Journal of Nutrition and Metabolism

Journal of Nutrition and Metabolism / 2021 / Article

Research Article | Open Access

Volume 2021 |Article ID 9987141 | https://doi.org/10.1155/2021/9987141

Samuel Asamoah Sakyi, Maxwell Hubert Antwi, Linda Ahenkorah Fondjo, Edwin Ferguson Laing, Richard K. Dadzie Ephraim, Alexander Kwarteng, Benjamin Amoani, Seth Christopher Appiah, Bright Oppong Afranie, Stephen Opoku, Tonnies Abeku Buckman, "Vitamin D Deficiency Is Common in Ghana despite Abundance of Sunlight: A Multicentre Comparative Cross-Sectional Study", Journal of Nutrition and Metabolism, vol. 2021, Article ID 9987141, 7 pages, 2021. https://doi.org/10.1155/2021/9987141

Vitamin D Deficiency Is Common in Ghana despite Abundance of Sunlight: A Multicentre Comparative Cross-Sectional Study

Academic Editor: Phillip B. Hylemon
Received21 Apr 2021
Revised26 May 2021
Accepted02 Jun 2021
Published11 Jun 2021

Abstract

Background. Vitamin D is a steroid hormone important for the normal functioning of the body. It is produced through skin exposure to sunlight and from the diet. Although Ghana is located in the tropics where sunlight is abundant, factors like culture, diet, skin pigmentation, variation in the ozone layer, and geographical area influence the optimization of vitamin D concentration. It is imperative to evaluate the interplay between sunshine exposure, proinflammatory cytokines, and mediators of vitamin D metabolism and their relationship to vitamin D status in three geographical sections among apparent healthy Ghanaians. Methods and Results. In a cross-sectional study, a total of five hundred (500) healthy blood donors from three geographical areas in Ghana were enrolled. Their age ranged from 17 to 55 years with a mean age of 27.97 ± 8.87 years. The overall prevalence rate of vitamin D deficiency was 43.6% (218/500), with 41.2% (91/221), 45.3% (63/139), and 45.7% (64/140) of vitamin D deficiency being recorded in participants from the Northern Sector (NS), Middle Belt (MB), and Southern Sector (SS), respectively. However, there were no significant differences in the proportions of vitamin D deficiency across various geographical sectors. The median 25-hydroxyvitamin D serum levels were compared among geographical areas (NS, MB, and SS) and there were no significant differences () after adjusting for confounding factors. 25-Hydroxyvitamin D correlated positively with corrected ionized calcium (rs = 0.622, ) and phosphorus (rs = 0.299, ) and negatively correlated with SBP (rs = −0.092, ), vitamin D binding protein (VDBP) (rs = −0.421, ), intact parathyroid hormone (iPTH) (rs = −0.0568, rs ≤ 0.001), IFN-gamma (rs = −0.684, ), and TNF-alpha (rs = −0.600, ). After adjusting for possible confounders, not having knowledge about vitamin D foods, taking fewer vitamin D foods, and higher levels of IF-γ and IL-10 were associated with a higher risk of having vitamin D deficiency. Conclusion. The prevalence of 25-hydroxyvitamin D deficiency is high among the general adult population in Ghana despite the abundance of sunlight. Increasing knowledge on vitamin D diet coupled with a daily intake of vitamin D dietary supplements is likely to reduce the risk of developing 25-hydroxyvitamin D deficiency.

1. Introduction

The “sunshine” vitamin, also called vitamin D, is a steroid hormone that is essential for the normal functioning of the body including the intestine, skin, bone, parathyroid glands, immune system, pancreas, and the healthy growth of a developing fetus [1]. 25-Hydroxyvitamin D deficiency has been identified as a global challenge in both healthy and unhealthy populations, and it is estimated that up to one billion healthy individuals are living with hypovitaminosis D globally [2]. Vitamin D produced from sunlight through skin exposure and from the diet is converted into 25-hydroxyvitamin D [25(OH)D] in the liver and is carried into the circulation by vitamin D binding protein to the kidney [1, 3, 4]. Vitamin D status is determined more by exposure of the skin to sunlight than by dietary intake of the vitamin, because food sources are relatively limited, particularly when the food supply is not fortified with vitamin D [5]. Vitamin D is one of the many nutrients our bodies need to stay healthy and is introduced to the body in two forms which are vitamin D3 and D2 [6]. Vitamin D3 is produced in the skin by ultraviolet B radiation (UVB) from sunlight and vitamin D2 is obtained in the diet from selected food sources, such as deep-sea fatty fish or egg yolk [7].

