Conv. Plasma
Nigella Sativa
Peg.. Lambda

All vitamin A studies
Meta analysis
Home COVID-19 treatment researchVitamin AVitamin A (more..)
Melatonin Meta
Bromhexine Meta Metformin Meta
Budesonide Meta
Cannabidiol Meta Molnupiravir Meta
Colchicine Meta
Conv. Plasma Meta
Curcumin Meta Nigella Sativa Meta
Ensovibep Meta Nitazoxanide Meta
Famotidine Meta Paxlovid Meta
Favipiravir Meta Peg.. Lambda Meta
Fluvoxamine Meta Quercetin Meta
Hydroxychlor.. Meta Remdesivir Meta
Ivermectin Meta
Lactoferrin Meta

All Studies   Meta Analysis   Recent:  
0 0.5 1 1.5 2+ BTT improvement 75% Improvement Relative Risk Anosmia 68% Severe microsmia 70% Moderate microsmia 75% Vitamin A  Chung et al.  LATE TREATMENT  RCT  LONG COVID Does vitamin A reduce the risk of Long COVID (PASC)? RCT 24 patients in China (August 2020 - June 2021) Lower PASC with vitamin A (p=0.048) Chung et al., Brain Sciences, June 2023 Favors vitamin A Favors control

A Pilot Study of Short-Course Oral Vitamin A and Aerosolised Diffuser Olfactory Training for the Treatment of Smell Loss in Long COVID

Chung et al., Brain Sciences, doi:10.3390/brainsci13071014, NCT04900415
Jun 2023  
  Source   PDF   All Studies   Meta AnalysisMeta
RCT 24 patients with olfactory dysfunction post-COVID-19 in Hong Kong, showing significantly improved recovery with the addition of vitamin A to aerosolised diffuser olfactory training. 25,000IU vitamin A for 14 days.
relative BTT improvement, 75.1% better, RR 0.25, p = 0.048, treatment mean 3.01 (±2.52) n=9, control mean 0.75 (±1.67) n=8, vitamin A + OT vs. OT.
anosmia, 68.0% lower, RR 0.32, p = 0.47, treatment 0 of 9 (0.0%), control 1 of 8 (12.5%), NNT 8.0, relative risk is not 0 because of continuity correction due to zero events (with reciprocal of the contrasting arm), vitamin A + OT vs. OT.
severe microsmia, 70.4% lower, RR 0.30, p = 0.29, treatment 1 of 9 (11.1%), control 3 of 8 (37.5%), NNT 3.8, vitamin A + OT vs. OT.
moderate microsmia, 74.6% lower, RR 0.25, p = 0.02, treatment 2 of 9 (22.2%), control 7 of 8 (87.5%), NNT 1.5, vitamin A + OT vs. OT.
Effect extraction follows pre-specified rules prioritizing more serious outcomes. Submit updates
Chung et al., 30 Jun 2023, Randomized Controlled Trial, China, peer-reviewed, 14 authors, study period 14 August, 2020 - 11 June, 2021, trial NCT04900415 (history).
