Keywords
COVID-19 - vitamin B12 - olfactory dysfunction
Introduction
In December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2),
initially known as the 2019 novel coronavirus (2019-nCoV), started in China in Wuhan.
Since then, this novel virus, also named as coronavirus disease 2019 (COVID-19), has
crossed all countries' borders with dramatic spread all over the world until the World
Health Organization (WHO) defined it as a pandemic disease on March 11, 2020.[1]
The novel COVID-19 is presented mainly by lower respiratory tract-related manifestations
such as fever, cough, dyspnea, and chest tightness that could progress quickly to
acute respiratory distress syndrome (ARDS).[2] However, COVID-19 also leads to different upper respiratory tract-related manifestations
comprising sore throat, smell dysfunction, and nasal congestion.[3] The olfactory and gustative alterations are frequent in the initial stages of the
infection.[2]
[3]
[4]
[5]
Of note, a wide variation has been reported between Chinese and European studies regarding
the prevalence of taste and smell affection. In one Chinese study, anosmia and ageusia
were reported in 5.1% and 5.6% of patients, respectively.[6] In contrast, the frequency of taste and smell disorders in European studies ranged
between 19.4% and 88%.[2]
[3]
[4]
[5]
Vitamin B-12 deficiency is expected to result in low serum or plasma concentrations
of total vitamin B-12 and holotranscobalamin, accompanied by high methylmalonic acid
(MMA) and total plasma homocysteine (tHcy).[7] Severe vitamin B-12 deficiency is characterized clinically by megaloblastic anemia
and neurodegenerative changes of the central and peripheral systems. Neurological
effects may include cognitive impairment, peripheral neuropathy, subacute combined
degeneration of the spinal cord, and psychiatric disorders.[8]
[9]
[10]
The present study aimed to assess the relation between vitamin B12 levels and smell
affection in COVID-19 patients.
Methods
The present prospective study was conducted at a private hospital at the **BLINDED
FOR REVIEW PROCESS** between May 2020 and June 2021. The study protocol was approved
by the local ethics committee of **BLINDED FOR REVIEW PROCESS**, and all patients
signed an informed consent form before participation. The study included 201 COVID-19
patients with positive reverse-transcriptase polymerase chain reaction (RT-PCR) test
of a nasopharyngeal swab. Patients were excluded from the study if they had history
of smell dysfunction or nasopharyngeal or neurological disorders that may affect smell
function and were subjected to careful history taking, thorough clinical examination
and standard laboratory assessment.
The COVID-19 severity was assessed using the Infectious Diseases Society of America/American
Thoracic Society (IDSA/ATS) criteria. Patients were classified to have severe disease
if they had ≥ 1 major criterion (1. septic shock with need for vasopressors or 2.
invasive mechanical ventilation) or ≥ 3 minor criteria (1. respiratory rate ≥ 30 breaths/min.,
2. PaO2/FiO2 ratio ≤ 250, 3. multilobar infiltrates, 4. confusion/disorientation, 5. uremia (BUN
level ≥ 20 mg/dL), 6. leukopenia as a result of infection alone (WBC count < 4,000
cells/mL), 7. thrombocytopenia (platelets count < 100,000/mL), 8. hypothermia (core
temperature < 36°C), 9. hypotension requiring aggressive fluid resuscitation).[11]
Smell affection was quantitively assessed using the clinical test described by Cain
et al.[12] The test combines threshold testing and odor identification. According to the composite
score, patients were classified into five categories of functioning: normal osmesis,
mild hyposmia, moderate hyposmia, severe hyposmia, and anosmia. For convenience, we
classified our patients into three categories: normal osmosis, hyposmia (whatever
its severity), and anosmia. Evaluation of smell function was performed at baseline
and after 4 weeks of diagnosis. Serum vitamin B12 levels were assessed using commercial
enzyme-linked immunosorbent assay (ELISA) kits.
Data obtained from the present study were presented as mean and standard deviation
(SD) or number and percentage. Continuous variables were compared using the one-way
analysis of variance (ANOVA) with posthoc LSD comparisons. The cxategorical data were
compared using the chi-squared test. Correlation analysis was achieved using the Pearson
correlation analysis. A receiver operator characteristic (ROC) curve analysis was
used to identify diagnostic performance of investigated marker. All statistical tests
were performed using the IBM SPSS Statistics for Windows, version 25.0 (IBM Corp.,
Armonk, NY, USA). A p-value lower than 0.05 was considered statistically significant.
Results
The present study included 201 COVID-19 patients. According to smell function assessment,
the patients were classified into three categories: normal osmesis (n = 77), hyposmia (n = 49), and anosmia (n = 75) ([Fig. 1]). Four weeks later, 195 patients (97.0%) restored normal smell function. The remainder
six patients included four anosmic and two hyposmic patients.
Fig. 1 Smell affection in the studied patients.
