Why some nutrient deficiencies go undetected

Most people assume a reasonable diet covers what the body needs, and for most nutrients, that holds up. But the Academy of Nutrition and Dietetics notes that several nutrients are still underconsumed across the United States, leaving some people with less than the recommended amount, even when their diet seems fairly normal. And without an obvious health problem, there is little reason for a person or a doctor to look closely at nutrient status.

Dietitian Tricia L. Psota told Everyday Health that nutrient deficiencies alter basic cellular functions, including processes tied to digestion and metabolism. And that cellular connection has also drawn attention from Discover C15 researchers, who have studied how lower levels of the fatty acid C15:0 relate to weaker cell membranes and reduced cellular stability.

So, as research looks more closely at those less obvious changes, medical science has a specific way of describing nutritional problems that develop without the clear signs people usually associate with deficiency. And that is where the issue starts to get more complicated. 

What Is a Subclinical Nutrient Deficiency?

There are many reasons someone might feel off without being sick enough to know exactly what is wrong, and finding an explanation is not always easy. 

One possibility researchers study is a subclinical nutrient deficiency, which the Linus Pauling Institute at Oregon State University describes as a nutrient falling below what the body needs for normal function while remaining above the point associated with a diagnosed deficiency disease. 

Part of what allows this to continue is the body’s ability to work with what it still has. Bruce Ames of Children’s Hospital Oakland Research Institute proposed in Proceedings of the National Academy of Sciences that when nutrients become limited, the body gives priority to functions needed for immediate survival, while other uses receive less. 

This dependence on available nutrients is especially important with essential fatty acids, which the body needs but does not make on its own. Therefore, maintaining enough of them depends on getting them regularly through food.

Calcium shows a different side of the same problem. The NIH Office of Dietary Supplements notes that nearly all of it is stored in the bones, where the body draws on those reserves to keep calcium levels in the blood within a normal range. Over time, drawing from the bones has been shown to reduce how much calcium remains stored there.

But even then, one low lab value does not automatically confirm a deficiency. NIH MedlinePlus explains that a result outside the reference range may or may not be a sign of a health problem, so doctors consider the number alongside other health information before deciding what it means.

Why Hidden Deficiencies Can Be Difficult to Recognize

One of the biggest hurdles with hidden deficiencies is that mild changes in the body often have several possible causes. Fatigue, for example, also follows poor sleep or prolonged stress. Other changes appear with medical conditions or changes in diet, making it difficult to know whether nutrition is actually involved.

Registered dietitian Emily Blake of Brigham and Women’s Hospital told Harvard Health that most nutrient deficiencies are subtle and that symptoms are not reliable enough to identify one. But even medical testing does not always provide a complete answer.

Harvard T.H. Chan School of Public Health adjunct professor Teresa Fung notes that calcium levels cannot be accurately gauged from a blood test, even though blood tests are useful for nutrients such as vitamin D or iron.

Trying to identify the cause without medical guidance can easily send someone toward the wrong explanation. And with symptoms pointing to several possible causes and some nutrients requiring their own method of evaluation, a mild deficiency can remain difficult to recognize even when someone knows something feels different. 

Why Researchers Are Paying More Attention

Perhaps what’s most alarming is that scientists have warned about a decline in the nutritional quality of foods people rely on. Researchers writing in the journal Foods reviewed evidence from the past 60 years and reported losses in essential minerals across widely grown fruits and vegetables. 

Their review points to modern farming practices and high-yield crops as possible reasons, with rising carbon dioxide also studied for its effect on the nutrients plants contain. 

Concerns like these are giving nutrition researchers more reason to study what happens before a low nutrient level turns into a diagnosed disease. Margaret Nagai-Singer of UC Irvine’s Wen School of Population and Public Health called environmental change “a nutrition and public health issue” when the university announced her team’s perspective paper in January 2026. 