Contact: (corresponding author),,
All Studies   Meta Analysis   Submit Updates or Corrections
This PaperVitamin AAll
A Pilot Study of Short-Course Oral Vitamin A and Aerosolised Diffuser Olfactory Training for the Treatment of Smell Loss in Long COVID
Tom Wai-Hin Chung, Hui Zhang, Fergus Kai-Chuen Wong, Siddharth Sridhar, Tatia Mei-Chun Lee, Gilberto Ka-Kit Leung, Koon-Ho Chan, Kui-Kai Lau, Anthony Raymond Tam, Deborah Tip-Yin Ho, Vincent Chi-Chung Cheng, Kwok-Yung Yuen, Ivan Fan-Ngai Hung, Henry Ka-Fung Mak
Brain Sciences, doi:10.3390/brainsci13071014
Background: Olfactory dysfunction (OD) is a common neurosensory manifestation in long COVID. An effective and safe treatment against COVID-19-related OD is needed. Methods: This pilot trial recruited long COVID patients with persistent OD. Participants were randomly assigned to receive short-course (14 days) oral vitamin A (VitA; 25,000 IU per day) and aerosolised diffuser olfactory training (OT) thrice daily (combination), OT alone (standard care), or observation (control) for 4 weeks. The primary outcome was differences in olfactory function by butanol threshold tests (BTT) between baseline and end-of-treatment. Secondary outcomes included smell identification tests (SIT), structural MRI brain, and serial seed-based functional connectivity (FC) analyses in the olfactory cortical network by resting-state functional MRI (rs-fMRI). Results: A total of 24 participants were randomly assigned to receive either combination treatment (n = 10), standard care (n = 9), or control (n = 5). Median OD duration was 157 days (IQR 127-175). Mean baseline BTT score was 2.3 (SD 1.1). At end-of-treatment, mean BTT scores were significantly higher for the combination group than control (p < 0.001, MD = 4.4, 95% CI 1.7 to 7.2) and standard care (p = 0.009) groups. Interval SIT scores increased significantly (p = 0.009) in the combination group. rs-fMRI showed significantly higher FC in the combination group when compared to other groups. At end-of-treatment, positive correlations were found in the increased FC at left inferior frontal gyrus and clinically significant improvements in measured BTT (r = 0.858, p < 0.001) and SIT (r = 0.548, p = 0.042) scores for the combination group. Conclusions: Short-course oral VitA and aerosolised diffuser OT was effective as a combination treatment for persistent OD in long COVID.
Abdelalim, Mohamady, Elsayed, Elawady, Ghallab, Corticosteroid nasal spray for recovery of smell sensation in COVID-19 patients: A randomized controlled trial, Am. J. Otolaryngol. 2021, doi:10.1016/j.amjoto.2020.102884
Addison, Wong, Ahmed, Macchi, Konstantinidis et al., Clinical Olfactory Working Group consensus statement on the treatment of postinfectious olfactory dysfunction, J. Allergy Clin. Immunol, doi:10.1016/j.jaci.2020.12.641
Al Aïn, Poupon, Hétu, Mercier, Steffener et al., Smell training improves olfactory function and alters brain structure, Neuroimage, doi:10.1016/j.neuroimage.2019.01.008
Ashburner, A fast diffeomorphic image registration algorithm, Neuroimage, doi:10.1016/j.neuroimage.2007.07.007
Brann, Tsukahara, Weinreb, Lipovsek, Van Den Berge et al., Non-neuronal expression of SARS-CoV-2 entry genes in the olfactory system suggests mechanisms underlying COVID-19-associated anosmia, doi:10.1126/sciadv.abc5801
Bryche, St Albin, Murri, Lacôte, Pulido et al., Massive transient damage of the olfactory epithelium associated with infection of sustentacular cells by SARS-CoV-2 in golden Syrian hamsters, Brain Behav. Immun, doi:10.1016/j.bbi.2020.06.032
Cain, Gent, Goodspeed, Leonard, Evaluation of olfactory dysfunction in the Connecticut Chemosensory Clinical Research Center, Laryngoscope, doi:10.1288/00005537-198801000-00017