The comparison between patients with and without smell affection regarding the clinical
and laboratory data revealed that patients with smell affection are significantly
younger that patients with normal sense of smell ([Table 1]). It was also shown that patients with hyposmia or anosmia had significantly lower
vitamin B12 levels when compared with patients with normal osmesis (median interquartile
range [IQR]: 363.0 [198.0–539.0] versus 337.0 [175.0–467.0] and 491.0 [364.5–584.5]
pg/ml respectively, p < 0.001). Also, anosmic patients were found to have significantly lower vitamin B12
levels in comparison to hyposmic counterparts ([Table 1], [Fig. 2]).
Table 1
Clinical and laboratory findings in the studies patients (n = 201)
|
All patients
N = 201
|
Normal osmesis
N = 77
|
Hyposmia
N = 49
|
Anosmia
N = 75
|
P-value
|
|
Age (years) median (IQR)
|
31.0 (27.0- 36.0)
|
33.0 (28.0–39.0)
|
32.0 (28.5–38.0)
|
30.0 (26.0–33.0)
|
0.003
|
|
Male/female n
|
132/69
|
47/30
|
35/14
|
50/25
|
0.48
|
|
Covid-19 severity n (%)
|
|
Mild
|
30 (14.9)
|
65 (84.4)
|
38 (77.6)
|
68 (90.7)
|
0.13
|
|
Severe
|
171 (85.1)
|
12 (15.6)
|
11 (22.4)
|
7 (9.3)
|
|
Laboratory findings median (IQR)
|
|
Hb (gm/dL)
|
13.0 (12.0–14.0)
|
12.8 (11.8–14.0)
|
13.0 (11.5–14.2)
|
13.2 (12.0–14.0)
|
0.27
|
|
WBCs (× 103/mL)
|
6.5 (4.5- 10.0)
|
6.5 (4.0–10.0)
|
6.0 (4.6–10.7)
|
7.0 (4.5–10.0)
|
0.44
|
|
Platelets (× 103/mL)
|
212.0 (162.5- 260.0)
|
200.0 (139.5–250.0)
|
200.0 (160.0–239.5)
|
215.0 (180.0–259.0)
|
0.17
|
|
CRP (mg/dL)
|
88.0 (44.5- 126.5)
|
91.0 (41.0–145.5)
|
93.0 (50.5–122.5)
|
75.0 (41.0–118.0)
|
0.42
|
|
Procalcitonin (µg/L)
|
0.1 (0.08- 0.2)
|
0.1 (0.1–0.2)
|
0.15 (0.08–0.2)
|
0.1 (0.08–0.2)
|
0.96
|
|
LDH (U/L)
|
614.0 (414.0- 908.0)
|
527.0 (385.5–922.5)
|
621.0 (454.5–911.5)
|
618.0 (431.0–831.0)
|
0.38
|
|
Ferritin (µg/L)
|
663.0 (442.0- 1,456.5)
|
648.0 (408.5–1,549.0)
|
800.0 (416.0–1,598.5)
|
713.0 (507.0–1,324.0)
|
0.65
|
|
PT (sec.)
|
13.9 (13.0–15.8)
|
14.3 (13.2–15.8)
|
14.8 (13.3–16.7)
|
14.5 (13.0–16.0)
|
0.36
|
|
APTT (sec.)
|
34.0 (30.0–42.0)
|
35.0 (31.0–40.5)
|
36.0 (32.0–45.5)
|
33.0 (30.0–44.0)
|
0.27
|
|
D-dimer (ng/mL)
|
1162.0 (746.5- 2,122.0)
|
978.0 (732.0–2,122.0)
|
1290.0 (810.0–2,549.0)
|
980.0 (750.0–1,750.0)
|
0.35
|
|
Fibrinogen (gm/dL)
|
3.7 (3.0- 4.8)
|
3.7 (3.1–4.7)
|
4.1 (3.0–5.2)
|
3.5 (3.0–4.5)
|
0.23
|
|
Creatinine (mg/dL)
|
1.1 (0.8- 1.3)
|
1.0 (0.9–1.3)
|
0.9 (0.9–1.25)
|
0.9 (0.8–1.3)
|
0.1
|
|
Urea (mg/dL)
|
50.0 (38.0–76.0)
|
51.0 (38.0–76.5)
|
56.0 (41.0–80.0)
|
45.0 (37.0–72.0)
|
0.42
|
|
Albumin (gm/dL)
|
3.2 (3.0- 4.0)
|
3.5 (3.0–3.9)
|
3.5 (3.1–3.8)
|
3.5 (3.1–4.0)
|
0.88
|
|
AST (U/L)
|
45.0 (29.0–72.5)
|
47.0 (34.5–76.0)
|
41.0 (28.0–76.0)
|
42.0 (27.0–67.0)
|
0.19
|
|
ALT (U/L)
|
51.0 (34.0- 80.0)
|
59.0 (37.0–81.0)
|
48.0 (33.0–80.0)
|
44.0 (26.0–76.0)
|
0.08
|
|
O2 saturation (%)
|
90.0 (80.0- 95.0)
|
92.0 (80.0–95.0)
|
90.0 (80.0–94.0)
|
92.0 (85.0–95.0)
|
0.07
|
|
Vitamin B12 (pg/mL)
|
403.0 (212.0- 544.5)
|
491.0 (364.5–584.5)
|
363.0 (198.0–539.0)
|
337.0 (175.0–467.0)
|
< 0.001
|
Abbreviations: aPTT, activated partial thromboplastin time; ALT, alanine aminotransferase;
AST, aspartate aminotransferase; CRP, c-reactive protein; Hb, hemoglobin; IQR, interquartile
range; LDH, lactate dehydrogenase; PT, prothrombin time; WBCs, white blood cells.
