Vitamin D Deficiency and Its Association With Anemia and Blood Transfusion Requirements in Nigerian Adults With Sickle Cell Anemia

Abstract

Background

Vitamin D supplementation has been shown to improve hemoglobin levels in patients with sickle cell anemia (SCA). However, very little is known about the prevalence of its deficiency, its role in hemolysis, and its effects on transfusion requirements in SCA, hence this study.

Patients and Methods

Serum level of vitamin D was determined in 50 SCA patients in steady state, 50 SCA patients in hemolytic crises, and 50 in normal HbAA individuals. All were 18 years or older and were age- and sex-matched. In addition, PCV and hemoglobin (Hb) concentration, absolute reticulocyte count, uric acid, total and conjugated bilirubin, creatinine, lactate dehydrogenase (LDH), and estimated glomerular filtration rate (eGFR) were also assessed in all subjects and controls. Baseline sociodemographic, clinical, and anthropometric data were also recorded.

Results

The prevalence of vitamin D insufficiency and deficiency was found to be 18% and 79%, respectively. The mean serum levels of vitamin D were 18.84 ± 6.86 ng/mL and 17.58 ± 6.23 ng/mL in the steady-state and the hemolytic crises SCA groups, respectively. Transfusion requirements were found to be higher in SCA patients with lower vitamin D levels. Unlike those in crisis who received one or more units of blood transfusion, 42% of those in the steady state did not receive blood transfusion over the same period of 12 months. Hemoglobin levels were, however, found to predict reduced vitamin D levels.

Conclusion

Vitamin D deficiency (VDD) is highly prevalent among adults with SCA and those with lower vitamin D levels are more anemic and hence may require more blood transfusions.

Keywords

Sickle cell anemia vitamin D deficiency anemia increased blood transfusion requirements

Introduction

Sickle cell disease (SCD) is an inherited disorder in which an individual inherits abnormal hemoglobin S (HbS) either in the homozygous form sickle cell anamia (HbSS) or in heterozygous form with another abnormal hemoglobin such as sickle cell–hemoglobin C disease (HbSC) or sickle/beta thalassemia (HbS/β thalassemia.).¹ Sickle cell anemia (SCA) is the most clinically severe form; however, some individuals affected by this condition may not be aware of it until they develop a sickle cell crisis which manifests as vaso-occlusive events, leading to episodic ischemia/necrosis called “crises.” Crises may cause severe organ damage affecting the brain, skeleton, pulmonary vasculature, spleen and liver, resulting in increased morbidity and mortality.² The prevalence of SCA is high in the Nigerian population³ with a frequency of 3% and an estimated new bath of 150,000 annually.⁴ Although there are reports in the literature on the role of vitamin D on chronic pain in patients with SCA,⁵ there is limited data on its role in hemolysis. Vitamin D intake has been shown to reduce episodes of chronic pain in SCA patients⁶ and correlated positively with increasing hemoglobin levels.⁷ Vitamin D has also been shown to directly increase erythropoietin sensitivity in patients with renal disease⁸, and its deficiency which causes hyperparathyroidism inhibits endogenous production of erythropoietin⁹, hence, may cause anemia. Vitamin D deficient states may be due to several factors including poor nutrition or fat malabsorption.¹⁰ There may be damage to the intestinal mucosa leading to poor absorption of nutrients.¹¹ A high incidence of renal impairment in patients with SCA may contribute to low vitamin D levels by its metabolism to the active form. ¹² Vitamin D has been found to have a role in marrow function.¹³ It has been shown that vitamin D repletion resulted in using lower doses of erythrocyte-stimulating agents and increasing reticulocytosis.¹⁴ Vitamin D administration has been associated with an improvement in anemia.¹⁵ Vitamin D deficiency (VDD) has been linked to anemia in SCA patients.¹⁶

Globally, the prevalence of VDD among adults with SCA is as high as 60% to 100%.³ Despite the huge burden of adults with SCA in Nigeria, published data on the burden of VDD in Nigeria is limited. The knowledge of the prevalence of VDD among Nigerian adults with SCA and its effects on hemolysis and transfusion requirements in these patients may provide new insights and provide evidence-based guidelines on how to appropriately supplement Vitamin D in this at-risk population. Therefore, this study assessed the prevalence of hypovitaminosis D and its relationship with lower hemoglobin levels and increased transfusion requirements in Nigerian adults with SCA.

