What is the function of vitamins in the human body?

Functions of Vitamins in the Human Body

Core Metabolic and Cellular Functions

Vitamins serve as essential cofactors for enzymatic reactions, support cellular metabolism, and maintain normal physiological function across all organ systems. 1

Energy Metabolism and Biosynthesis

• B vitamins function as critical cofactors in both catabolic metabolism (energy production) and anabolic metabolism (biosynthesis of bioactive molecules), serving as essential components for cellular metabolic pathways 1
• B vitamins are cofactors for essential enzymes involved in RNA and DNA biosynthesis, making them fundamental to cellular replication and repair 1
• These water-soluble vitamins must be replaced daily since the body does not store them, requiring consistent dietary intake from animal proteins, dairy products, leafy green vegetables, and beans 1

Antioxidant Protection

• Vitamin E functions as the most important lipid-soluble antioxidant, protecting membrane lipids, lipoproteins, and depot fats from lipid peroxidation 2
• Vitamin E regulates production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that arise during metabolic processes and inflammation 2
• By preventing lipid peroxidation and associated membrane damage, vitamin E maintains the integrity and function of cell membranes, particularly critical for immune cells with high polyunsaturated fatty acid (PUFA) content 2

Immune System Regulation

Vitamin E and Immune Function

• Vitamin E inhibits protein kinase C (PKC) activity, resulting in decreased platelet aggregation, reduced proliferation of monocytes and macrophages, and decreased superoxide production in neutrophils 2
• Supplementation above recommended levels has demonstrated increased lymphocyte proliferation, enhanced delayed-type hypersensitivity response, increased IL-2 production, and decreased IL-6 production 2
• Immune cells are particularly enriched in vitamin E—monocytes contain 125-fold more vitamin E than erythrocytes, while neutrophils, lymphocytes, and platelets contain 23-fold, 20-fold, and 3-fold more, respectively 2

Vitamin D and Immune Modulation

• Vitamin D functions as a steroid hormone that enters cells via vitamin D receptors (VDR), complexes with retinoic acid X receptor, and binds DNA-responsive elements to regulate gene expression 2
• Vitamin D inhibits Th1 cell proliferation, the predominant T-helper cell type in autoimmune conditions like alopecia areata 2
• Vitamin D has established roles in preventing autoimmune disease, with studies showing 40% reduction in multiple sclerosis risk and reduced thyroid peroxidase antibody levels in autoimmune thyroid disease 2

Neurological and Cognitive Functions

Vitamin D and Brain Health

• Vitamin D affects multiple brain functions through both direct cerebral actions and indirect effects on other organ systems that influence neurocognition 2
• Critical periods exist where vitamin D has greatest CNS impact: prenatal period (neurological development), younger ages (cognitive reserve enhancement), and older ages (prevention of neurocognitive loss) 2
• Prenatal vitamin D deficiency causes profound brain alterations at birth, altered neuronal differentiation signals, and abnormal adult behaviors in animal models 2

B Vitamins and Neurological Function

• B vitamins serve as critical cofactors for axonal transport, neurotransmitter synthesis, and cellular metabolic pathways essential for nervous system function 1
• B vitamin deficiencies have been identified as etiological factors in various neurologic disorders and pathological states 1
• In aging populations, B vitamin deficiency links to cardiovascular disorders, cognitive dysfunction, osteoporosis, and methylation disorders 3

Bone and Musculoskeletal Health

Vitamin D and Calcium Homeostasis

• Vitamin D's primary role involves calcium and phosphorus homeostasis and bone health, maintained through UVB-mediated conversion of 7-dehydrocholesterol in skin to active 1,25-dihydroxyvitamin D 2
• Vitamin D has established roles in normal hair follicle function, with murine studies showing complete hair loss by 8 months in VDR knockout mice 2
• The vitamin D receptor (VDR) appears more causative than its ligand for hair follicle cycling, as wild-type mice with undetectable circulating 25(OH)D in UV-free environments did not develop alopecia 2

Cellular Turnover and Tissue Maintenance

Micronutrients in Rapidly Dividing Tissues

• The normal hair follicle cycle depends on micronutrients given their role in cellular turnover, a frequent occurrence in rapidly dividing hair follicles 2
• Micronutrients reduce oxidative stress, an increasingly suspected contributor to conditions like alopecia areata pathogenesis 2
• Vitamin D modifies immune response by inhibiting Th1 cell proliferation while supporting tissue regeneration 2

Critical Clinical Considerations

Population-Specific Vulnerabilities

• Subclinical vitamin D deficiency affects 41.6% of US adults with serum 25(OH)D levels below 20 ng/mL 2
• Geriatric populations face reduced food intake and absorption efficiency, warranting attention to dietary B vitamin levels 1
• Vitamin D deficiency in aging populations increases risk of developing cardiovascular disease, cognitive diseases, and osteoporosis 3

Ubiquitous Multi-System Effects

• Due to vitamin D's ubiquitous role, its effects extend beyond single organ systems—supplementation can simultaneously improve or deteriorate multiple conditions (e.g., improving hypertension while potentially causing vascular calcification) 2
• The balance between cognitive performance and other organ/tissue health related to neurocognition must be considered when evaluating vitamin supplementation effects 2