Chan, -W.; Yuan, Kok, To, Chu et al., A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: A study of a family cluster, Lancet, doi:10.1016/S0140-6736(20)30154-9
Chu, Chan, Yuen, Shuai, Yuan et al., Comparative tropism, replication kinetics, and cell damage profiling of SARS-CoV-2 and SARS-CoV with implications for clinical manifestations, transmissibility, and laboratory studies of COVID-19: An observational study, Lancet Microbe, doi:10.1016/S2666-5247(20)30004-5
Chung, Sridhar, Zhang, Chan, Li et al., Olfactory Dysfunction in Coronavirus Disease 2019 Patients: Observational Cohort Study and Systematic Review, Open. Forum Infect. Dis, doi:10.1093/ofid/ofaa199
Chung, Zhang, Wong, Sridhar, Chan et al., Neurosensory Rehabilitation and Olfactory Network Recovery in Covid-19-related Olfactory Dysfunction, Brain Sci
Damm, Pikart, Reimann, Burkert, Göktas et al., Olfactory training is helpful in postinfectious olfactory loss: A randomized, controlled, multicenter study, Laryngoscope, doi:10.1002/lary.24340
Davis, Assaf, Mccorkell, Wei, Low et al., Characterizing long COVID in an international cohort: 7 months of symptoms and their impact, EClinicalMedicine, doi:10.1016/j.eclinm.2021.101019
Doty, Shaman, Dann, Development of the University of Pennsylvania Smell Identification Test: A standardized microencapsulated test of olfactory function, Physiol. Behav, doi:10.1016/0031-9384(84)90269-5
Duncan, Briggs, Treatment of Uncomplicated Anosmia by Vitamin A, Arch. Otolaryngol, doi:10.1001/archotol.1962.00740040122008
Ercoli, Masala, Pinna, Orofino, Solla et al., Qualitative smell/taste disorders as sequelae of acute COVID-19, Neurol. Sci. 2021, doi:10.1007/s10072-021-05611-6
Everett, Lean, Byrne, Van Diemen, Rhodes et al., Intranasal Infection of Ferrets with SARS-CoV-2 as a Model for Asymptomatic Human Infection
Fjaeldstad, Fernandes, Van Hartevelt, Gleesborg, Møller et al., Brain fingerprints of olfaction: A novel structural method for assessing olfactory cortical networks in health and disease, Sci. Rep
Guan, Ni, Hu, Liang, Ou et al., Clinical Characteristics of coronavirus disease 2019 in China, N. Engl. J. Med, doi:10.1056/NEJMoa2002032
Herrick, Lin, Peterson, Schnittke, Schwob, Notch1 maintains dormancy of olfactory horizontal basal cells, a reserve neural stem cell, Proc. Natl. Acad. Sci, doi:10.1073/pnas.1701333114
Hopkins, Alanin, Philpott, Harries, Whitcroft et al., Management of new onset loss of sense of smell during the COVID-19 pandemic-BRS Consensus Guidelines, Clin. Otolaryngol, doi:10.1111/coa.13636
Huang, Huang, Wang, Li, Ren et al., 6-month consequences of COVID-19 in patients discharged from hospital: A cohort study, Lancet, doi:10.1016/S0140-6736(20)32656-8
Huiming, Chaomin, Meng, Vitamin A for treating measles in children, Cochrane Database Syst Rev
Hummel, Whitcroft, Rueter, Haehner, Intranasal vitamin A is beneficial in post-infectious olfactory loss, Eur. Arch. Otorhinolaryngol, doi:10.1007/s00405-017-4576-x
Hussey, Klein, Randomized, Controlled Trial of Vitamin A in Children with Severe Measles, N. Engl. J. Med, doi:10.1056/NEJM199007193230304
Jiao, Yang, Yu, Zhao, Long et al., The olfactory route is a potential way for SARS-CoV-2 to invade the central nervous system of rhesus monkeys, Signal. Transduct. Target, doi:10.1038/s41392-021-00591-7
Karnath, New insights into the functions of the superior temporal cortex, Nat. Rev. Neurosci, doi:10.1038/35086057
Kartal, Yaşar, Kartal, Özcan, Borlu, Effects of isotretinoin on the olfactory function in patients with acne, Bras. Derm, doi:10.1590/abd1806-4841.20175483
Karunanayaka, Wilson, Tobia, Martinez, Meadowcroft et al., Default mode network deactivation during odor-visual association, Brain Mapp, doi:10.1002/hbm.23440