Patients and Methodology

This cross-sectional prospective study was conducted at the Haematology Clinic of the Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC), Ile-Ife over a period of 1 year. The study population comprised of patients with homozygous for hemoglobin S (HbSS or SCA) diagnosed using hemoglobin electrophoresis and who were between the ages of 18 and 60 years and in steady state. The sample size was calculated using Kish-Leslie formula¹⁷ based on the prevalence of SCA in Nigeria of 3% as reported by Akinyanju.¹⁸ The sample size obtained by calculation was 50 with a 10% attrition rate. Two control groups of 50 normal HbAA individuals and 50 SCA patients in hemolytic crises were also recruited. SCA patients in hemolytic crisis are those with increased numbers in red cell destruction over a short period manifesting with a drop in hemoglobin level and feeling of weakness and tiredness, hyperbilirubinemia, yellowness of the sclera, and in other mucous membranes, among others manifestations. They were all age- and sex-matched. All SCA patients were on routine antimalaria prophylaxis paludrine (200 mg daily), folic acid (5 mg daily), and vitamin B complex (one tablet three times daily). SCA patients with liver disease on hydroxyurea, vitamin D supplements, anticonvulsant, or on chronic blood transfusions were excluded. The eligible subjects who consented were recruited consecutively until the sample size for the study group and the two control groups were completed. Indications for blood transfusion in SCA patients were noted. The study was approved by the Ethics and Research Committee of the hospital (ERC/2018/03/12). Informed consent was obtained from all recruited subjects. The control subjects were recruited from eligible blood donors who have been screened and found negative for transfusion transmissible infectious viruses (hepatitis B and C and human immunodeficiency viruses and syphilis)

A structured proforma was used to collect sociodemographic data about each recruited subject including age at diagnosis of SCA, age at menarche, date of last crisis, date of last blood transfusion, frequency of blood transfusions per year, frequency of use of routine drugs, and 24 hours dietary recall. Bodyweight to the nearest kilogram was measured using an analogue weighing scale (RT-160 Ledial Medical Ltd) and height was measured using a stadiometer. (RT-160 Ledial Medical Ltd). The body mass indexes (BMIs) were calculated using weight (kg)/height (m). Vitamin D intake in 24 hours was calculated from a 24-hour dietary recall. The recommended daily allowance for vitamin D in both men and women older than 18 years is 600I.U (15mcq)¹⁹. Selected food sources of vitamin D were cod liver oil, swordfish, salmon, tuna, sardine, egg yolk, Swiss cheese, fortified yoghurt, butter, and cereals²¹ and the quantity in them were calculated using the vitamin D fact sheet.²¹ Selected food sources of vitamin D were cod liver oil, swordfish, salmon, tuna, sardine, egg yolk, Swiss cheese, fortified yoghurt, butter, and cereals

Ten mL of venous blood was drawn from each study participant, 3 mL was placed in an EDTA bottle for PCV, hemoglobin, reticulocyte count, and peripheral blood film examination. The second 3 mL was placed in a lithium heparin bottle for total and conjugated bilirubin assay and uric acid assay. The last 4 mL was placed in a plain bottle for serum lactate dehydrogenase (LDH) assay.

Packed cell volume and hemoglobin concentration were measured using the automated blood cell analyzer (Sysmex CX-21). The reticulocyte percentage was manually done while the absolute reticulocyte count is calculated. Serum bilirubin and LDH levels were measured using a spectrophotometer.

