Vitamin deficiency: what are the dangers and how to recognize it

Vitamin deficiency is a form of "hidden hunger": a person may have enough calories, but not enough vitamins and minerals. International organizations estimate that billions of people worldwide consume insufficient amounts of key micronutrients, including vitamins A, D, B vitamins, C, and E, as well as iron, iodine, zinc, and calcium. [1]

This deficiency often occurs asymptomatically or with very vague complaints: fatigue, irritability, memory loss, brittle nails, hair loss. People attribute it to stress and age, although the underlying cause may be a deficiency of several vitamins at once. This condition is described as "hidden micronutrient deficiency." [2]

At the population level, vitamin deficiencies increase the incidence of infections, impair cognitive development in children, reduce productivity in adults, and contribute to the rise in cardiovascular and metabolic diseases. Vitamin A, iodine, and iron deficiencies are particularly prominent, and the World Health Organization considers them among the major global nutritional problems. [3]

It's important to understand that a deficiency in just one vitamin is rare. More often, a combination of mild deficiencies in several micronutrients is observed, which mutually reinforce each other. Research shows that a significant proportion of women of reproductive age and young children have at least one significant vitamin or mineral deficiency. [4]

The consequences of this condition aren't always immediately dramatic, but they are cumulative: immune defenses are weakened, bone quality deteriorates, the nervous system suffers, and the risk of pregnancy complications and the onset of chronic diseases increases. The conclusion is clear: vitamin deficiency isn't just about appearance, but also about overall health and life expectancy. [5]

Table 1. Variants of the body's vitamin status

State variant	Characteristic
Optimal provision	Adequate intake, good health
Latent deficiency	Mild biochemical abnormalities, minimal complaints
Subclinical deficiency	Clear laboratory signs, non-specific symptoms
Clinical deficit	Obvious symptoms and signs of specific hypovitaminosis
Combined deficiency	Simultaneous deficiency of several vitamins and minerals

Forms of deficiency: acute, chronic and subclinical

Classic textbook images of scurvy or severe rickets are less common today, but they clearly illustrate the consequences of severe, prolonged deficiency. A complete vitamin C deficiency leads to scurvy, bleeding gums, weakness, and vascular fragility. A vitamin D deficiency leads to impaired bone mineralization and skeletal deformities. [6]

In practice, chronic or subclinical deficiency is much more common. In this case, vitamin levels are slightly below optimal, and the body compensates for a while. The person experiences fatigue, mild depression, and decreased concentration, but none of the "classic" symptoms of the disease. However, research has linked such conditions to an increased risk of cognitive impairment, falls, and decreased quality of life. [7]

Deficiency can be primary or secondary. Primary deficiency is associated with a vitamin deficiency in the diet, such as restrictive diets, a poor selection, or overindulgence in refined foods. Secondary deficiency develops when a normal diet is present, but absorption or metabolism is impaired, such as intestinal and liver disease, long-term use of certain medications, or alcoholism. [8]

A separate possibility is a temporary deficiency due to increased need. This occurs during pregnancy, breastfeeding, intense exercise, and severe infections, when the body requires more vitamins for growth, tissue repair, and immune function. If the diet is not adjusted and supplements are not prescribed, reserves are quickly depleted and the deficiency becomes permanent. [9]

Finally, there's the concept of relative deficiency. While the vitamin is technically present in the blood and levels are within the "normal" range, this isn't enough for a specific individual or condition. For example, even "lower-normal" vitamin B12 levels are associated with slower cognitive processing and changes in white matter in the brain in the elderly. [10]

Table 2. Comparison of acute and chronic vitamin deficiencies

Parameter	Acute severe deficiency	Chronic subclinical deficiency
Speed of development	Fast, weeks or months	Slowly, over months and years
Symptoms	Bright, specific	Vague, non-specific
Diagnostics	Relatively simple	Requires laboratory and functional analysis
Effect on organs	Severe, sometimes irreversible	Cumulative, increases the risk of chronic diseases
Typicality in modern life	Rarely	Very often

Which systems are affected first?

