VITAMIN D DEFICIENCY: CAUSES, THE ROLE OF PROCESSED FOODS, AND EVIDENCE-BASED SOLUTION STRATEGIES

Vitamin D is not merely a vitamin in the classical sense; it functions as a hormone-like compound that regulates numerous physiological processes. Its most recognized role is maintaining calcium and phosphorus homeostasis, which is essential for bone mineralization and skeletal integrity. However, scientific research over the past two decades has clearly demonstrated that vitamin D’s influence extends far beyond bone health.

Vitamin D receptors (VDRs) are expressed in a wide variety of tissues, including immune cells, brain tissue, cardiac muscle, pancreatic cells, and vascular endothelium. This widespread distribution explains why vitamin D affects immune regulation, inflammation control, muscle function, neuromuscular coordination, and endocrine balance.

Inadequate vitamin D levels have been associated with increased susceptibility to infections, muscle weakness, chronic fatigue, and an elevated risk of autoimmune and cardiovascular diseases. Deficiency does not simply result in osteoporosis or osteomalacia; it contributes to a systemic vulnerability affecting multiple organ systems.

From a public health perspective, vitamin D deficiency represents a silent but profound threat that compromises long-term health outcomes across populations.

The global rise in vitamin D deficiency is largely a consequence of modern living conditions that conflict with human evolutionary biology. Humans evolved with regular exposure to sunlight, which is essential for endogenous vitamin D synthesis. Today, however, people spend most of their time indoors, work in enclosed environments, and often avoid sunlight.

Urbanization, air pollution, and high-rise buildings further reduce effective ultraviolet B (UVB) exposure. Seasonal variation also limits vitamin D synthesis during autumn and winter, particularly in higher latitudes.

Dietary patterns have shifted dramatically as traditional diets rich in fatty fish, eggs, and natural dairy products have been replaced by highly processed, nutrient-poor foods. This transition has contributed to “hidden hunger,” where micronutrient deficiencies occur despite adequate or excessive caloric intake.

Vitamin D deficiency is therefore not an isolated issue but a reflection of systemic lifestyle and dietary changes.

Processed and ultra-processed foods undergo extensive industrial treatments designed to enhance shelf life, taste, and convenience. These processes often strip foods of natural micronutrients, including fat-soluble vitamins such as vitamin D. Heat treatment and refining can significantly reduce vitamin D content.

More importantly, high consumption of processed foods displaces natural vitamin D sources from the diet. When meals consist primarily of packaged snacks, refined carbohydrates, sugary beverages, and industrial fats, the intake of vitamin D-rich foods—such as fatty fish and eggs—declines sharply.

Emerging evidence also suggests that certain additives, trans fats, and high-fructose sweeteners may indirectly impair vitamin D metabolism. Observational studies have shown an inverse relationship between ultra-processed food consumption and serum 25-hydroxyvitamin D levels.

Thus, vitamin D deficiency is not only a result of insufficient sunlight but also a consequence of industrialized dietary patterns.

Vitamin D deficiency often develops insidiously, with symptoms that are nonspecific and easily mistaken for other conditions. Common complaints include diffuse bone pain—particularly in the lower back and hips—muscle weakness, cramps, and persistent fatigue.

Because vitamin D supports immune function, frequent infections, prolonged recovery, and increased susceptibility to respiratory illnesses may occur. Psychological symptoms such as low mood, depressive features, and cognitive difficulties have also been associated with low vitamin D levels.

In severe or prolonged deficiency, bone mineral density declines, increasing the risks of osteomalacia, osteoporosis, falls, and fractures—especially in older adults.

Because these findings lack specificity, laboratory measurement of serum 25-hydroxyvitamin D is essential for accurate diagnosis.

Vitamin D is a key immunomodulator that influences both innate and adaptive immune responses. It enhances the production of antimicrobial peptides that support the body’s first line of defense against pathogens.

When vitamin D levels are insufficient, immune responses become dysregulated, increasing susceptibility to respiratory infections and potentially worsening disease severity.

