https://orcid.org/0000-0003-1053-4922
ABSTRACT
The aim of the present study is to compare the cognitive function and physical performance of young adults who have experienced the COVID-19 infection with those who have not. Twenty-one participants who had experienced the COVID-19 infection and 21 non-COVID controls underwent a cognitive assessment (Digit Span Forward Test: DSF, and Stroop Colour and Word Test: SCWT) and physical performance test (six-minute walk test: 6MWT). The participants in the COVID-19 group tended to have lower cognitive and physical performance than those in the control group. However, the difference was not statistically significant (DSF: p = 0.59, SCWT- Word: p = 0.18, SCWT- Color: p = 0.73, SCWT-Colour – Word t: p = 0.14, and 6MWT: p = 0.54). The cognitive function and physical performance in post-COVID-19 young adults tended to be lower than non-COVID-19 participants but failed to reach statistical significance. Further studies, particularly involving large sample sizes, are required to confirm the effect of COVID-19 in young adults.
Introduction
In January 2024, there were over 774 million confirmed cases of Coronavirus disease (COVID-19) worldwide (World Health Organization, Citation2024). Although the most common symptom of COVID-19 is pulmonary impairment, there is evidence to suggest that COVID-19 infection can affect many parts of the body, such as the cardiovascular system, nervous system, respiratory system, immune system, and gastrointestinal tract (Moslehi et al., Citation2022). Respiratory SARS-CoV-2 infection may induce elevated cytokine/chemokine levels, contributing to hippocampal microglial reactivity, impaired neurogenesis, and cognitive impairment (Fernández-Castañeda et al., Citation2022). The symptoms of post-COVID-19 cognitive impairment include impaired executive function, processing speed, memory, and attention (Becker et al., Citation2021; Henneghan et al., Citation2022). Such impairments may interfere with quality of life, occupation, as well as education. However, the prevalence of cognitive impairment after COVID-19 infection is unclear. A previous study found that cognitive impairment after the COVID-19 infection reached 81% (Jaywant et al., Citation2021), while another study reported that only 2.6% of patients had experienced cognitive decline (Monti et al., Citation2021). In addition, Rass et al. reported that 23% of COVID-19 patients had cognitive deficits. These included severe, moderate, and mild COVID-19 at 29%, 30%, and 3%, respectively (Rass et al., Citation2021). On the contrary, there has been evidence to support that no difference in cognitive performance was exhibited among participants who had a history of COVID-19 infection and those who did not (Saneemanomai, Citation2023).
A reduction in physical performance has also been reported in COVID-19 patients (Ahmed et al., Citation2022; Simonelli et al., Citation2021). The Barthel Index, 1-Min Sit-to-Stand, 6-Min Walking Test, and Short Physical Performance Battery were lower in COVID-19 patients when compared to the reference values (Simonelli et al., Citation2021).
Interestingly, previous studies have suggested physical performance to be associated with cognitive function (Dansereau et al., Citation2020; Handing et al., Citation2020). However, few studies have evaluated cognitive function and physical performance in mild COVID-19, particularly in young individuals. Additionally, since only a few studies have compared these outcomes between people with and without COVID-19, it is still unclear whether a reduction in physical and cognitive performance after COVID-19 is a direct negative effect of the infection or an indirect effect of the pandemic. To bridge this knowledge gap, the present study compares cognitive function and physical performance between young adults who experienced COVID-19 infection and those who had not. Cognitive dysfunction after mild COVID-19 May lead to reduced academic performance and quality of life in young adults. Early detection may be beneficial for planning treatment and reducing disease progression
Materials and methods
Participants
The sample size (n = 21/group) was calculated based on data from the previous study (Crivelli et al., Citation2022). The alpha level and power were set at 0.05 and 0.80, respectively. A total of 42 participants aged between 18 and 25 years were recruited through face-to-face contact and student societies. Of these, 21 had a history of a positive COVID-19 test result (COVID-19 group), while the other 21 did not (control group). Individuals were excluded if they had any pre-existing neurological, cardiopulmonary, and musculoskeletal disorders affecting their cognition and physical performance, visual and auditory impairment, and were not willing to participate in the study.
Procedure
This study was approved by the University of Phayao Ethics Committee, reference number UP-HEC 1.2/044/66. In the first part, all participants were interviewed about their age, education level, medical history, and experience of COVID-19. They were then asked to assess their anthropometry, cognitive function, and physical performance by the blind researchers, who were not involved in the interview process ().
Figure 1. Flow chart of study progress.
Measures
Cognitive function
Cognitive function was assessed by the Digit Span Forward Test (DSF) and Stroop Colour and Word Test (SCWT).