Haptoglobin was analyzed using competitive enzyme-linked immunosorbent assay (ELISA) that measures its residual peroxidase activity using a spectrophotometer. Reference range is 50 to 220 mg/dL. Urinalysis was done using Mission Expert (U034-101) urinalysis strips which use tetrabromophenol blue as an indicator to detect albuminuria as low as 0.12 to 0.15 g/L

The assay of vitamin D was done using a 25(OH)D ELISA kit which has a sensitivity of 94.2% and specificity of 98.8%. Vitamin D status was classified²² as sufficient if serum 25(OH)D is ≥30 ng/mL, insufficient if serum 25(OH)D is between 20 and 29 ng/mL, deficient if serum 25(OH)D is 10 and 19 ng/mL, severely deficient if serum 25(OH)D is less than 10 ng/mL using the Endocrine Society Clinical Practice guidelines.

Statistical Methods

Data were expressed as mean ± SD for parametric data and median (interquartile range) for nonparametric data. The obtained data were analyzed using descriptive and inferential statistics. An independent t-test was used to analyze the continuous variables. ANOVA was used to analyze the group data. The level of relationship between parameters was determined using Pearson's correlation. Linear regression analysis was used to determine the clinical or biochemical parameters that are independently associated with hypovitaminosis D. P-values ≤ 0.05 defined statistical significance and adjusted odds ratio with 95% Confidence Interval was considered to have an association. Linear regression analysis was used to determine which of the variables were independent predictors of low vitamin D levels.

Results

Demographic Parameters of Subjects

Table 1 shows the sociodemographic characteristics of the study population. The mean age of subjects and controls was 27.92 ± 8.8 with a male-to-female ratio of 1:1.4. There were no statistically significant differences in the age and gender distribution of the three groups. The mean BMI of the SCA patients in steady state was 20.04 ± 3.9 mg/m², that of the SCA in crises was 19.66 ± 3.0 mg/m² while that of the HbAA group was 25.35 ± 3.8 mg/m². Fifteen (30%) of the SCA patients in steady state were underweight, 32(64%) had normal BMIs, 1 (2%) were overweight, and only 2 (4%) were obese. For the HbAA controls, none were underweight, 27 (54%) had normal BMIs, 14 (28%) were overweight, and only 9 (18%) were obese. For the SCA subjects in hemolytic crises, 14 (28%) were underweight, 34 (68%) were of normal BMI, 2 (4%) were overweight, and none of them was obese. Severe anemia post-hemolytic crisis and vaso-oclusive were the main indications for blood transfusion in SCA subjects that received a blood transfusion.

Table 1.

Gender and Body Mass Distribution in the Groups.

	SCA in steadystate (n=50)	HbAA(n=50)	SCA in crises(n=50)	Total
Gender
Male	21 (42.0%)	21 (42.0%)	21 (42.0%)	63 (42.0%)
Female	29 (58.0%)	29 (58.0%)	29 (58.0%)	90 (58.0%)
BMI (mg/m²)
Underweight	15 (30.0%)	0 (0.0%)	14 (28.0%)	29 (19.3%)
Normal	32 (64.0%)	27 (54.0%)	34 (68.0%)	93 (62.0%)
Overweight	1 (2.0%)	14 (28.0%)	2 (4.0%)	17 (11.3%)
Obesity	2 (4.0%)	9 (18.0%)	0 (0.0%)	11 (7.3%)
Mean ± SD	20.04±3.9	25.35±3.8	19.66±3.0

Abbreviations: BMI, body mass index; SCA, sickle cell anemia.

Prevalence of Hypovitaminosis D

The prevalence of vitamin D insufficiency and deficiency was found to be 18% and 79%, respectively. Table 2 shows the mean ±SD, median, and interquartile range for serum 25(OH)D among the three groups. Four (8%) of the SCA patients in steady state were severely deficient, 25 (50%) were deficient, 18 (36%) were insufficient while only 3 (6%) had optimal vitamin D levels. In the hemolytic crisis group, 5 (10%) were severely deficient, 26 (52%) were deficient, and 19 (38%) had insufficient vitamin D levels. The reference ranges used were 0 to 10 ng/mL (severely deficient), 11 to 20 ng/mL (deficient), and 21 to 30 ng/mL (insufficient). Mean vitamin D levels in the SCA in the steady-state group was 18.84 ± 6.9 ng/mL, while those in hemolytic crisis had a mean value of 17.58 ± 6.23, both of which were significantly lower than that of the HbAA controls which had mean vitamin D levels of 48.10 ±10.1(p = 0.0001). All the HbAA controls had serum vitamin D levels above 30 ng/mL.