The hematopoietic system is one of the first to react to vitamin deficiencies. Folate and vitamin B12 deficiencies disrupt DNA synthesis in bone marrow cells, leading to megaloblastic anemia. This causes weakness, shortness of breath during exertion, dizziness, pallor, and decreased performance. Iron is not technically a vitamin, but its deficiency closely correlates with folate deficiency and exacerbates the symptoms of anemia. [11]

The nervous system is sensitive to deficiencies of B vitamins and vitamin B12. B12 deficiency is associated with peripheral neuropathy, decreased leg muscle strength, balance problems, memory impairment, and even an increased risk of dementia. Thiamine deficiency leads to severe neurological syndromes, impaired coordination, and mental disorders, especially in the context of alcoholism. [12]

Bones and muscles suffer from vitamin D, calcium, and magnesium deficiencies. Vitamin D deficiency impairs calcium absorption in the intestines, reduces bone mineral density, and increases the risk of osteoporosis, fractures, and muscle weakness. Even moderate vitamin D deficiency is associated with an increased risk of falls in the elderly and bone and muscle pain in adults. [13]

The immune system also depends on adequate vitamin supply. Vitamin A maintains the integrity of mucous membranes and reduces the risk of severe infections in children, vitamin D modulates innate and adaptive immunity, and vitamins C and E protect immune cells from oxidative stress. Deficiencies of these vitamins increase the frequency and severity of respiratory and intestinal infections, and fatigue persists longer after illness. [14]

Skin, hair, and mucous membranes are a clear indicator of vitamin status. A deficiency of vitamin C and some B vitamins leads to inflammation and cracks at the corners of the mouth, dry skin, brittle hair, and impaired wound healing. Vitamin A deficiency causes xerosis of the skin, dry mucous membranes, and night blindness. These symptoms are often underestimated, although they serve as an early indicator of more serious disorders. [15]

Table 3. Body systems and typical consequences of vitamin deficiency

System	The most vulnerable vitamins	Typical consequences
Hematopoiesis	Folate, B12, B6, vitamin C	Anemia, weakness, shortness of breath
Nervous system	B1, B6, B12, folate	Neuropathies, cognitive impairment, depression
Bones and muscles	Vitamin D, vitamin K, calcium, magnesium	Osteoporosis, fractures, muscle weakness
Immune system	Vitamin A, vitamin D, vitamin C, B6	Frequent infections, severe course of diseases
Skin and mucous membranes	Vitamin A, vitamin C, B vitamins	Dryness, cracks, slow healing

Who is at risk: not only children and the elderly

Traditionally, vitamin deficiencies are thought of only in children and the elderly. Indeed, young children and pregnant women are particularly vulnerable to deficiencies of vitamin A, iron, iodine, and folate, which impact growth, nervous system development, and immunity. However, recent estimates indicate that deficiencies are also widespread among working-age adults, especially women. [16]

Women of reproductive age often experience deficiencies in iron, folate, B vitamins, and vitamin D. Causes include heavy menstrual periods, pregnancy and lactation, dieting, and low meat and fish consumption. All of this makes vitamin deficiency in women not only a medical issue but also a socioeconomic one: it reduces productivity and increases the risk of complications during pregnancy. [17]

Older adults are more likely to experience subclinical deficiencies of vitamin B12, vitamin D, folate, and certain minerals. Absorption is impaired, appetite is reduced, and the incidence of chronic diseases and polypharmacy, in which medications affect micronutrient metabolism, increases. Vitamin deficiency in this age group accelerates sarcopenia, impairs coordination, and increases the risk of falls and fractures. [18]

Vegetarians and especially vegans are at risk for vitamin B12 deficiency, as well as vitamin D, iron, zinc, and sometimes calcium, if their diet is poorly planned and fortified foods are not consumed. However, a person may appear to be fine for years until their liver B12 stores are depleted, leading to neurological and hematological symptoms. [19]

People with chronic diseases of the intestines, liver, pancreas, as well as those who have undergone surgery on the stomach and small intestine, often have a secondary deficiency of fat-soluble vitamins and B vitamins. Their standard diet does not ensure normal absorption, so without monitoring and targeted correction, the deficiency progresses even on the “right” diet. [20]

Table 4. Main risk groups for vitamin deficiency

Population group	The most common deficiencies
Preschool children	Vitamin A, vitamin D, iron, zinc
Women of reproductive age	Iron, folate, vitamin D, B vitamins
Pregnant and lactating women	Folate, iron, iodine, vitamin D
Elderly people	Vitamin B12, vitamin D, folate, zinc
Vegetarians and vegans	B12, vitamin D, iron, zinc, sometimes calcium
Patients with intestinal and liver diseases	Fat-soluble vitamins, B vitamins