Vitamin D deficiency varies highly across regions, with the prevalence ranging between 30 and 90% [8]. A steady measure of getting vitamin D is endogenous skin synthesis through UVB light exposure at wavelengths of 290–315 nm [9] and it is estimated that sun exposure on bare skin for 5–10 minutes twice per week allows the body’s ability to produce sufficient vitamin D [10]. The kidney converts (25OHD) into the active form called 1, 25-dihydroxyvitamin D (1, 25(OH) 2D) through the activity of the enzyme 1-alpha hydroxylase (CYP27B1) whose function depends on parathyroid hormone (PTH), calcium, and phosphorous levels (33-34). It is thus important to assess the interplay between PTH, kidney function, calcium, and phosphorus levels amid adequate sunshine vis-a-vis vitamin D status. Tissues that are receptive to vitamin D express the vitamin D receptor gene (VDR) and 1-alpha hydroxylase (CYP27B1) enzymes and include many cells of the immune system (35).

The activity of the 1-alpha hydroxylase (CYP27B1) enzyme to produce local 1, 25(OH) 2D (calcitriol) in the immune environment depends on proinflammatory cytokines like TNF-alpha, IL6, and IFY (36–39).

Although Ghana is located in the tropics where sunlight is abundant, factors like culture (especially our style of dressing), diet, skin pigmentation, variation in the ozone layer, and geographical area (latitude) influence the optimization of vitamin D concentration [11, 12]. In addition, data on vitamin D status in sub-Saharan Africa is limited, especially in Ghana. It is thus imperative to evaluate the interplay between sunshine exposure, proinflammatory cytokines, and mediators of vitamin D metabolism and their relationship to vitamin D status in three geographical sections among apparent healthy Ghanaians.

2. Materials and Methods

2.1. Study Design/Settings

This cross-sectional study was conducted in selected hospitals across seven regions of Ghana for 5 months. The selected hospitals were (a) Bolgatanga Regional Hospital, Nandowli Hospital, and Kpandai Hospital, which present the Northern Sector (NS); (b) Wenchi Methodist Hospital and St. Patrick’s Hospital Offinso-Maase which present the Middle Belt (MB); (c), Effia Nkwanta Regional Hospital and Koforidua Regional Hospital which present the Southern Sector (SS) (Figure S1; Table S1). Ghana is geographically placed near the equator and lies between latitude: 7°57′9.97″N and longitude: −1°01′50.56″W. It occupies an area of about 240,000 km2 of the African continent and is the thirteenth most populated country in Africa and among the top five populated countries in West Africa, with more than 26 million people accounting for about 2.5% of African’s population (Ghana Statistical Service, 2010 Population and Housing Census) [13].

2.2. Questionnaire and Data Collection

Structured validated questionnaires were administered to study participants to obtain their sociodemographic characteristics, knowledge on vitamin D-rich foods, and frequent intake of various vitamin D-rich foods. Information on their health status about the presence or absence of chronic disease conditions was also included in the questionnaire.

2.3. Study Population/Subjects Selection

Using a systematic sampling technique, a total of five hundred (500) healthy blood donors between the ages of 17 years and 60 years were selected. A systematic random sampling technique was used for sample collection as described (Table S2). Healthy blood donors who have passed screening and are free from any diseases including pulmonary tuberculosis, diabetes mellitus, malaria, sexually transmitted infections (STIs), and blood-borne infections were included in this study. Pregnant women, children, subjects with clinical records or symptoms showing chronic ailments such as renal, hypertension, and any other diseases, and subjects with drugs that could influence vitamin D intake and metabolism were all excluded from the study.