The DSF test was used to evaluate short-term memory, requiring participants to recall numbers in the same order as shown on a computer screen. The participants were asked to recall the numbers until they could not reproduce the correct number for two sequences of equal length (Nouchi et al., Citation2012). The length of the longest correctly repeated sequence was recorded (Orsini et al., Citation1987), with a higher score indicating better short-term memory.
The SCWT consists of three parts: 1) Word: participants were asked to read the name of colours (red, blue, and green) printed in black font; 2) Colour: participants were asked to name the ink colour (red, blue, and green) printed in XXX; and 3) Colour-Word: participants were required to name colours (red, blue, and green) printed in inconsistent coloured ink. For each condition, they were asked to read/name aloud as quickly as possible for 45 seconds, and the number of correct items was recorded. The Word and Colour condition reflects selective attention and processing speed, while the Colour-Word condition reflects executive function (Barella et al., Citation2010; Douris et al., Citation2018; Scarpina & Tagini, Citation2017). A higher score indicates a greater cognitive function.
Physical performance
Physical performance was assessed by the six-minute walk test (6MWT), performed in a 30-metre-long, flat, straight corridor. Participants rested in a sitting position for at least 10 minutes before starting the test. They were then asked to walk as far as possible in six minutes, and the distance walked was recorded. All participants were instructed not to have exercised vigorously for at least two hours before the test (Laboratories, Citation2002). A longer walking distance indicates a greater physical performance.
Statistical analysis
Descriptive statistics were used to describe the demographic variables. Normality was tested with the use of the Shapiro-Wilk test, and the main outcomes were compared using the independent t-test for parametric data or the Mann-Whitney U test for non-parametric. The Pearson correlation coefficient was used to evaluate the correlation between outcomes. A p-value of ≤ 0.05 was considered statistically significant. All data analysis was conducted with SPSS version 26.
Results
The participants in the COVID-19 group were 3–12 (7.84 ± 4.79) months post diagnosis of COVID-19. All were mild COVID-19 patients who recovered at home. Both the COVID-19 and control groups were health science students. The body mass index (BMI), waist circumference, and waist-to-hip ratio of the participants were mostly normal. In addition, there were no significant differences in baseline characteristics between the two groups ().
Table 1. Baseline characteristics.
The Digit Span Forward and Stroop Colour and Word test results for participants who had experienced the COVID-19 infection tended to be lower than those of the control group but failed to reach statistical significance. A similar trend was found in physical performance measured by 6MWT. Although the distance walked was less in the COVID-19 group, the difference did not reach statistical significance ().
Table 2. Cognitive function and physical performance.
Both the cognitive function and physical performance test results tended to be lower in the COVID-19 group, but no correlation between the two variables was found in the present study ().
Figure 2. Correlation between 6-minute walk test (6MWT) and digit span forward test (DSF).
Figure 3. Correlation between 6-minute walk test (6MWT) and Stroop color and word test (SCWT) color–word.
Discussion
The main finding of this study is that young adults who experienced COVID-19 tended to have lower cognitive and physical performance than those of the control participants. However, the difference did not reach statistical significance.
This finding was partially consistent with the previous study in that no statistically significant difference was revealed in cognitive function between patients who recovered from COVID-19 and those who had not experienced COVID-19 (Saneemanomai, Citation2023).
In addition, COVID-19 infection has been reported to have hardly any impact on cognitive function in the younger population (Francis & Thunell, Citation2023). On the contrary, Crivelli et al. reported that there were significant differences in memory, attention, executive function, and language between post-COVID-19 patients and healthy controls (Crivelli et al., Citation2022). Mild or moderate COVID-19 infection may be associated with cognitive impairment, especially executive function (Henneghan et al., Citation2022). The discrepancies between the present study and the previous studies may be explained by the risk factors for post-COVID cognitive dysfunction, such as older age and more acute COVID-19 severity (Quan et al., Citation2023; Sekendiz et al., Citation2023). The post-COVID-19 patients in the study of Crivelli were 50 years old with 31% of them being hospitalized. Additionally, the participants in the study of Henneghan were 36 years old, with 37% of them having moderate COVID-19 infection, whereas the participants in the present study were 20 years old, experienced mild COVID-19 infection, and recovered at home. The participants in the previous studies seemed to be at higher risk of post-COVID cognitive dysfunction. Therefore, the previous studies demonstrated that COVID-19 had a clearer effect on cognitive function.