From the first symptoms to severe illnesses: specific examples

Vitamin A deficiency is one of the most studied and dramatic examples. In childhood, it leads to night blindness, dry conjunctiva and cornea, and even keratomalacia and irreversible blindness. Children with vitamin A deficiency have a higher risk of death from measles and diarrheal infections, making prophylactic vitamin A supplementation an important part of public health programs in low-income countries. [21]

Vitamin D deficiency in children causes rickets, and in adults and the elderly, osteomalacia and accelerated bone loss. Vitamin D deficiency has been associated with an increased risk of fractures, overall mortality, and a number of autoimmune and infectious diseases, although direct causality has not been proven for all associations. [22]

Vitamin B12 and folate deficiency cause megaloblastic anemia, which manifests as severe weakness, shortness of breath, and pale skin and mucous membranes. B12 deficiency also causes neurological symptoms, including numbness and tingling in the extremities, gait disturbances, and cognitive decline. In older adults, even borderline low B12 levels are associated with slower information processing and an increased risk of dementia. [23]

Vitamin C deficiency initially manifests not with the classic symptoms of scurvy, but with milder symptoms. Fatigue, depressed mood, loss of appetite, vascular fragility, and a tendency toward microbleeds appear, wounds heal poorly, and gum bleeding increases. With prolonged, severe deficiency, scurvy proper develops, with severe weakness, pain, anemia, and a high risk of death. [24]

Niacin (vitamin B3) deficiency leads to pellagra, which is characterized by the triad of dermatitis, diarrhea, and dementia. Although classic pellagra is now rare, localized outbreaks are still reported in areas where diets are based almost exclusively on corn without fortification, as well as in individuals with severe alcoholism and malabsorption syndromes. [25]

Vitamin deficiencies can also manifest themselves in more subtle ways: increased blood pressure, worsening lipid profiles, decreased glucose tolerance, delayed cognitive development in children, and an increased risk of pregnancy complications. These effects are not always directly linked to a single vitamin, but the contribution of micronutrient deficiencies to these processes is increasingly being confirmed by research. [26]

Table 5. Examples of diseases associated with vitamin deficiency

Vitamin	Underlying disease with severe deficiency	Key manifestations
Vitamin A	Hypovitaminosis A	Night blindness, xerophthalmia, risk of blindness
Vitamin D	Rickets, osteomalacia	Bone deformation, pain, fractures
Vitamin B12	Megaloblastic anemia, neuropathy	Weakness, anemia, numbness, cognitive impairment
Folate	Megaloblastic anemia	Anemia, glossitis, pregnancy complications
Vitamin C	Scurvy	Bleeding gums, weakness, poor healing
Vitamin B3	Pellagra	Dermatitis, diarrhea, dementia

How deficiency is detected: symptoms, tests, diagnostic limitations

Diagnosis of vitamin deficiency relies on three pillars: complaints and examination, laboratory tests, and, if necessary, functional tests. Symptoms are rarely strictly specific, especially in the early stages: fatigue, decreased concentration, brittle nails, hair loss, and depressed mood. Therefore, it is difficult to make a diagnosis based solely on how you feel. [27]

Laboratory tests include measuring blood levels of specific vitamins, assessing associated markers, and assessing organ function. For vitamin D, 25-hydroxyvitamin D concentrations are determined; for vitamin B12, serum levels and sometimes methylmalonic acid; for folate, serum or red blood cell levels. Additionally, hemoglobin, ferritin, bone turnover parameters, and other parameters are assessed depending on the clinical situation. [28]

However, no single method provides a definitive answer. Blood vitamin levels are affected by inflammation, concomitant illnesses, medications, and even the time of year. Biochemical deficiencies can precede clinical symptoms, and in some people, symptoms appear before the level falls outside the reference range. Therefore, diagnosis is usually based on a combination of several criteria. [29]

Population-based screening programs often target at-risk groups rather than specific vitamins. For example, a number of countries recommend routinely assessing vitamin D levels in the elderly, vitamin B12 levels in people with anemia or neurological symptoms, and iron and folate levels in pregnant women and women with heavy menstrual bleeding. This approach allows for the detection of deficiencies before the development of severe complications. [30]

It's important to remember that a diagnosis of vitamin deficiency isn't just a test result, but also the answer to the question of why it occurred. Without dietary adjustments, treatment of gastrointestinal diseases, lifestyle changes, and, if necessary, drug therapy, the deficiency will return as soon as supplementation is stopped. [31]