2.4. Sample Collection Processing and Measurement

Ten (10) milliliters (ml) of venous blood was taken from a prominent vein of each donor. Three (3) ml of blood was dispensed into dipotassium ethylenediaminetetraacetic acid (K2EDTA) tubes, one (1) ml into fluoride oxalate tubes, and five (5) ml into gel separator tubes (5 ml MICRO POINT clot activator tube; batch number: KJ040AS). K2EDTA blood samples were screened for hemoglobin levels, typhoid test, hepatitis B and hepatitis C, HIV/AIDs, syphilis, and malaria. A calibrated copper solution of standard hemoglobin concentrations of 13.0 g/dl and 12.5 g/dl for males and females, respectively, was the method used to determine the hemoglobin level of the blood donors. The tubes were positioned in the centrifuge holes (HERMLE Z300K, Labsource, Inc., Romeoville, IL 60446) and spun at 3500 rpm for about 8 minutes to get plasma and serum where appropriate. Blood collected into fluoride oxalate tubes was screened for diabetes. The serum was aliquoted into cryotubes and stored at −70°C (Thermo Scientific™ Revco™ UxF—Ultra-Low Temperature Freezers, USA) until the measurement of the biochemical assays.

2.5. Biochemical Assays

The serum concentrations of 25(OH)D, intact parathyroid hormone (iPTH), and vitamin D binding protein (VDBP), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) were measured with Inqaba Biotec ELISA plate reader (Inqaba Biotechnical Industries (Pty) Ltd., South Africa) using reagents from Biobase Biotech (Jinan) Co., Ltd., China, whose basic principle is Sandwich enzyme-linked immunosorbent assay (ELISA). In addition, serum concentrations of ionized calcium, phosphorus, albumin, and creatinine were measured with the Biotechnica BT 3500 Chemistry analyzer using reagents from BT Biotechnica Co., Ltd., Rome, Italy.

2.6. Classification of 25(OH)D Status

Serum 25(OH)D levels less than 20 ng/ml were considered vitamin D deficient and those greater than 20 ng/ml as not deficient [14].

2.7. Calculation of Corrected Ionized Calcium

Corrected ionized calcium was then calculated using the following formula:

2.8. Statistical Analysis

IBM SPSS version 20.0 statistics was used to generate and analyze data and clean for outrageous values at regular intervals. Categorical variables were presented and reported as frequencies with their corresponding percentages. Means with their standard deviation and medians (ranges) were used to summarize continuous variables. Comparison between two means of parametric and nonparametric continuous variables was done using independent sample t-test and Mann–Whitney U test, respectively. Chi-square test statistic was employed to determine any association between the categorical variables. Spearman’s Rho statistic was used to determine the relationship between 25OHD and the biochemical parameters, while the odds of biochemical variables in predicting vitamin D deficiency were done using multivariate logistic regression analysis. A value of less than 0.05 was considered statistically significant. Coefficients were then determined with their respective 95% confidence intervals.

3. Results

A total of five hundred (500) healthy blood donors were enrolled in this study, of which 72.4% were males and 27.6% were females. Their ages ranged from 17 to 55 years with a mean age of 27.97 ± 8.87 years. The age group with the highest proportion was 20–29 years, contributing 47.8% of all participants. A total of 41.4% of the participants had secondary school education and the majority of the participants were still single (61.8%). Almost 75.2% of the study participants are Christians and 43.4% were informally employed (Table 1).


VariablesTotal (n = 500)Divisions value
NS (n = 221)MB (n = 139)SS (n = 140)

Age (years) (mean ± SD)27.97 ± 8.8727.19 ± 8.0526.31 ± 7.0230.83 ± 9.38<0.001

Age group (years)
 <2084 (16.8%)44 (52.4%)23 (27.4%)17 (20.2%)0.157
 20–29239 (47.8%)101 (42.3%)85 (35.5%)53 (22.2%)<0.001
 30–39121 (24.2%)58 (47.9%)17 (14.0%)46 (38.1%)<0.001
 ≥4056 (11.2%)18 (32.1%)14 (25.0%)24 (42.9%)0.027

Gender
 Male362 (72.4%)154 (42.5%)107 (29.6%)101 (27.9%)0.320
 Female138 (27.6%)67 (61.0%)32 (38.4%)39 (38.6%)0.320