Table 2.

Comparison of Biochemical Markers of Hemolysis in the Groups.

	SCA(steady state)(n=50)	HbAA(NC)(n=50)	SCA(crisis)(n=50)	Statistics
Hematological parameters	Mean ± SD	Mean ± SD	Mean ± SD	F value p value
PCV (%)	23.30 ± 3.1	39.90 ± 5.7	19.88 ± 2.2	368.342; < 0.001
Hb (g/dL)	8.24 ± 1.1	14.03 ± 2.1	6.82 ± 1.0	334.417; < 0.001
Retics (%)	4.52 ± 0.5	1.29 ± 0.3	7.27 ± 1.3	704.777; < 0.001
ARC (cell/cmm)	135.23 ± 22.5	65.41 ± 13.1	172.31 ± 51.5	217.724; < 0.001

Vitamin D	Mean ± SD	Median (IQR)	Statistics	p value
HbAA (control)	48.10 ± 10.12	48.7 (39-55.2)	KW (χ2) = 99.33	0.0001
SCA (crisis)	17.58 ± 6.23	17.5 (13-21.2
SCA (steady state)	18.84 ± 6.86	19.2 (13.6-22.4)

Biochemical parameters	Median(Q1, Q3)	Median(Q1, Q3)	Median(Q1, Q3)	K value	p value
LDH (I.U/L)	69.0(56.0, 82.0)	17.0(13.0, 18.0)	119.0(92.0, 132.0)	123.707	<0.001*
Uric acid (mg/dL)	0.36(0.3, 0.4)	0.26(0.2, 0.3)	0.25(0.2, 0.3)	19.702	<0.001*
Total bilirubin (mg/dL)	37.0(27.0, 61.0)	8.0(8.0, 9.0)	51.5(38.0, 75.0)	103.040	<0.001*
Unconjugated bilirubin (mg/dL)	20.5(16.0, 41.0)	6.0(6.0, 7.0)	30.5(25.0, 50.0)	92.874	<0.001*
	Mean ± SD	Mean ± SD	Mean ± SD	F value	p value
Creatinine (µmol/L)	58.04 ± 8.6	73.24 ± 11.8	67.36 ± 10.0	28.290	< 0.001*
eGFR (mL/min/1.73 m²)	114.98 ± 21.4	111.61 ± 8.6	98.83 ± 14.2	14.937	< 0.001*
Multiple linear regression analysis of the determinants of vitamin D
Variable	Correlation	95% confidence interval		p value
		Upper limit	Lower limit	p value
Absolute retic	0.00004	−0.000011	0.00010	0.11
Hb concentration	−1.09	−2.01	−0.17	0.020
Retic percentage	−0.81	−2.75	1.12	0.41
LDH	−.041	−0.11	0.027	0.24
Uric acid	−8.07	−19.77	3.64	0.18
Total bilirubin	0.001	−0.022	0.024	0.93
Unconjugated bilirubin	−.017	−0.099	0.064	0.67
HbAA (control)
SCA (steady state)	−32.90	−41.57	-24.23	<0.001
SCA (crisis)	−33.70	−46,98	-20.40	<0.001

Abbreviations: ARC, absolute reticulocyte count; eGFR, estimated glomerular filtration rate; Hb, hemoglobin concentration; HbAA, normal HbA; PCV, packed cell volume; Retics, reticulocyte count;; SCA (SS), sickle cell anemia in steady state; SCA (CR), sickle cell anemia in crisis; LDH, lactate dehydrogenase.