Table 6. Frequently used laboratory markers for suspected vitamin deficiency

Suspected shortage	Basic tests	Additional indicators
Vitamin D	Serum 25-hydroxyvitamin D	Calcium, phosphorus, parathyroid hormone
Vitamin B12 and folate	B12, serum folate, complete blood count	Methylmalonic acid, homocysteine
Vitamin A	Retinol in serum	Assessment of the condition of the cornea and retina
Vitamin C	Plasma ascorbic acid	Condition of gums, skin, wound healing
General micronutrition status	Food diary, extended biochemical profile	Minerals, protein, functional tests

Long-term consequences of vitamin deficiency

The most serious problem with vitamin deficiency is that its effects manifest not only now but also years later. Vitamin D and calcium deficiencies in youth increase the risk of osteoporosis and fractures in old age. Folate and B12 deficiencies in middle age can accelerate the accumulation of white matter damage in the brain and increase the risk of cognitive decline. [32]

Iron and B vitamin deficiencies in children reduce academic performance and impair attention and memory, which subsequently impacts educational attainment and economic opportunities. This is not only a medical problem but also a macroeconomic one: countries with high levels of "hidden hunger" lose percentages of their domestic product due to declining productivity. [33]

In women of reproductive age, chronic deficiencies of vitamin A, iodine, folate, iron, and vitamin D increase the risk of pregnancy complications, preterm birth, low birth weight, and neural tube defects. These consequences often become apparent after the window for prevention has been missed. [34]

For working adults, vitamin and mineral deficiencies lead to increased fatigue, a tendency toward depression and anxiety, decreased productivity, and more days off work. Research on "hidden hunger" shows that even moderate deficiencies contribute to the development of cardiovascular disease, type 2 diabetes, and certain types of cancer. [35]

Thus, vitamin deficiency is not just a short-term discomfort, but a factor that can significantly shorten the active period of life and increase the likelihood of severe chronic diseases. Correction of deficiencies is considered an important part of strategies for maintaining public health and reducing the burden of non-communicable diseases. [36]

Table 7. Long-term consequences of chronic vitamin deficiency

Direction	Possible consequences
Bones and joints	Osteoporosis, fractures, chronic pain
Brain and cognitive functions	Memory loss, dementia, depression
Cardiovascular system	Increased cardiovascular risk, hypertension
Reproductive health	Pregnancy complications, adverse fetal outcomes
Economic consequences	Decreased productivity, rising health care costs

Prevention and safe correction of deficiency

Prevention starts with your plate. A varied diet with daily inclusion of fruits and vegetables, whole grains, legumes, nuts, fish, and moderate amounts of animal products remains the most reliable way to prevent most vitamin deficiencies. Such a diet provides not only the vitamins themselves, but also minerals, protein, and protective phytochemicals. [37]

In a number of countries, food fortification programs are being used to combat widespread deficiencies of folate, iodine, vitamin A, and vitamin D: iodized salt, flour fortified with folate, margarines, and milk with added vitamin D. This allows for increased vitamin intake among the entire population without radically changing eating habits. [38]

Individual vitamin supplements are needed when, for objective reasons, diet cannot cover requirements or when a deficiency has already developed. Examples: vitamin B12 for vegans, vitamin D for low sun exposure, folate and iodine for women planning a pregnancy, and iron for confirmed iron deficiency anemia. In these cases, the dosage and duration of treatment are determined by a physician based on test results. [39]

A dangerous mistake is taking "shock" doses of fat-soluble vitamins A and D, as well as iron and vitamin B6, without proper guidance or supervision. Upper tolerable levels (ULs) have been established for these nutrients, sometimes slightly exceeding the daily requirements. Regularly exceeding these levels can lead to damage to the liver, kidneys, nervous system, and bones. [40]

A reasonable algorithm looks like this: an assessment of diet and risk factors, laboratory diagnostics for key deficiencies if necessary, then targeted nutritional adjustments and the selection of supplements in physiological or slightly increased doses, with subsequent monitoring. This approach allows vitamins to be used as a tool for prevention and treatment, rather than as a "lottery" with unpredictable results. [41]

Brief conclusion

Vitamin deficiency is a silent but powerful risk factor: it worsens health today and quietly increases the likelihood of serious illnesses in the future. Mindful eating, attention to risk groups, and the judicious use of fortified foods and supplements under the supervision of a specialist can prevent most of these problems and maintain health for years to come.