Kasiri, Rouhani, Salehifar, Ghazaeian, Fallah, Mometasone furoate nasal spray in the treatment of patients with COVID-19 olfactory dysfunction: A randomized, double blind clinical trial, Int. Immunopharmacol, doi:10.1016/j.intimp.2021.107871
Kirschenbaum, Imbach, Ulrich, Rushing, Keller et al., Inflammatory olfactory neuropathy in two patients with COVID-19, Lancet, doi:10.1016/S0140-6736(20)31525-7
Kollndorfer, Fischmeister, Kowalczyk, Hoche, Mueller et al., Olfactory training induces changes in regional functional connectivity in patients with long-term smell loss, NeuroImage Clin, doi:10.1016/j.nicl.2015.09.004
Kollndorfer, Kowalczyk, Hoche, Mueller, Pollak et al., Recovery of Olfactory Function Induces Neuroplasticity Effects in Patients with Smell Loss, Neural Plast, doi:10.1155/2014/140419
Langdon, Lehrer, Berenguer, Laxe, Alobid et al., Olfactory Training in Post-Traumatic Smell Impairment: Mild Improvement in Threshold Performances: Results from a Randomized Controlled Trial, J. Neurotrauma, doi:10.1089/neu.2017.5230
Leung, Coulombe, Reed, Contribution of olfactory neural stem cells to tissue maintenance and regeneration, Nat. Neurosci, doi:10.1038/nn1882
Lu, Yang, Zhang, Eslinger, Zhang et al., Disruptions of the olfactory and default mode networks in Alzheimer's disease, Brain Behav, doi:10.1002/brb3.1296
Margulies, Kelly, Uddin, Biswal, Castellanos et al., Mapping the functional connectivity of anterior cingulate cortex, Neuroimage, doi:10.1016/j.neuroimage.2007.05.019
Matschke, Lütgehetmann, Hagel, Sperhake, Schröder et al., Neuropathology of patients with COVID-19 in Germany: A post-mortem case series, Lancet Neurol, doi:10.1016/S1474-4422(20)30308-2
Meinhardt, Radke, Dittmayer, Franz, Thomas et al., Olfactory transmucosal SARS-CoV-2 invasion as a port of central nervous system entry in individuals with COVID-19, Nat. Neurosci, doi:10.1038/s41593-020-00758-5
Menni, Valdes, Polidori, Antonelli, Penamakuri et al., Symptom prevalence, duration, and risk of hospital admission in individuals infected with SARS-CoV-2 during periods of omicron and delta variant dominance: A prospective observational study from the ZOE COVID Study, Lancet, doi:10.1016/S0140-6736(22)00327-0
Moffett, Ross, Arun, Madhavarao, Namboodiri, N-Acetylaspartate in the CNS: From neurodiagnostics to neurobiology, Prog. Neurobiol, doi:10.1016/j.pneurobio.2006.12.003
Oz, Alger, Barker, Bartha, Bizzi et al., Clinical proton MR spectroscopy in central nervous system disorders, Radiology, doi:10.1148/radiol.13130531
Paschaki, Cammas, Muta, Matsuoka, Mak et al., Retinoic acid regulates olfactory progenitor cell fate and differentiation, Neural Dev, doi:10.1186/1749-8104-8-13
Peterson, Lin, Barrios-Camacho, Herrick, Holbrook et al., Activating a Reserve Neural Stem Cell Population In Vitro Enables Engraftment and Multipotency after Transplantation, Stem Cell. Rep, doi:10.1016/j.stemcr.2019.02.014
Psaltis, Li, Vaezeafshar, Cho, Hwang, Modification of the lund-kennedy endoscopic scoring system improves its reliability and correlation with patient-reported outcome measures, Laryngoscope, doi:10.1002/lary.24654
Rashid, Zgair, Al-Ani, Effect of nasal corticosteroid in the treatment of anosmia due to COVID-19: A randomised double-blind placebo-controlled study, Am. J. Otolaryngol. 2021, doi:10.1016/j.amjoto.2021.103033
Reden, Lill, Zahnert, Haehner, Hummel, Olfactory function in patients with postinfectious and posttraumatic smell disorders before and after treatment with vitamin A: A double-blind, placebo-controlled, randomized clinical trial, Laryngoscope, doi:10.1002/lary.23405
Reichert, Schöpf, Olfactory Loss and Regain: Lessons for Neuroplasticity, doi:10.1177/1073858417703910