Hematological Parameters

Table 2 shows the hematological and biochemical parameters of patients in the three groups. The PCV and hemoglobin (Hb) concentration of the SCA patients in steady-state and the SCA in the hemolytic crises group were 23.30 ± 3.1%, 8.24±1.1 g/dL, and 19.88 ± 2.2% and 6.82 ± 1.0, respectively. The PCV and Hb concentration for these two groups were significantly lower compared to those of healthy HbAA controls (p < 0.001). The PCV and Hb concentration of the HbAA healthy controls was 39.90 ± 5.7% and 14.03 ± 2.1 g/dL. The reticulocyte percentage and absolute reticulocyte count of the SCA in the steady-state group were significantly higher (p <0.001) than that of the HbAA group which had a mean reticulocyte percentage of 1.29 ± 0.3% and a mean absolute reticulocyte count of 65.41 ±.13.1×10³cells/mm². The median (Q1, Q3) values of LDH in the subjects with SCA patients in a steady state was 69.0(56.0, 82.0) where Q1 and Q3 are the 25th and 75th percentiles, respectively. The median value of LDH in the SCA in hemolytic crises was higher with a value of 119.0 (92.0, 132.0). The median value of LDH in the healthy HbAA controls was significantly lower (p = < 0.001) than that of the SCA in either steady-state or hemolytic crises with a value of 17.0 (13.0, 18.0). A comparison of the LDH across the three groups gave a significant K value of 123.707 (p < 0.001) Similarly, the median values of uric acid, total bilirubin, and unconjugated bilirubin for the SCA in steady-state and hemolytic crises were significantly higher (p < 0.001) than the median values for uric acid, total bilirubin, and unconjugated bilirubin in the HbAA healthy controls. Serum creatinine levels and estimated glomerular filtration rate (eGFR) values (using CKD-EPI formula) in the three groups were within acceptable ranges.

The multivariate regression analysis to determine the relationship between vitamin D and some hemolytic markers showed that hemoglobin concentration is the only variable with a significant relationship with vitamin D. Patients in the SCA in steady-state groups have lower levels of vitamin D than the HbAA control group (reference group). (β = −27.85, 95% CI = −35.54 to −20.17, p = <0.001). Similarly, patients with SCA in crisis also have a significantly lower level of vitamin D than the HbAA control group. (β = −33.7, 95% CI = −46.98 to −20.40, p = <0.001). Overlapping confidence intervals between the two SCA groups suggests no difference between the vitamin D levels in them.

In the SCA patients in steady state, only 29 (58%) of the 50 patients received a blood transfusion in the previous year. The mean vitamin D levels among the transfused SCA patients in a steady state was 16.7 ± 6.92 ng/mL which was significantly lower than the mean vitamin D levels (21.73 ± 5.75 ng/mL) of the steady-state SCA patients who did not require transfusion in the previous year (p = 0.0092). The SCA subjects that received blood transfusion had higher vitamin D levels compared to those that did not receive a blood transfusion. Hemolytic and vaso-oclusive crises were the main reasons for blood transfusion in them. In SCA that were in steady state, 42% did not receive a blood transfusion, while 50% and 8% received one unit and two units of blood, respectively, while 82%, 16%, and 2% received one, two and three units of blood, respectively.

Table 3 shows a comparison of the vitamin D intake of the subject and control groups gotten from a 24-hour dietary recall. It can be observed from the table that the majority (36 or 62%) of the SCA in the steady-state group took vitamin D-rich foods only once a day while only a small portion of 12(24%) subjects took vitamin D-rich foods more than once a day and 2 (4%) of them did not take vitamin D-rich foods daily. For the SCA in the hemolytic crises group, the largest bulk (19 or 38%) took vitamin D-rich foods occasionally, 18 (36%) of them took vitamin D-rich foods more than once daily while 13 (26%) took vitamin D-rich foods once daily. For the healthy HbAA controls, the large bulk of them (40 or 80%) had a constant daily supply of vitamin D as their intake of vitamin D-rich foods was from several sources incorporated into more than one meal, only 10 (20%) of them took vitamin D-rich foods just once a day.