Marital status
 Single309 (61.8%)138 (44.7%)101 (32.7%)70 (22.6%)<0.001
 Married180 (36.0%)80 (44.4%)36 (20.0%)64 (35.6%)0.003
 Divorced11 (2.2%)3 (27.3%)2 (18.2%)6 (54.5%)0.14

Religious status
 Christians376 (75.2%)167 (44.4%)105 (27.9%)104 (27.7%)0.957
 Muslims97 (19.4%)41 (42.3%)26 (26.8%)30 (30.9%)0.774
 Traditionalists27 (5.4%)13 (48.1%)8 (29.6%)6 (22.3%)0.475

Educational background
 None69 (13.8%)29 (42.0%)30 (43.5%)10 (14.5%)0.002
 Basic76 (15.2%)37 (48.7%)12 (15.8%)27 (35.3%)0.032
 Secondary207 (41.4%)95 (45.9%)38 (18.4%)74 (35.7%)<0.001
 Tertiary148 (29.6)60 (40.5%)59 (39.9%)29 (19.6%)<0.001

Occupational status
 Unemployed6 (1.2%)2 (33.3%)4 (66.7%)0.078
 Informal217 (43.4%)93 (42.9%)58 (26.7%)66 (30.4%)0.573
 Formal64 (12.8%)28 (43.8%)9 (14.1%)27 (42.2%)0.001
 Student213 (42.6%)98 (46.0%)72 (33.8%)43 (20.2%)0.342
 SBP (mmHg)114.64 ± 6.52114.34 ± 5.97115.54 ± 7.34114.21 ± 6.470.158
 DBP (mmHg)75.38 ± 5.3875.57 ± 5.1675.61 ± 5.6674.86 ± 5.430.398
 IPTH (pg/ml)7.12 (6.24–8.67)7.02 (5.95–8.77)7.30 (6.33–8.67)7.35 (6.38–8.62)0.409
 VDBP (ng/ml)26.38 (8.46–53.23)27.90 (8.38–61.67)21.57 (7.97–46.22)28.37 (9.90–28.77)0.035
 Corrected calcium (mmol/l)2.20 ± 0.192.20 ± 0.192.17 ± 0.172.21 ± 0.200.166
 Phosphorus (mmol/l)1.30 ± 0.171.31 ± 0.181.28 ± 0.131.32 ± 0.180.143
 Albumin (g/dl)43.09 ± 2.9043.27 ± 3.2242.86 ± 2.6243.04 ± 2.810.410
 Creatinine (mmol/l)99.52 ± 28.08101.34 ± 29.1894.92 ± 21.60101.22 ± 31.450.075

value <0.05 = statistically significant, SD = standard deviation, NS = Northern Sector, MB = Middle Belt, SS = Southern Sector, SBP = systolic blood pressure, DBP = diastolic blood pressure, IPTH = intact parathyroid hormone, and VDBP = vitamin D binding protein.

The median 25-hydroxyvitamin D serum levels were compared across geographical areas (NS, MB, and SS) and there were no significant differences () as confounding factors were adjusted (Figure 1(a)). The total prevalence rate of vitamin D deficiency was 43.6% (218/500) with 41.2% (91/221), 45.3% (63/139), and 45.7% (64/140) of vitamin D deficiency recorded for NS, MB, and SS, respectively (Figure 1(b)). However, there was no significant difference among the proportions of the prevalence of vitamin D deficiency among participants (NS vs. SS, ; NS vs. MB, ; SS vs. MB, ).

Serum 25-hydroxyvitamin D was correlated positively with corrected ionized calcium (r = 0.622, ) and phosphorus (r = 0.299, ) and negatively correlated with SBP (r = −0.092, ), VDBP (r = −0.421, ), IPTH (r = −0.568, ), IFN-gamma (r = −0.684, ), IL-10 (r = 0.575, ), and TNF-alpha (r = −0.600, ). Results are shown in Table 2.


