ANSWER

Ageing, nutrition and health status are the important factors affecting immune competence and cognitive performance¹⁷. The aging immune system loses the ability to protect against infections and cancer while declined cognitive function may eventually result in neurodegenerative diseases^9,33.

Vitamins are micronutrients which are essential for the maintenance of immune system and plays crucial role over the long run in supporting brain health. Here’s a summary of what science has found.

Vitamins	Description
Vitamin A	Vitamin A deficiency increases the risk of infectious diseases due to the inappropriate immune cell trafficking and functions11. Essential for the development of the central nervous system, protects and assists rejuvenation of the neuronal cells18,21.
Vitamin B1 (Thiamine)	Able to improve immune system function and reduce the risk of mental disorders and neurodegenerative disorders11,19. Adequate thiamine levels are likely to aid in the proper immune responses during COVID-19 infection27. Coenzyme necessary in synthesis of neurotransmitters and bioactive compounds essential for brain function13.
Vitamin B2 (Riboflavin)	Activates phagocytic activity and stimulates the multiplication of white blood cells29. Incidence of cognitive impairment of elderly men that had a high dietary intake of riboflavin (≥1.11 mg/day) was significantly lower compared to those had a low dietary intake of riboflavin (≤0.96 mg/day)1.
Vitamin B3 (Niacin)	Has anti-inflammatory properties by modulating host immune cells and maintenance of immunological homeostasis34. Important precursor to cofactors for brain functions, including neurotransmission, learning, memory7 and suppresses oxidative stress32,35.
Vitamin B5 (Pantothetic Acid)	Regulates immune response to resist infection and trigger epithelial cells to express inflammatory cytokines8. Substrate for synthesis of coenzyme A (CoA) which contributes to synthesis of neurotransmitters and structure of brain cells12. Neurodegeneration/dementia might be preventable by treatment with vitamin B522.
Vitamin B6 (Pyridoxine)	Help in regulates inflammation by acting in pathways that produce metabolites with immunomodulatory effects31. Required for the synthesis of the neurotransmitters in the brain28.
Vitamin B8 (Biotin)	Regulates immunological and inflammatory functions such as maturation and responsiveness of immune cells24. 300mg biotin daily improved multiple sclerosis-related disability in an open-label study26.
Vitamin B9 (Folic Acid)	Vitamin B9 deficiency inhibits the proliferation of killer T cells34. Maternal daily intake of folic acid of ≥600μg during first month of pregnancy was associated with reduced risk of autism spectrum disorder in children25. Daily oral administration of a 400-μg folic acid supplement to mild cognitive impairment (MCI) subjects for 12 months can significantly improve cognitive performance16.
Vitamin B12 (Cyanocobalamin)	Plays important role in cellular immunity, especially related to cytotoxic cells4. Low Vitamin B12 concentrations (<304 pmol/L) are associated with poorer memory performance in in patients with MCI14.
Vitamin C	Vitamin C supports epithelial barrier function against pathogens, enhance phagocytosis and microbial killing3. Supplementation with doses of 200 mg or more daily is effective in ameliorating the severity and duration of the common cold10. Cognitively intact subjects with adequate plasma vitamin C levels (≥28 μmol/L) demonstrated significantly better performance on cognitive assessments  as compared with those with deficient levels (<28 μmol/L)30.
Vitamin D	Vitamin D deficiency has been linked to various respiratory infections6. Has neuroprotective effects towards Alzheimer’s disease2. Many experts suggest that  ≥ 25-50μg of vitamin D daily is necessary for older people2.
Vitamin E	Modulates immune function by affects host susceptibility to infectious diseases15. Important antioxidant that protects brain cells from damage associated with oxidative stress5. High plasma levels of total vitamin E (≥ 8.81µmol per mmol cholesterol) were associated with better cognitive performance5.
Vitamin K	Cofactor for plasma proteins affecting immune and inflammatory responses particularly mediated by T cells20. An epidemiological study has reported a significant association between higher serum vitamin K1 concentration and better verbal episodic memory performance in older adults23.

 

References

¹Araki, A., Yoshimura, Y., Sakurai, T., Umegaki, H., Kamada, C., & Iimuro, S. et al. (2016). Low intakes of carotene, vitamin B2, pantothenate and calcium predict cognitive decline among elderly patients with diabetes mellitus: The Japanese Elderly Diabetes Intervention Trial. Geriatrics & Gerontology International, 17(8), 1168-1175. https://doi.org/10.1111/ggi.12843

²Boucher, B. J. (2012). The problems of vitamin d insufficiency in older people. Aging and disease, 3(4), 313–329.