Table 3.

Comparison of Intake of Vitamin D-rich foods.

Intake of vitamin D-rich foods	SCA in steady state	HbAA	SCA in hemolytic crises
Greater than once per day	12(24%)	40(80%)	18(36%)
Once per day	36(62%)	10(20%)	13(26%)
Less than once per day	2(4%)	0	19(38%)

Abbreviation: SCA, sickle cell anemia.

Discussion

The prevalence rate of vitamin D in this cohort of SCA patients in steady state was 90% out of which 56% had insufficient and 44% were deficient in vitamin D. This is similar to the findings by Goodman²¹ and Arlet²² who found a 100% prevalence of suboptimal vitamin D levels in their SCD patients. Arlet and colleagues also found from their studies that there were seasonal variations in vitamin D levels as vitamin D levels were lower in winter months and higher during the summer months.²² However, the seasonal variation could not be a factor in this cohort of subjects as all were domiciled within the tropical environment where they receive sunlight all the year-round and this may affect the serum levels of vitamin D found in this cohort of subjects studied. However, several reasons have been put forward to explain the high prevalence of VDD in SCA patients when compared to their non-SCA counterparts. These include their low BMI and body fat as vitamin D is a fat-soluble vitamin,¹⁰ increased resting metabolic rate, poor intestinal absorption of vitamin D, and other micronutrients due to gut microinfarction¹¹ impaired conversion of 25(OH)D to 1,25(OH)D in the kidneys due to repeated kidney microinfarctions.¹² Despite the normal serum creatinine and eGFR observed in the SCA patients in the steady state included in this study, the high degree of proteinuria indicates an impaired renal function which translates to some degree of impaired renal 1,25 hydroxylation of vitamin D to its active form in these patients.²³ Diet may be responsible for the high prevalence of VDD found in the SCA in steady-state patients studied. Seventy two percent took vitamin D-rich foods only once a day compared to their age and sex-matched healthy HbAA controls in which 80% took vitamin D-rich foods more than once a day. However, since the HbAA controls were recruited from hospital staff, they most probably were more enlightened about the benefits of eating a balanced diet and thus tended to include fish, liver, and eggs (vitamin D-rich foods) in most of their daily meals. However, the actual proportion of vitamin D being ingested in each meal could not be quantified due to the nonavailability of a clear and integrated local software for Nutrition Data System for Research (NDSR) which is needed to estimate dietary vitamin D from a 24-hour dietary recall.

In this study, a decrease in hemoglobin concentration and hematocrit levels were noted with decreasing serum vitamin D levels and a statistically significant increase in reticulocyte count and serum LDH concentrations with decreasing vitamin D levels. However, a direct causal link could not be established between vitamin D levels and the biomarkers of hemolysis. The lower serum vitamin D might, perhaps, have a protective role in the patients by reducing hematocrit and, hence, blood viscosity and consequently a reduction in vaso-oclusive episodes. A possible link between mutations that affect the Klotho protein gene expression has been suggested as a cause of lower vitamin D in patients with SCD. Defect in the Klotho gene protein has been implicated in the onset of osteonecrosis, priapism, leg ulcer, reduction in vitamin D synthesis, and depletion of nitric oxide in patients with SCD as a result of oxidative stress and endothelial impairment.²⁴ Similarly, lower plasma levels of protein C, free protein S, and nitic oxide but higher plasma levels of endothelin 1 and adrenomedullin have been associated with increased thrombotic risks^25,26