Royet, Koenig, Gregoire, Cinotti, Lavenne et al., Functional anatomy of perceptual and semantic processing for odors, J. Cogn. Neurosci, doi:10.1162/089892999563166
Savic, Berglund, Passive perception of odors and semantic circuits, Hum. Brain Mapp, doi:10.1002/hbm.20009
Schurink, Roos, Radonic, Barbe, Bouman et al., Viral presence and immunopathology in patients with lethal COVID-19: A prospective autopsy cohort study, Lancet Microbe, doi:10.1016/S2666-5247(20)30144-0
Shearer, Stoney, Morgan, Mccaffery, A vitamin for the brain, Trends Neurosci, doi:10.1016/j.tins.2012.08.005
Sudre, Murray, Varsavsky, Graham, Penfold et al., Attributes and predictors of long COVID, Nat. Med, doi:10.1038/s41591-021-01292-y
To, Sridhar, Chiu, Hung, Li et al., Lessons learned 1 year after SARS-CoV-2 emergence leading to COVID-19 pandemic, Emerg. Microbes Infect, doi:10.1080/22221751.2021.1898291
Tyler, Marslen-Wilson, Randall, Wright, Devereux et al., Left inferior frontal cortex and syntax: Function, structure and behaviour in patients with left hemisphere damage, Brain, doi:10.1093/brain/awq369
Tzourio-Mazoyer, Landeau, Papathanassiou, Crivello, Etard et al., Automated anatomical labeling of activations in SPM using a macroscopic anatomical parcellation of the MNI MRI single-subject brain, Neuroimage, doi:10.1006/nimg.2001.0978
Vaira, Hopkins, Petrocelli, Lechien, Cutrupi et al., Efficacy of corticosteroid therapy in the treatment of long-lasting olfactory disorders in COVID-19 patients, Rhinology, doi:10.4193/Rhin20.515
Vihta, Pouwels, Peto, Pritchard, House et al., Omicron-associated changes in SARS-CoV-2 symptoms in the United Kingdom, Clin. Infect. Dis
Yildiz, Koca Yildiz, Kuzu, Günebakan, Bucak et al., Comparison of the Healing Effect of Nasal Saline Irrigation with Triamcinolone Acetonide Versus Nasal Saline Irrigation alone in COVID-19 Related Olfactory Dysfunction: A Randomized Controlled Study, Indian J. Otolaryngol. Head Neck Surg, doi:10.1007/s12070-021-02749-9
Yousem, Geckle, Bilker, Mckeown, Doty, Posttraumatic olfactory dysfunction: MR and clinical evaluation, AJNR Am. J. Neuroradiol
Zahn, Moll, Krueger, Huey, Garrido et al., Social concepts are represented in the superior anterior temporal cortex, Proc. Natl. Acad. Sci, doi:10.1073/pnas.0607061104
Zhang, Chu, Han, Shuai, Deng et al., SARS-CoV-2 infects human neural progenitor cells and brain organoids, Cell. Res, doi:10.1038/s41422-020-0390-x
Zhang, Chung, Wong, Hung, Mak et al., Changes in the Intranetwork and Internetwork Connectivity of the Default Mode Network and Olfactory Network in Patients with COVID-19 and Olfactory Dysfunction, Brain Sci, doi:10.3390/brainsci12040511
Zhang, Hao, Manor, Novak, Milberg et al., Intranasal insulin enhanced resting-state functional connectivity of hippocampal regions in type 2 diabetes, Diabetes, doi:10.2337/db14-1000
Zhang, Lee, Chu, Chan, Fan et al., Severe Acute Respiratory Syndrome Coronavirus 2 Infects and Damages the Mature and Immature Olfactory Sensory Neurons of Hamsters, Clin. Infect. Dis, doi:10.1093/cid/ciaa995
Zheng, Wong, Li, Verma, Ortiz et al., COVID-19 treatments and pathogenesis including anosmia in K18-hACE2 mice, Nature
Late treatment
is less effective
Please send us corrections, updates, or comments. Vaccines and treatments are complementary. All practical, effective, and safe means should be used based on risk/benefit analysis. No treatment, vaccine, or intervention is 100% available and effective for all current and future variants. We do not provide medical advice. Before taking any medication, consult a qualified physician who can provide personalized advice and details of risks and benefits based on your medical history and situation. FLCCC and WCH provide treatment protocols.
  or use drag and drop