The COVID-19 infection may have direct negative effects on the nervous system. The literature suggests that the potential mechanisms underlying neurological damage after COVID-19 infection were the SARS-CoV-2 virus invading the central nervous system via the olfactory mucosa (Altuna et al., Citation2021; Meinhardt et al., Citation2021), olfactory fibres, or haematogenous spread (Altuna et al., Citation2021; Meinhardt et al., Citation2021; Miners et al., Citation2020). The infected cells with SARS-CoV-2 May then cause mitochondrial dysfunction, leading to cell death or dysfunction (Wang et al., Citation2020). Further potential mechanisms such as neuroinflammation caused by an immune response to SARS-CoV-2 in the respiratory system, neuroinflammation and/or ischaemia of neurons by cerebrovascular disruption, and hypoxaemia had negative effects on neurons (Monje & Iwasaki, Citation2022).
The present study found that physical performance also tended to be lower in the COVID-19 group but failed to reach statistical significance. A previous study reported that the six-minute walking distance of healthy participants aged 20–50 years old was 593 and 638 metres for women and men, respectively (Chetta et al., Citation2006). The walking distance of the COVID-19 group in the present study was 581.76 ± 28.99 metres. It can, therefore, be seen that participants in the COVID-19 group seemed to have a shorter walking distance. This was partially supported by several studies that demonstrated a negative change in physical performance after COVID-19 infection (Ahmed et al., Citation2022; Simonelli et al., Citation2021). Systemic inflammation can cause impaired muscle protein metabolism, physical inactivity, and poor nutrition, contributing to muscle dysfunction leading to lower mobility, weakness, and impaired physical performance (Montes-Ibarra et al., Citation2022). In addition, cardiovascular dysfunction and impaired gas exchange may contribute to negative changes in physical performance after COVID-19. Moreover, reduced physical activity during quarantine caused by COVID-19 May result in a change in physical performance (Pelemiš et al., Citation2023)
The results of the present study did not show a clear negative effect of COVID-19 on cognitive function and physical performance. There are two possible explanations. Firstly, participants in this study were young adults who had only experienced mild symptoms. A previous study suggested that young individuals tended to recover faster from COVID-19 infection than older people (Voinsky et al., Citation2020). Secondly, a small sample size may have limited the statistical power to detect a difference (Leppink et al., Citation2016).
The present study has some limitations. Firstly, the sample size was small, although based on the sample size calculation. Further large-scale studies are required to confirm the effect of COVID-19 on young adults. Secondly, there was a lack of pre-COVID-19 assessment. It may be difficult to conclude the causal relationship between COVID-19 infection and reduced cognitive function and physical performance. However, the present study included the non-COVID-19 control group which may help to better understand the direct effect of COVID-19 in young adults. Thirdly, the results of the present study are based on the data from young adults with mild COVID-19, so these findings may have some limitations in explaining the effect of COVID-19 in another population group.
Conclusion
The results of this study demonstrated that cognitive function and physical performance in participants who recovered from COVID-19 tended to be lower than those control group, but the difference did not reach statistical significance. Further studies, particularly involving large sample sizes are required to confirm the effect of COVID-19 in young adults.
Acknowledgments
This study was supported by the Thailand Science Research and Innovation funds and the University of Phayao (Grant No. FF66-UoE009), and School of Allied Health Sciences, University of Phayao, Thailand.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
References
- Ahmed, R., Khan, S., Quddus, N., Saher, T., & Fatima, N. (2022). Physical performance among post-COVID and non-COVID individuals: A comparative study. Comparative Exercise Physiology, 18(4), 305–8. https://doi.org/10.3920/CEP220002
