It’s easy to assume that eating enough means eating well. Someone can take in plenty of calories every day, never feel physically hungry, and still be running on empty at the cellular level. This condition even has a name in the scientific literature: “hidden hunger,” a state in which the body gets sufficient (or even excessive) energy but not enough of the specific vitamins and minerals it needs to function properly. It turns out to be far more common, and far more consequential, than most people realize.

A Problem Hiding in Plain Sight

Researchers draw a distinction between “nutritional inadequacy,” when intake falls below the estimated average requirement, and full-blown “nutritional deficiency,” when nutrient levels drop so low that the body can no longer perform its normal functions. The second condition produces clear clinical symptoms; the first often doesn’t; it can sit there for years, quietly raising the risk of chronic disease, before anyone notices anything is wrong.

Globally, micronutrient deficiencies are estimated to affect more than two billion people across every age group, with pregnant women and children under five at particular risk. They’re linked to roughly one in ten childhood deaths worldwide. And while the burden is heaviest in low- and middle-income countries, it isn’t confined to them: certain deficiencies show up reliably in specific subgroups of wealthy, food-abundant nations too, which is part of what makes this such a counterintuitive topic.

Measuring What’s Missing

Figuring out whether someone is actually deficient in a given nutrient is harder than it sounds. Researchers typically rely on two tools: nutritional biomarkers (blood, saliva, or urine tests measuring things like serum folate, vitamin D, or zinc) and dietary questionnaires. Both come with real limitations. Many nutrients are tightly regulated by the body’s own homeostatic mechanisms, so their circulating blood levels don’t always reflect what’s actually stored in tissues; iron status, for example, requires several different lab measurements combined, not just one. Dietary questionnaires, meanwhile, tend to be slow and not especially sensitive. Used together, though, the two approaches can offer a reasonably reliable picture of a population’s nutritional exposure.

When the Big Building Blocks Run Short

Most people think of “deficiency” in terms of vitamins and minerals, but shortfalls in macronutrients, protein, carbohydrates, and essential fats, can be just as serious.

• Protein-energy malnutrition is the most severe form, and it shows up mainly where food access is limited. It has two well-known faces: marasmus, near-total food deprivation that leaves the body reduced to skin and bone, and kwashiorkor, a condition marked by a swollen, fluid-retaining belly that develops when children are weaned onto carbohydrate-heavy diets without enough protein.
• Carbohydrate deficiency forces the body into gluconeogenesis, breaking down proteins and fats to make glucose for tissues like neurons that depend on it. Left unchecked for long enough, this produces ketosis, recognizable by its telltale sweet-smelling breath.
• Essential fatty acid deficiency (omega-3 and omega-6, which the body cannot make on its own) shows up as slowed growth in children, dry rashes, and slower wound healing. A lower omega-3 index has also been linked, in observational research, to a higher risk of dying from coronary heart disease.

The Long List of Micronutrients That Keep the Body Running

Beyond the macronutrients, the paper walks through a striking number of vitamins and minerals whose absence quietly undermines specific systems in the body.

• The fat-soluble vitamins (A, D, E, and K) each guard a distinct piece of physiology. Vitamin A deficiency, still common in developing countries, damages epithelial tissue and is a leading cause of preventable childhood blindness, the WHO estimates it affects 70 to 80 million children worldwide, often without obvious symptoms at first. Vitamin D deficiency undermines calcium and phosphorus absorption, producing osteomalacia in adults and rickets in children, and has been tied to immune dysfunction, hypertension, and insulin resistance. Vitamin E deficiency, though rarer, can cause ataxia and nerve damage over time. Vitamin K deficiency disrupts blood clotting and is serious enough in newborns to have its own clinical name, hemorrhagic disease of the newborn.
• The B vitamins and vitamin C are workhorses behind energy metabolism, nerve function, and tissue repair. B6 deficiency can trigger anemia and nerve problems; B12 deficiency, found almost exclusively in animal foods, puts strict vegans and their breastfed infants at particular risk; folate (B9) deficiency during pregnancy is strongly linked to neural tube defects, which is why prenatal supplementation matters so much. Vitamin C deficiency causes scurvy, historically a disease of sailors, still occasionally seen today in infants fed only cow’s milk.
• Key minerals round out the picture. Iron deficiency is the single most common nutritional deficiency worldwide, hitting young children and premenopausal women hardest, and produces the fatigue and paleness of anemia. Iodine deficiency impairs thyroid hormone production and, during pregnancy, can permanently affect a child’s neurological development; it’s the reason iodized salt became a public-health cornerstone. Zinc, magnesium, selenium, calcium, potassium, and fluoride each play narrower but still essential roles, from wound healing and immune defense to bone density and dental protection.