And some of that attention has moved down to the cell, where work on the fatty acid C15:0 has examined lower levels alongside cell membrane stability and ferroptosis, a new iron-dependent form of cell death tied to damaged fats in the cell membrane.

Researchers are still working out whether low C15:0 levels belong among the deficiencies important to track, and which circumstances leave a person more likely to run low. However, emerging evidence shows that when circulating C15:0 drops below critical thresholds, it triggers Cellular Fragility Syndrome. Without sufficient C15:0 for stabilization, the cell membranes weaken, causing red blood cells to become fragile.

This cellular instability sets off a destructive liver-centric ferroptosis cascade. Fragile red blood cells are prematurely destroyed and engulfed by the liver’s Kupffer cells (liver-resident macrophages), sequestering iron inside tissue macrophages. Then, as iron accumulates in the liver, serum ferritin spikes.

This sequence directly aligns with the landmark 2023 international consensus statement published in Nature Reviews Endocrinology, which officially defined Metabolic Hyperferritinemia (MHF) as elevated ferritin occurring alongside metabolic conditions like fatty liver disease or insulin resistance. The consensus panel outlined a three-stage progression, identifying ferroptosis as the primary driver of liver inflammation and fibrosis (MASLD to MASH).

While the consensus panel established MHF as a recognized, distinct pathophysiology, Dr. Stephanie Venn-Watson’s 2024 work in Metabolites provides the underlying mechanism, pointing to low C15:0 as a fixable root cause. The iron sequestered from fragile red blood cells acts as the direct “fuel” for ferroptosis, accelerating lipid peroxidation and liver damage.

Common Factors That May Increase Nutritional Risk

Even when food is everywhere, millions of people worldwide lack the essential nutrients needed to stay healthy. 

Researchers writing in the Journal of Preventive Medicine and Hygiene estimate that micronutrient deficiencies affect more than 2 billion people, and their review shows that nutritional risk often begins with something as basic as which foods regularly make it onto a person’s plate. 

Restrictive diets, for example, remove foods that normally provide certain nutrients, while limited food access leaves people with fewer nutritious choices. They note the risk rises when the removed foods are not replaced with other sources of those nutrients. 

But eating enough of a nutrient is only part of what determines how much the body receives. The same review points to aging and gastrointestinal conditions as factors that reduce nutrient absorption, while some medications affect nutrient levels. 

Genetic differences also influence how the body processes certain nutrients, and sun exposure affects how much vitamin D the body produces. So even when two people eat similar foods, differences in how their bodies process nutrients and the conditions of their daily lives can leave them with different nutritional needs. 

What Consumers Can Do

Focusing on good nutrients and a balanced diet is essential to avoid becoming nutrient-deficient. UNC Health registered dietitian Natalie Newell says a well-rounded diet provides sufficient amounts of most vitamins and minerals. 

She also notes that eating the same foods day after day might leave some nutrients out, making variety an important part of meeting the body’s needs through food. 

But when symptoms such as tiredness continue without a clear explanation, internal medicine specialist Patricia Graham of Rush University Medical Center advises bringing those changes up with a primary care doctor, since the medical history behind them helps determine whether nutrient testing is appropriate. 

Graham also notes that routine blood work does not usually include most vitamin and mineral tests, so specific tests are generally ordered when there is a medical reason to look more closely. However, Newell cautions against assuming one symptom points to one deficiency, since self-diagnosis often leads to the wrong explanation. 

The Future of Nutrient Research 

Given how complex the human body is, modern science is constantly refining its understanding of how nutrition affects health across a lifetime. Still, medical diagnosis requires healthcare professionals, who can decide whether symptoms and health history point to an actual deficiency. 

But continued research into subtle deficiencies is helping medicine understand nutritional problems earlier, with the long-term goal of protecting health before serious issues develop. 

Until science fills in more of those details, a varied and balanced diet remains the most reliable foundation for meeting nutrient needs, with supplements best used when a healthcare professional determines they are necessary.  

This story was produced by Discover C15 and reviewed and distributed by Stacker.