³Carr, A., & Maggini, S. (2017). Vitamin C and Immune Function. Nutrients, 9(11), 1211. https://doi.org/10.3390/nu9111211

⁴Dehghani-Samani, A., Kamali, M., & Hoseinzadeh-Chahkandak, F. (2020). The Role of Vitamins on the Prevention and/or Treatment of COVID-19 Infection; a Systematic Review. Modern Care Journal, 17(3), e104740. https://doi.org/10.5812/modernc.104740

⁵Fata, G., Weber, P., & Mohajeri, M. (2014). Effects of Vitamin E on Cognitive Performance during Ageing and in Alzheimer’s Disease. Nutrients, 6(12), 5453-5472. https://doi.org/10.3390/nu6125453

⁶García de Tena, J., El Hachem Debek, A., Hernández Gutiérrez, C., & Izquierdo Alonso, J. (2014). Papel de la vitamina D en enfermedad pulmonar obstructiva crónica, asma y otras enfermedades respiratorias. Archivos De Bronconeumología, 50(5), 179-184. https://doi.org/10.1016/j.arbres.2013.11.023

⁷Gasperi, V., Sibilano, M., Savini, I., & Catani, M. (2019). Niacin in the Central Nervous System: An Update of Biological Aspects and Clinical Applications. International Journal Of Molecular Sciences, 20(4), 974. https://doi.org/10.3390/ijms20040974

⁸Gheita, A. A., Gheita, T. A., & Kenawy, S. A. (2019). The potential role of B5: A stitch in time and switch in cytokine. Phytotherapy Research, 34(2), 306-314. https://doi.org/10.1002/ptr.6537

⁹Gómez-Gómez, M., & Zapico, S. (2019). Frailty, Cognitive Decline, Neurodegenerative Diseases and Nutrition Interventions. International Journal Of Molecular Sciences, 20(11), 2842. https://doi.org/10.3390/ijms20112842

¹⁰Hemilä, H., & Chalker, E. (2013). Vitamin C for preventing and treating the common cold. The Cochrane database of systematic reviews, (1), CD000980. https://doi.org/10.1002/14651858.CD000980.pub4

¹¹Hosomi, K., & Kunisawa, J. (2017). The Specific Roles of Vitamins in the Regulation of Immunosurveillance and Maintenance of Immunologic Homeostasis in the Gut. Immune network, 17(1), 13–19. https://doi.org/10.4110/in.2017.17.1.13

¹²Kennedy, D. O. (2016). B Vitamins and the Brain: Mechanisms, Dose and Efficacy—A Review. Nutrients, 8(2), 68. https://doi.org/10.3390/nu8020068

¹³Kerns, J. C., Arundel, C., & Chawla, L. S. (2015). Thiamin Deficiency in People with Obesity. Advances In Nutrition, 6(2), 147-153. https://doi.org/10.3945/an.114.007526

¹⁴Köbe, T., Witte, A., Schnelle, A., Grittner, U., Tesky, V., & Pantel, J. et al. (2016). Vitamin B-12 concentration, memory performance, and hippocampal structure in patients with mild cognitive impairment. The American Journal Of Clinical Nutrition, 103(4), 1045-1054. https://doi.org/10.3945/ajcn.115.116970

¹⁵Lewis, E., Meydani, S., & Wu, D. (2018). Regulatory role of vitamin E in the immune system and inflammation. IUBMB Life, 71(4), 487-494. https://doi.org/10.1002/iub.1976

¹⁶Ma, F., Wu, T., Zhao, J., Song, A., Liu, H., Xu, W., & Huang, G. (2016). Folic acid supplementation improves cognitive function by reducing the levels of peripheral inflammatory cytokines in elderly Chinese subjects with MCI. Scientific Reports, 6(1). https://doi.org/10.1038/srep37486

¹⁷Maggini, S., Pierre, A., & Calder, P. (2018). Immune Function and Micronutrient Requirements Change over the Life Course. Nutrients, 10(10), 1531. https://doi.org/10.3390/nu10101531

¹⁸Mehta, V., Desai, N., Perwez, A., Nemade, D., Dawoodi, S., & Zaman, S. (2017). ACE Alzheimer’s: The Role of Vitamin A, C and E (ACE) in Oxidative Stress induced Alzheimer’s Disease. Journal Of Medical Research And Innovation, 2(1), e000086. https://doi.org/10.15419/jmri.86

¹⁹Mikkelsen, K., & Apostolopoulos, V. (2019). Vitamin B1, B2, B3, B5, and B6 and the Immune System. Nutrition And Immunity, 115-125. https://doi.org/10.1007/978-3-030-16073-9_7