- Altuna, M., Sánchez-Saudinós, M. B., & Lleó, A. (2021). Cognitive symptoms after COVID-19. Neurology Perspectives, 1(24), 005. https://doi.org/10.1016/j.neurop.2021.10.005
- Barella, L. A., Etnier, J. L., & Chang, Y. K. (2010). The immediate and delayed effects of an acute bout of exercise on cognitive performance of healthy older adults. Journal of Aging and Physical Activity, 18(1), 87–98. https://doi.org/10.1123/japa.18.1.87
- Becker, J. H., Lin, J. J., Doernberg, M., Stone, K., Navis, A., Festa, J. R., & Wisnivesky, J. P. (2021). Assessment of cognitive function in patients after COVID-19 infection. JAMA Network Open, 4(10), e2130645–e2130645. https://doi.org/10.1001/jamanetworkopen.2021.30645
- Chetta, A., Zanini, A., Pisi, G., Aiello, M., Tzani, P., Neri, M., & Olivieri, D. (2006). Reference values for the 6-min walk test in healthy subjects 20-50 years old. Respiratory Medicine, 100(9), 1573–1578. https://doi.org/10.1016/j.rmed.2006.01.001
- Crivelli, L., Calandri, I., Corvalán, N., Carello, M. A., Keller, G., Martínez, C., Arruabarrena, M., & Allegri, R. (2022). Cognitive consequences of COVID-19: Results of a cohort study from South America. Arquivos de neuro-psiquiatria, 80(3), 240–247. https://doi.org/10.1590/0004-282x-anp-2021-0320
- Dansereau, A., Hunter, S. W., Gomez, F., Guralnik, J. M., DePaul, V. G., & Auais, M. (2020). Global cognition predicts the incidence of poor physical performance among older adults: A cross-national study. Geriatrics & Gerontology International, 20(3), 218–222. https://doi.org/10.1111/ggi.13864
- Douris, P. C., Handrakis, J. P., Apergis, D., Mangus, R. B., Patel, R., Limtao, J., Platonova, S., Gregorio, A., & Luty, E. (2018). The effects of aerobic exercise and gaming on cognitive performance. Journal of Human Kinetics, 61(1), 73–83. https://doi.org/10.1515/hukin-2017-0134
- Fernández-Castañeda, A., Lu, P., Geraghty, A. C., Song, E., Lee, M. H., Wood, J., O’Dea, M. R., Dutton, S., Shamardani, K., Nwangwu, K., Mancusi, R., Yalçın, B., Taylor, K. R., Acosta-Alvarez, L., Malacon, K., Keough, M. B., Ni, L., Woo, P. J. … Monje, M. (2022). Mild respiratory COVID can cause multi-lineage neural cell and myelin dysregulation. Cell, 185(14), 2452–2468.e2416. https://doi.org/10.1016/j.cell.2022.06.008
- Francis, G., & Thunell, E. (2023). COVID-19 infection does not seem to affect cognition in college students. Consciousness and Cognition, 108, 103464. https://doi.org/10.1016/j.concog.2023.103464
- Handing, E. P., Leng, X. I., Kritchevsky, S. B., & Craft, S. (2020). Association between physical performance and cognitive function in older adults across multiple studies: A pooled analysis study. Innovation in Aging, 4(6), igaa050. https://doi.org/10.1093/geroni/igaa050
- Henneghan, A. M., Lewis, K. A., Gill, E., & Kesler, S. R. (2022). Cognitive Impairment in Non-critical, Mild-to-Moderate COVID-19 Survivors. Frontiers in Psychology, 13, 770459. https://doi.org/10.3389/fpsyg.2022.770459
- Jaywant, A., Vanderlind, W. M., Alexopoulos, G. S., Fridman, C. B., Perlis, R. H., & Gunning, F. M. (2021). Frequency and profile of objective cognitive deficits in hospitalized patients recovering from COVID-19. Neuropsychopharmacology REVIEWS, 46(13), 2235–2240. https://doi.org/10.1038/s41386-021-00978-8
- Laboratories, A. T. S. C. O. P. S. F. C. P. F. (2002). ATS statement: Guidelines for the six-minute walk test. American Journal of Respiratory and Critical Care Medicine, 166(1), 111–117. https://doi.org/10.1164/ajrccm.166.1.at1102
- Leppink, J., Winston, K., & O’Sullivan, P. (2016). Statistical significance does not imply a real effect. Perspectives on Medical Education, 5(2), 122–124. https://doi.org/10.1007/s40037-016-0256-6
- Meinhardt, J., Radke, J., Dittmayer, C., Franz, J., Thomas, C., Mothes, R., Laue, M., Schneider, J., Brünink, S., Greuel, S., Lehmann, M., Hassan, O., Aschman, T., Schumann, E., Chua, R. L., Conrad, C., Eils, R., Stenzel, W. … Heppner, F. L. (2021). Olfactory transmucosal SARS-CoV-2 invasion as a port of central nervous system entry in individuals with COVID-19. Nature Neuroscience, 24(2), 168–175. https://doi.org/10.1038/s41593-020-00758-5
- Miners, S., Kehoe, P. G., & Love, S. (2020). Cognitive impact of COVID-19: Looking beyond the short term. Alzheimer’s Research & Therapy, 12(1), 170. https://doi.org/10.1186/s13195-020-00744-w