Multiple linear regression analysis of the data obtained revealed that only hemoglobin concentration had a significant correlation with vitamin D. This is similar to the findings by Park et al who noted that in children with SCA, lower hemoglobin levels seemed to be predictive of more severe vitamin D deficiency.²⁷ This present study also observed that the mean serum vitamin D levels among SCA patients in the steady state who had received a transfusion in the previous year were significantly lower than the mean vitamin D levels of patients with SCA in the steady state who did not require transfusion in the previous year. Also, Brown et al have observed that patients with both SCD and VDD were more likely to have at least one emergency room visit, at least one admission for pain crisis, and a longer admission compared to patients with SCD and sufficient vitamin D levels.²⁸ These findings were similar to the study by Adegoke et al who then suggested that supplementation of vitamin D in SCD may reduce their frequency of transfusions and improve their hemoglobin levels.¹² Busse et al, however, had a contrary view as their study showed no significant difference between the transfusion requirements of vitamin D insufficient and vitamin D sufficient SCA patients.²⁹ However, lower serum levels of vitamin D might have a protective role in SCA by reducing hematocrit level and as such a reduced plasma viscosity. Therefore, further studies are needed on the effects of vitamin D on vaso-oclusive crisis in patients with SCA.

Conclusion

SCA is characterized by chronic hemolysis with affected patients and occasionally requiring transfusion in cases of severe hemolysis or sequestration. Transfusion requirements from this study were observed to be increased in SCA patients with deficient and severely deficient vitamin D levels. Although this study suggests that low VDD levels are associated with increased transfusion requirements in SCA patients, there is a need for prospective and larger studies comparing vitamin D supplements to arrive at this conclusion.

Footnotes

Acknowledgements

The authors acknowledge with thanks the consent of our patients to take part in the study.

Authors’ Contributions

The concept of the study was by Salawu and Owojuyigbe; data acquisition, analysis, and manuscript preparation were by Salawu, Ochogwu, and Owojuyigbe; manuscript review and approval of the final draft were by Salawu, Ochogwu, Owojuyigbe, and Adedeji.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The funding of the study was borne by the authors.

Statement of Ethics

The study was approved by the Ethics and Research Committee of the hospital (ERC//2018/03/12).

ORCID iD

Lateef Salawu

References

Piccin

Fleming

Eakins

McGovern

Smith

McMahon

. Sickle cell disease and dental treatment. J Ir Dent Assoc. 2008;54(2):75-79.

Piccin

Murphy

Fleming

, etal. Insight into the complex pathophysiology of sickle cell anaemia and possible treatment. European J Haematology. 2019;102(4):319-330. doi: 10.1111/ejh.13212

Kaushansky

Lichtman

Beutler

Kipps

Uri

Prichal

. Disorders of Haemoglobin Structure: Sickle Cell Anaemia and Related Abnormalities. In: Agarwal

Alexandrescu

Agarwal

(eds). USA: McGraw Hill Companies Inc; 2010; 1(2): 56-62.

World Health Organisation. Provisional agenda Item: Sickle Cell Anaemia. 2006: 59(A59) www.who.int. Accessed on 4/6/18

Osunkwo

Zeigler

Alvarez

, et al. High Dose Vitamin D Therapy for Chronic Pain in Children and Adolescents with Sickle Cell Disease: Results of a Randomized Double-Blind Pilot Study. Br. J. Haematol. 2012;159(2):211-215.

Osunkwo

. Complete Resolution of Sickle Cell Chronic Pain with High-dose Vitamin D Therapy: A Case Report and Review of the Literature. J. Paed. Haematol. 2011;33(7):549-551.

Chennamashetti

Muley

. A study of Vitamin D deficiency in patients of sickle cell disease and its association with severity. Int J Adv Med. 2020;7(4):621-625.

Zeigler

Acquah

Tangpricha

. Vitamin D deficiency and chronic pain in sickle cell disease. Br J Haematol. 2011;53(4):538-540.

Adegoke

Braga

Adekile

, et al. The Association of Serum 25-Hydroxyvitamin D with Biomarkers of Hemolysis in Paediatric Patients with Sickle Cell Disease. Paed. Int. Child. Health. 2017;37(3):217-221.

10.

Julka

Aduli

Lamps

Olden

. Ischaemic Duodenal Ulcer, an Unusual Presentation of Sickle Cell Disease. Natl Med Assoc. 2008;100(15):339-341.