²⁰Namazi, N., Larijani, B., & Azadbakht, L. (2019). Vitamin K and the Immune System. Nutrition And Immunity, 75-79. https://doi.org/10.1007/978-3-030-16073-9_4

²¹Ono, K., & Yamada, M. (2012). Vitamin A and Alzheimer’s disease. Geriatrics & gerontology international, 12(2), 180-188. https://doi.org/10.1111/j.1447-0594.2011.00786.x

²²Patassini, S., Begley, P., Xu, J., Church, S., Kureishy, N., & Reid, S. et al. (2019). Cerebral Vitamin B5 (D-Pantothenic Acid) Deficiency as a Potential Cause of Metabolic Perturbation and Neurodegeneration in Huntington’s Disease. Metabolites, 9(6), 113. https://doi.org/10.3390/metabo9060113

²³Presse, N., Belleville, S., Gaudreau, P., Greenwood, C., Kergoat, M., & Morais, J. et al. (2013). Vitamin K status and cognitive function in healthy older adults. Neurobiology Of Aging, 34(12), 2777-2783. https://doi.org/10.1016/j.neurobiolaging.2013.05.031

²⁴Saleem, F., & Soos, M. P. (2020). Biotin Deficiency. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK547751

²⁵Schmidt, R., Tancredi, D., Ozonoff, S., Hansen, R., Hartiala, J., & Allayee, H. et al. (2012). Maternal periconceptional folic acid intake and risk of autism spectrum disorders and developmental delay in the CHARGE (CHildhood Autism Risks from Genetics and Environment) case-control study. The American Journal Of Clinical Nutrition, 96(1), 80-89. https://doi.org/10.3945/ajcn.110.004416

²⁶Sedel, F., Bernard, D., Mock, D., & Tourbah, A. (2016). Targeting demyelination and virtual hypoxia with high-dose biotin as a treatment for progressive multiple sclerosis. Neuropharmacology, 110, 644-653. https://doi.org/10.1016/j.neuropharm.2015.08.028

²⁷Shakoor, H., Feehan, J., Mikkelsen, K., Al Dhaheri, A., Ali, H., & Platat, C. et al. (2021). Be well: A potential role for vitamin B in COVID-19. Maturitas, 144, 108-111. https://doi.org/10.1016/j.maturitas.2020.08.007

²⁸Stover, P., & Field, M. (2015). Vitamin B-6. Advances In Nutrition, 6(1), 132-133. https://doi.org/10.3945/an.113.005207

²⁹Suwannasom, N., Kao, I., Pruß, A., Georgieva, R., & Bäumler, H. (2020). Riboflavin: The Health Benefits of a Forgotten Natural Vitamin. International Journal Of Molecular Sciences, 21(3), 950. https://doi.org/10.3390/ijms21030950

³⁰Travica, N., Ried, K., Sali, A., Hudson, I., Scholey, A., & Pipingas, A. (2019). Plasma Vitamin C Concentrations and Cognitive Function: A Cross-Sectional Study. Frontiers In Aging Neuroscience, 11. https://doi.org/10.3389/fnagi.2019.00072

³¹Ueland, P., McCann, A., Midttun, Ø., & Ulvik, A. (2017). Inflammation, vitamin B6 and related pathways. Molecular Aspects Of Medicine, 53, 10-27. https://doi.org/10.1016/j.mam.2016.08.001

³²Wakade, C., Giri, B., Malik, A., Khodadadi, H., Morgan, J., Chong, R., & Baban, B. (2018). Niacin modulates macrophage polarization in Parkinson’s disease. Journal Of Neuroimmunology, 320, 76-79. https://doi.org/10.1016/j.jneuroim.2018.05.002

³³Weyand, C., & Goronzy, J. (2016). Aging of the Immune System. Mechanisms and Therapeutic Targets. Annals Of The American Thoracic Society, 13(Supplement_5), S422-S428. https://doi.org/10.1513/annalsats.201602-095aw

³⁴Yoshii, K., Hosomi, K., Sawane, K., & Kunisawa, J. (2019). Metabolism of Dietary and Microbial Vitamin B Family in the Regulation of Host Immunity. Frontiers In Nutrition, 6. https://doi.org/10.3389/fnut.2019.00048

³⁵Zhou, Y., Wu, J., Sheng, R., Li, M., Wang, Y., & Han, R. et al. (2018). Reduced Nicotinamide Adenine Dinucleotide Phosphate Inhibits MPTP-Induced Neuroinflammation and Neurotoxicity. Neuroscience, 391, 140-153. https://doi.org/10.1016/j.neuroscience.2018.08.032