- Monje, M., & Iwasaki, A. (2022). The neurobiology of long COVID. Neuron, 110(21), 3484–3496. https://doi.org/10.1016/j.neuron.2022.10.006
- Montes-Ibarra, M., Oliveira, C. L. P., Orsso, C. E., Landi, F., Marzetti, E., & Prado, C. M. (2022). The impact of long COVID-19 on muscle health. Clinics in Geriatric Medicine, 38(3), 545–557. https://doi.org/10.1016/j.cger.2022.03.004
- Monti, G., Leggieri, C., Fominskiy, E., Scandroglio, A. M., Colombo, S., Tozzi, M., Moizo, E., Mucci, M., Crivellari, M., Pieri, M., Guzzo, F., Piemontese, S., De Lorenzo, R., Da Prat, V., Fedrizzi, M., Faustini, C., DiPiazza, M., Conte, F. … Zangrillo, A. (2021). Two-months quality of life of COVID-19 invasively ventilated survivors; an Italian single-center study. Acta Anaesthesiologica Scandinavica, 65(7), 912–920. https://doi.org/10.1111/aas.13812
- Moslehi, N., Jahromy, M. H., Ashrafi, P., Vatani, K., Nemati, M. A. H., Moghadam, P. A., Rostamian, F., & Jahromi, M. H. (2022). Multi-organ system involvement in coronavirus disease 2019 (COVID-19): A mega review. Journal of Family Medicine and Primary Care, 11(9), 5014–5023. https://doi.org/10.4103/jfmpc.jfmpc_1570_21
- Nouchi, R., Taki, Y., Takeuchi, H., Hashizume, H., Nozawa, T., Sekiguchi, A., Nouchi, H., & Kawashima, R. (2012). Beneficial effects of short-term combination exercise training on diverse cognitive functions in healthy older people: Study protocol for a randomized controlled trial. Trials, 13(1), 200. https://doi.org/10.1186/1745-6215-13-200
- Orsini, A., Grossi, D., Capitani, E., Laiacona, M., Papagno, C., & Vallar, G. (1987). Verbal and spatial immediate memory span: normative data from 1355 adults and 1112 children. Italian Journal of Neurological Sciences, 8(6), 539–548. https://doi.org/10.1007/bf02333660
- Pelemiš, V., Zoretić, D., & Prskalo, I. (2023). Physical performance and morphological characteristics of young basketball players before and after COVID-19. Children, 10(3), 493. https://doi.org/10.3390/children10030493
- Quan, M., Wang, X., Gong, M., Wang, Q., Li, Y., & Jia, J. (2023). Post-COVID cognitive dysfunction: Current status and research recommendations for high risk population. The Lancet Regional Health Western Pacific, 38, 100836. https://doi.org/10.1016/j.lanwpc.2023.100836
- Rass, V., Beer, R., Schiefecker, A. J., Kofler, M., Lindner, A., Mahlknecht, P., Heim, B., Limmert, V., Sahanic, S., Pizzini, A., Sonnweber, T., Tancevski, I., Scherfler, C., Zamarian, L., Bellmann-Weiler, R., Weiss, G., Djamshidian, A., Kiechl, S. … Helbok, R. (2021). Neurological outcome and quality of life 3 months after COVID-19: A prospective observational cohort study. European Journal of Neurology, 28(10), 3348–3359. https://doi.org/10.1111/ene.14803
- Saneemanomai, S. (2023). Cognitive functions among patients who recovered from COVID-19. Journal of Southeast Asian Medical Research, 7, e0145. https://doi.org/10.55374/jseamed.v7.145
- Scarpina, F., & Tagini, S. (2017). The stroop color and word test. Frontiers in Psychology, 8, 557. https://doi.org/10.3389/fpsyg.2017.00557
- Sekendiz, Z., Clouston, S. A. P., Morozova, O., Carr, M. A., Fontana, A., Mehta, N., Ali, A., Jiang, E., & Luft, B. (2023). Assessment and characterization of covid-19 related cognitive decline: Results from a natural experiment. medRxiv. https://doi.org/10.1101/2023.11.06.23298101
- Simonelli, C., Paneroni, M., Vitacca, M., & Ambrosino, N. (2021). Measures of physical performance in COVID-19 patients: A mapping review. Pulmonology, 27(6), 518–528. https://doi.org/10.1016/j.pulmoe.2021.06.005
- Voinsky, I., Baristaite, G., & Gurwitz, D. (2020). Effects of age and sex on recovery from COVID-19: Analysis of 5769 Israeli patients. The Journal of Infection, 81(2), e102–e103. https://doi.org/10.1016/j.jinf.2020.05.026
- Wang, F., Kream, R. M., & Stefano, G. B. (2020). Long-term respiratory and neurological sequelae of COVID-19. Medical Science Monitor: International Medical Journal of Experimental and Clinical Research, 26, e928996. https://doi.org/10.12659/msm.928996
- World Health Organization. (2024). COVID-19 Epidemiological Update. January 19, 2024. Retrieved 26 January 2024, from https://www.who.int/publications/m/item/covid-19-epidemiological-update—19-january-2024