11.

Nath

Hebbel

. Sickle Cell Disease: Renal Manifestations and Mechanisms. Nat Rev Nephrol. 2015;11(3):161-171.

12.

Sim

Lac

Liu

, et al. Vitamin D Deficiency and Anaemia: A cross-sectional study. Ann Haematology. 2010;89(3):447-452.

13.

Thomas

Guilet

Queenan

, et al. Vitamin D Status is Inversely Associated with Anemia and Serum Erythropoietin During Pregnancy. Am J Clin Nutr. 2015;102(5):1088-1095.

14.

Smith

Vin Tangpricha

. Vitamin D and Anemia: Insights into an Emerging Association. Curr Opin Endocrinol Diabetes Obes. 2015;22(6):432-438.

15.

Domenico

Caccamo

Lucisano

, et al. Interplay of Vitamin D, Erythropoiesis and the Renin-Angiotensin System. Biomed Res. Intl. 2015;55(10):828-840.

16.

Boettger

Knupp

Liles

Walker

. Vitamin D deficiency in Adult with Sickle Cell Disease. Journal of the National Medical Association. 2017;109(1):36-43.

17.

Araoye

. Research Methodology with Statistics for Health and Health Sciences. Research Methodology. Volume 5. Nigeria: Nathadox Publishers; 2004;3(1):115-129.

18.

Akinyanju

. A Profile of Sickle Cell Disease in Nigeria. Ann NY Acad of Science. 1989;565(3):126-136.

19.

Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. National Academy Press; 2010.

20.

Dampier

LeBeau

Rhee

, et al. Health-related quality of life in adults with sickle cell disease (SCD): a report from the comprehensive sickle cell centres clinical trial consortium. Am J Haematol. 2011;86(2):203-205.

21.

Goodman

3rd Artz

Radford

Chen

. Prevalence of Vitamin D Deficiency in Adults with Sickle Cell Disease. J Natl Med Assoc. 2019;102(2):332-335.

22.

Arlet

Courbebaisse

Chateller

, et al. Relationship between Vitamin D Deficiency and Bone Fragility in Sickle Cell Disease, a Cohort Study 56 Adults. Bone. 2013;52(5):206-221.

23.

Bolarinwa

Akinlade

Kuti

Olawale

Akinola

. Renal Disease in Adult Nigerians with Sickle Cell Anaemia. Saudi J Kidney Transpl. 2012;23(1):171-175.

24.

de Souza Pacheco

APA

Gonclave

. Klotho: its various functions and association with sickle cell disease sub-phenotypes. Brazilian J. Haematology and Haemotherapy. 2014;36(6):430-436.

25.

Piccin

Murphy

Eakins

, etal. Protein C and free protein S in children with sickle cell anaemia. Ann Hematol. 2012; 91(10):1669-1671. doi: 10.1007/s00277-012-1447-9

26.

Piccin

Murphy

Eakins

Kunde

Corvetta

Di Pierro

Negri

Guido

Sainati

McMahon

Smith

Murphy

. Circulating microparticles, protein C, free protein S and endothelial vascular markers in children with sickle cell anaemia. J Extracell Vesicles. 2015;23(4):28414. doi: 10.3402/jev.v4.28414

27.

Park

Rebecca

Ogiteni

. Baseline Characteristics Associated with Vitamin D Deficiency in Sickle Cell and the Effect on Vitamin D Replacement. Blood. 2011;118(21):81-86.

28.

Brown

Long

Agdare

Kulpa

Zarzoso-Fernandez

Choudhary

Sundarum

. The association between vitamin D deficiency and hospitalization outcomes in pediatric patients with sickle cell disease. Blood Cells Mol Dis. 2020;82(102415).

29.

Busse

Seelaboyina

Malonga

, et al. Vitamin D Level and Its Correlation with Hemoglobin in Paediatric Sickle Cell Disease Patients. Blood. 2013;122:46-51.