Who Is Most Likely to Be Affected

Deficiency risk isn’t evenly spread across a population. Infants and young children, pregnant and breastfeeding women, older adults, people following restrictive diets (vegan diets without B12 supplementation, or aggressive calorie-restricted diets for weight loss), and people with chronic alcohol use all show up repeatedly as higher-risk groups. So do people with underlying conditions that impair absorption, such as celiac disease or inflammatory bowel disease. The common thread isn’t a single cause but a combination: reduced intake, increased requirements, or a body that can’t properly absorb what it’s given.

Catching It Before Symptoms Appear

Because many deficiencies develop silently, screening matters. Blood, saliva, and urine-based biomarkers can now flag several nutrient shortfalls before clinical symptoms show up, and newer methods can even assess omega-3 fatty acid status from a simple blood draw. Broader indicators, like body mass index, total cholesterol, or hemoglobin, help clinicians spot general malnutrition risk, while validated dietary questionnaires offer a complementary, if more time-consuming, picture.

Filling the Gaps: The Role of Supplements

Perhaps the most sobering numbers in the whole field come from U.S. national nutrition data. Despite a food supply that’s often fortified and enriched, roughly 90% of American adults fall short of the estimated average requirement for vitamins D and E; around half fall short for vitamin A, calcium, and magnesium; and only a small minority meet recommended potassium and vitamin K intakes. This is happening in one of the wealthiest, most food-abundant countries in the world, a reminder that abundance of calories says nothing about adequacy of nutrients.

Multivitamin and multimineral supplements, used by roughly a third of U.S. adults, have been associated in several studies with measurably better micronutrient intake and a lower prevalence of shortfalls in nutrients like iron, magnesium, and vitamins A, C, D, and E, compared with diet alone. Researchers have gone so far as to suggest that improving diet quality across a population could prevent a meaningful share of deaths worldwide.

The Limits of What We Know

As with most nutrition science, the picture isn’t perfectly clean. Some biomarkers are poor proxies for what’s actually happening inside tissues, since the body tightly regulates blood levels of certain nutrients regardless of what’s stored. Dietary questionnaires remain imprecise. And many countries, lacking their own food composition databases, have to rely on data collected elsewhere, which introduces its own uncertainty. None of this undermines the core finding, deficiencies are common and consequential, but it’s a reminder that nutritional science is still refining its tools.

More Than Just Filling In the Blanks

The throughline across all of this research is that “eating enough” and “eating well” are two different things, and the gap between them is wider, and more widespread, than most people assume. Addressing it isn’t just about reaching for a multivitamin; it starts with understanding which nutrients a particular diet, life stage, or health condition tends to leave short, and building toward genuine adequacy from there, through food first, and supplementation where food alone isn’t closing the gap.

Disclaimer

The information provided in this article is for educational and informational purposes only and is not intended as medical advice, diagnosis, or treatment. For full scientific detail, precise data, and the original bibliography, please refer to the complete publication, available on PubMed.

Kiani AK, Dhuli K, Donato K, Aquilanti B, Velluti V, Matera G, Iaconelli A, Connelly ST, Bellinato F, Gisondi P, Bertelli M. Main nutritional deficiencies. J Prev Med Hyg. 2022 Oct 17;63(2 Suppl 3):E93-E101. doi: 10.15167/2421-4248/jpmh2022.63.2S3.2752. PMID: 36479498; PMCID: PMC9710417.