Fig. 2 Vitamin B12 levels in the studied patients.
The correlation analysis identified no significant correlation between vitamin B12
levels and other laboratory or clinical parameters ([Table 2]). The ROC curve analysis showed good performance of vitamin B12 levels in identification
of smell affection in COVID-19 patients (area under de curve [AUC] 95% confidence
interval [95% CI]: 0.69 [0.61–0.76]) with a sensitivity and specificity of 67.7% and
63.6%, respectively ([Fig. 3]).
Fig. 3 Receiver operating characteristics curve for vitamin B12 in detection of smell affection.
Table 2
Correlation between vitamin B12 levels and the clinical and laboratory data
|
Vitamin B12
|
|
Age
|
0.12
|
0.17
|
|
Hb
|
0.04
|
0.61
|
|
WBCs
|
-0.07
|
0.35
|
|
Platelets
|
0.09
|
0.19
|
|
CRP
|
0.04
|
0.56
|
|
Procalcitonin
|
0.03
|
0.71
|
|
LDH
|
−0.03
|
0.67
|
|
Ferritin
|
−0.04
|
0.6
|
|
PT
|
−0.04
|
0.58
|
|
APTT
|
0.02
|
0.82
|
|
D-dimer
|
−0.03
|
0.7
|
|
Fibrinogen
|
0.11
|
0.06
|
|
Creatinine
|
0.14
|
0.056
|
|
Urea
|
0.06
|
0.41
|
|
Albumin
|
0.1
|
0.08
|
|
AST
|
−0.08
|
0.26
|
|
ALT
|
0.11
|
0.07
|
|
O2 saturation
|
−0.07
|
0.27
|
Abbreviations: ALT, alanine transaminase; APTT, activated partial thromboplastin time;
AST, aspartate aminotransferase; CRP, c-reactive protein; LDH, lactate dehydrogenase;
Hb, hemoglobin; O2, oxygen; PT, prothrombin time; WBCs, white blood cells.
Discussion
In the present study on 201 COVID-19 patients, 124 patients (61.7%) had some degree
of smell affection. They comprised 49 patients (24.4%) with hyposmia and 75 patients
(37.3%) with anosmia. In comparison, one study from Saudi Arabia noted that olfactory
dysfunction was reported by 53% of COVID-19 patients, of which 32.7% were anosmic
and 20.3% were hyposmic.[13] In another study, anosmia was diagnosed in 44.0% of 500 COVID-19 patients from the
United Arab Emirates,[14] while anosmia was reported in 67.0% of 288 Brazilian COVID-19 patients.[15] One large meta-analysis including data from 107 studies and 32,142 COVID-19 patients
found that anosmia was reported in 12,038 patients with a prevalence of 38.2% (95%
CI: 36.5%, 47.2%).[16] This variation may be explained by the different tools used for diagnosis of olfactory
dysfunction in different studies. In addition, other clinical or genetic factors may
be involved.
Four weeks later, 195 patients (97.0%) had their normal smell function resotred. The
remainder six patients included four anosmic and two hyposmic patients. In the study
of Babaei et al.,[17] 88.5% of patients had their sense of smell restored by 4 weeks, while in the study
of Kumar et al.,[18] 97.0% of patients recovered it within 2 weeks.
Interestingly, the present study found that patients with smell affection were significantly
younger than patients with normal smell, which is in line with the former study of
Mubaraki et al.[13]
In this study, we assessed the relation between vitamin B12 levels and smell affection
scores in COVID-19 patients. In the first and 4 weeks, groups with higher vitamin
B12 levels had significantly better self-rated smell affection scores.
The association between vitamin B12 deficiency and smell affection was previously
reported. The study of Derin et al.[19] showed a relation between vitamin B12 deficiency and olfactory dysfunction. Interestingly,
one recent report recognized good response of COVID-19 patients with olfactory affection
to vitamin B12 supplementation.[20]
The mechanisms explaining the role of vitamin B12 in olfactory dysfunction remain
to be elucidated. However, the main suggested mechanism is olfactory neuronal toxicity
caused by elevated homocysteine levels due to inefficient methylation of homocysteine
into methionine in patients with vitamin B12 deficiency.[21]
[22]
Conclusion
In conclusion, vitamin B12 appears to have some contribution to smell affection in
patients with COVID-19 infection. The findings of the present study may have significant
clinical implications, particularly in patients with long-term post-COVID-19 infection.
The assessment of vitamin B12 levels in those patients may provide a clue for appropriate
treatment. However, the value of vitamin B12 supplementation as a therapeutic strategy
requires well-designed randomized clinical studies to be confirmed.
