binding protein are among the contributing factors it names.
Both federal statements are correct, and they have to be read together. The measured difference is real. The health conclusion a reader would naturally draw from it has not been established, and ODS says so in plain words. Reporting the CDC figure on its own implies something neither agency has concluded.
A wider version of the same caution sits on that page. ODS states that the serum concentrations associated with vitamin D deficiency have not been definitively identified, and that optimal concentrations for bone and general health have not been established. It also notes that the Endocrine Society has not identified concentrations associated with sufficiency, insufficiency and deficiency, and does not recommend routine testing in healthy individuals.
That society’s 2024 clinical practice guideline, published in the Journal of Clinical Endocrinology and Metabolism, reached the same place from the trial evidence. Its panel found no trial evidence supporting routine screening in the general population, including in people with obesity or dark complexion, and no clear evidence defining an optimal target level for disease prevention. The panel adds that its guideline was not designed to replace the Dietary Reference Intakes for vitamin D, so this is a gap in the evidence rather than a rival standard. Article 327 covers vitamin D as a nutrient.
The deficiencies that are rare here despite heavy marketing
Several nutrients sold hard in the United States have very little documented deficiency in it.
ODS calls frank vitamin A deficiency rare in the United States, and reports that fewer than 1 percent of the population had serum retinol below 20 micrograms per deciliter in NHANES 2003-2006 data. It describes selenium deficiency as very rare in the United States and Canada, and clinically significant vitamin K deficiency in adults as very rare.
Two entries need their scope read carefully. On vitamin C, ODS says deficiency and scurvy are rare in developed countries, not the United States specifically, and gives no US prevalence figure at all. On thiamin, ODS says beriberi is rare in the United States and other developed countries, then states that no current data on rates of thiamin deficiency in the US population are available. Rare and unmeasured are different claims, and the page makes both.
Chromium is the strangest entry in the set. ODS reports that chromium deficiency has not been reported in healthy populations, that no definitive deficiency symptoms have been established, and that no validated method for determining chromium status and no clinically defined chromium deficiency state exist. Chromium nonetheless carries a Daily Value of 35 micrograms on FDA’s current labeling table, so American supplement panels print a percentage next to a nutrient with no defined deficiency state and no validated test. Article 324 explains what that percentage is.
What a blood test for a nutrient does not measure
Most of the markers people ask for were built for clinicians working a case, not for individuals checking a score.
Magnesium. ODS states that no current data on magnesium status in the United States are available. The reason is mechanical. Most magnesium sits inside cells and in bone, under 1 percent circulates in serum, and that fraction is held under tight control, so serum levels do not accurately reflect total body magnesium. The widely repeated line that 48 percent of Americans do not get enough magnesium comes from the same ODS page, but it is an intake figure from NHANES 2013-2016 measured against the Estimated Average Requirement. An intake below a reference value is not a deficiency, and ODS says on that same page that no status data exist to check it against. Article 322 explains what the Estimated Average Requirement is for.
Zinc. ODS notes that serum zinc varies with sex, age, the time of the blood draw and infection, that it does not always track dietary or supplemental intake, and that both serum and plasma measures have important limitations. The NHANES 2011-2014 figures ODS reports, 3.8 percent of children under 10, 8.6 percent of males aged 10 and older and 8.2 percent of females below the sufficiency cutoff for their age and sex, rest on cutoffs an expert panel built from a statistical definition.
Vitamin d. ODS states that a finding can be falsely low or falsely high depending on the assay used and the laboratory. An international standardization program exists precisely because results were not comparable across laboratories.
Iron. Hemoglobin and hematocrit are the most commonly used screening measures, and ODS describes them as neither sensitive nor specific. It calls serum ferritin the most efficient and cost-effective test for diagnosing iron deficiency, with a concentration below 30 micrograms per liter suggesting deficiency, but it also notes that inflammation, including from infectious disease, can raise serum ferritin. The same ferritin number means different things depending on what else is happening in the body. Article 330 handles ferritin properly.