Vitamin D also helps regulate inflammation, limiting excessive immune activation that can damage tissues. By supporting immune tolerance, it may reduce autoimmune tendencies.

From an immunological standpoint, deficiency represents a state of compromised defense and heightened inflammatory risk.

High-risk groups include individuals with limited sun exposure, older adults, people with darker skin pigmentation, individuals with obesity, and those consuming predominantly processed foods.

Malabsorption disorders, gastrointestinal surgery, and long-term use of certain medications may also increase risk. Pregnant and breastfeeding women have higher requirements and are therefore more vulnerable.

Regular monitoring and, when appropriate, supplementation are important in these groups.

Sunlight is the most natural source of vitamin D, but it is often insufficient in modern lifestyles. Season, latitude, skin pigmentation, age, and sunscreen use can substantially limit vitamin D synthesis.

In many settings—especially during winter months—sun exposure alone cannot maintain optimal serum vitamin D levels year-round.

Dietary sources of vitamin D are limited. Fatty fish, egg yolks, and liver contain meaningful amounts, but they are not consumed regularly by many individuals.

Therefore, dietary intake alone often fails to meet physiological requirements.

Vitamin D supplementation is recommended for individuals with documented low blood levels. People with limited sun exposure, indoor lifestyles, darker skin pigmentation, or inadequate dietary intake are at higher risk.

Obesity, malabsorption disorders, and certain chronic conditions also predispose individuals to deficiency. In these cases, supplementation supports bone health and immune function.

Both the need for supplementation and the appropriate dose should be individualized and guided by laboratory measurements.

Yes. Excessive vitamin D intake can lead to serious health problems. As a fat-soluble vitamin, it accumulates in the body, and uncontrolled high-dose supplementation may result in hypercalcemia.

Hypercalcemia can cause kidney stones, impaired renal function, cardiac rhythm disturbances, nausea, and muscle weakness—especially with long-term high-dose use.

Vitamin D should not be treated as a harmless supplement; safe supplementation requires appropriate dosing and regular blood monitoring.

Vitamin D increases intestinal calcium absorption and supports bone health. However, high vitamin D intake without proper regulation may increase the risk of calcium deposition in soft tissues, including blood vessels.

Vitamin K2 activates proteins that direct calcium toward bones and away from vascular tissue, helping reduce the risk of vascular calcification.

This combination is often considered a safer, more balanced approach for individuals using vitamin D supplements long-term.

Vitamin D deficiency in childhood is a major public health concern because it directly affects skeletal development. Insufficient vitamin D can lead to rickets, bone deformities, growth retardation, and muscle weakness.

Vitamin D also supports immune function, and deficiency may increase susceptibility to infections. Adequate vitamin D in early life is essential for healthy bone development and long-term skeletal strength.

Therefore, routine vitamin D supplementation in children is widely considered a cornerstone of preventive healthcare.

With age, the skin’s capacity to synthesize vitamin D declines. Intestinal absorption may decrease, and the kidneys’ ability to convert vitamin D into its active form can weaken.

Older adults often spend less time outdoors and may have reduced dietary diversity, contributing to higher deficiency rates.

This deficiency is associated with osteoporosis, falls, and muscle weakness; regular screening and appropriate supplementation are particularly important in this group.

Vitamin D deficiency is diagnosed by measuring serum 25-hydroxyvitamin D. Symptoms such as fatigue, muscle pain, or bone tenderness may occur but are not sufficient for diagnosis because they overlap with many other conditions.

Laboratory testing provides an objective assessment of deficiency severity and guides safe treatment planning.

Regular blood testing is therefore considered the most accurate method, especially for individuals at increased risk.

Prevention requires a comprehensive and sustainable approach. Balanced nutrition that prioritizes nutrient-dense whole foods and reduces processed food intake is foundational.

Regular, controlled sun exposure supports endogenous vitamin D synthesis. For high-risk groups—such as children, older adults, and individuals with chronic conditions—appropriate-dose supplementation may be needed.

This strategy protects bone and immune health and reduces deficiency-related complications at the population level.