Vitamin B12. Most laboratories treat values below 200 or 250 picograms per milliliter as subnormal, and ODS says the cutoff between normal and deficient varies by method and laboratory. Serum methylmalonic acid is described as among the most sensitive markers of B12 status, but it rises with reduced kidney function and tends to run higher in older adults. Homocysteine, ODS says, has poor specificity, because other things move it.
That is the 3-versus-26 problem again, stated as biochemistry rather than statistics. These are clinician tools, read in clinical context.
Questions worth asking before a result changes anything
If a nutrient result comes back flagged, these questions decide what it means. They are written for a conversation with a clinician, not for interpreting the number yourself.
- Which cut point did this laboratory use, and would another one use a different number? ODS says the B12 cutoff varies by method and laboratory, and that a vitamin D result can read falsely high or falsely low depending on the assay.
- Does this marker reflect stores, or recent intake? Urinary iodine tracks the past day or so. Ferritin reflects stores. Serum magnesium reliably reflects neither.
- Is anything else moving this number right now? Inflammation and infection raise ferritin. Reduced kidney function raises methylmalonic acid and homocysteine. The time of the blood draw affects serum zinc.
- Is there a second, confirming marker, and is running it worth the trouble?
- What decision would change if the number were different? If nothing changes either way, the test was not answering a question.
Some situations warrant a clinician’s attention rather than a search engine’s, and they are specific. Pregnancy or planning a pregnancy, given the iodine and iron patterns above. A diagnosed condition that limits fat absorption, which ODS names as a vitamin D risk group alongside gastric bypass surgery. The groups ODS lists for B12: older adults, people with pernicious anemia, people with celiac disease or Crohn’s disease, people who have had gastrointestinal surgery, people following vegetarian diets, and infants of mothers following vegan diets. New unexplained symptoms arriving with an out-of-range result, which is a clinical question rather than a nutritional one. And any prescription medication in the picture, because interactions are their own subject, covered in article 677.
What to carry away from a deficiency statistic
Before you believe a deficiency percentage, ask for three things: the cut point, the survey years, and the marker. Swap the cut point, shift the survey window or switch the marker, and the percentage moves with it. That is not a flaw in the science. It is what the science is doing.
Then hold the government’s own caution next to any figure quoted from its data. CDC measured 131 biomarkers across 24 years, published the result in June 2026, and wrote in its introduction that working out which concentrations carry disease risk is beyond what the report sets out to do. If the agency holding the blood samples will not draw that line, a figure quoted without its cut point has not earned the authority it borrows.
Sources
- Centers for Disease Control and Prevention. “2026 National Nutrition Report: At A Glance.” cdc.gov
- Centers for Disease Control and Prevention. “2026 National Nutrition Report: Introduction.” cdc.gov
- Centers for Disease Control and Prevention. “CDC Releases 2026 National Nutrition Report.” cdc.gov
- National Institutes of Health, Office of Dietary Supplements. “Vitamin B12: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Vitamin D: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Iodine: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Iron: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Folate: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Magnesium: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Zinc: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Chromium: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Vitamin A and Carotenoids: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Selenium: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Thiamin: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Vitamin C: Fact Sheet for Health Professionals.” ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. “Vitamin K: Fact Sheet for Health Professionals.” ods.od.nih.gov
- U.S. Food and Drug Administration. “Daily Value on the Nutrition and Supplement Facts Labels.” fda.gov
- PubMed. “Pfeiffer CM et al. "Centers for Disease Control and Prevention's 2026 Nutrition Report Presents Data for 131 Biomarkers from the Cross-Sectional National Health and Nutrition Examination Survey (NHANES 1999-August 2023)." Current Developments in Nutrition, 2026;10(5):107688. PMID 42163864. DOI: 10.1016/j.cdnut.2026.107688.” doi.org
- PubMed. “Demay MB et al. "Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline." Journal of Clinical Endocrinology and Metabolism, 2024;109(8):1907-1947. PMID 38828931. DOI: 10.1210/clinem/dgae290.” doi.org