Vitamin D 25(OH)D (ng/ml)
Pearson correlation (r) valueN

VDBP (ng/ml)−0.421<0.001500
(IPTH) (pg/ml)−0.568<0.001500
Corrected ionized calcium (mmol/l)0.622<0.001500
Phosphorous (mmol/l)0.1990.102500
Albumin (g/dl)0.1100.114500
Creatinine (mmol/l)0.0570.205500
IL 10 (pg/ml)0.575<0.001500
TNF-alpha (pg/ml)−0.300<0.001500
IFN-gamma (pg/ml)−0.356<0.001500
Body weight (kg)−0.0120.786500
DBP (mm/Hg)0.0370.414500
SBP (mm/Hg)−0.0920.039500
Age0.0430.337500

value <0.05 = statistically significant, SBP = systolic blood pressure, DBP = diastolic blood pressure, IPTH = intact parathyroid hormone, VDBP = vitamin D binding protein, IL-10 = interleukin-10, TNF-alpha = tumor necrosis factor-alpha, and IFN-gamma = interferon-gamma.

Table 3 depicts the binary logistic regression analysis which predicted the odds ratio for risk factors of vitamin D deficiency among study participants. For both the crude and adjusted odds ratio, participants who did not know vitamin D foods were at a higher risk of having vitamin D deficiency (cOR = 2.93, ; aOR = 4.39, ). With the adjusted odds ratio, those who take in milk weekly have a higher chance of having vitamin D deficiency (aOR = 2.63, ). In addition, eating salmon monthly as compared to the rest makes the participants at higher risk of vitamin D deficiency (aOR = 1.96, ). Furthermore, those who only monthly take in fruits and vegetables are highly vulnerable to having vitamin deficiency status (aOR = 7.02, ); see Tables 3 and S3.


VariablesFrequency (n = 500)Univariate (95% CI) valueMultivariate (95% CI) value

Knowledge of vit D foods
 Yes32ReferentReferent
 No4682.93 (0.15–0.80)0.0144.39 (1.69–11.44)0.002

Milk intake
 Not taken68ReferentReferent
 Daily310.49 (0.28–0.84)0.0091.77 (0.92–3.14)0.088
 Weekly1520.94 (0.41–2.22)0.8242.63 (1.05–6.59)0.040
 Monthly2490.95 (0.41–2.22)0.9022.11 (1.29–3.47)0.003

Salmon (oily fish)
 Not taken
 Daily185ReferentReferent
 Weekly2212.08 (1.38–3.12)<0.0011.78 (1.09–2.90)0.022
 Monthly942.43 (1.46–4.04)0.0011.96 (1.06–3.64)0.032

Fruit/vegetable intake
 Not taken
 Daily50ReferentReferent
 Weekly2542.12 (1.01–4.44)0.0462.45 (1.10–5.43)0.028
 Monthly1966.32 (2.98–13.37)<0.0017.02 (3.08–16.05)<0.001

Interleukin-10
 Normal (<10 pg/mL)419ReferentReferent
 High (≥10 pg/mL)813.47 (1.97–6.13)<0.0013.15 (1.65–6.01)<0.001

Interferon-gamma
 Normal (<8 pg/mL)155ReferentReferent
 High (≥8 pg/mL)34513.10 (8.53–20.12)0.00110.77 (6.08–19.06)<0.001

value <0.05 = statistically significant; vit D = vitamin D; for multivariate analysis all other factors such as hemodynamics, biochemistry parameters, age, and weight were adjusted.

4. Discussion

Ghana is a tropical country with a lot of sunlight; however, it is not a homogenous entity for geography, climate, water sources, food production and availability, or the religious and cultural practices, skin pigmentation, and burden of infectious and chronic diseases of its people. All these factors are likely to affect and/or be affected by vitamin D status [15]. We, therefore, investigated whether the abundance and variability of sunlight in Ghana necessarily confer adequate vitamin D optimization among apparent healthy Ghanaians in three geographical sections. We also explored the factors associated with vitamin D deficiency.

The results of the study confirm a high prevalence of vitamin D deficiency of 43.6% among the adult healthy population in Ghana. In a cross-sectional study among the healthy adult population of Isfahan in Iran, vitamin D deficiency (25OHD <20 ng/mL) was observed to be 50.8% which is higher than this current study. Although Isfahan is a sunny city, direct exposure to the sun is, however, limited because in most Muslim countries, all women are required to wear a scarf (Hajib) and long-sleeve clothes and they constituted 78.1% of their study participants. This why Iran has more severe vitamin D deficiency than Ghana which is mostly a Christian country [16, 17], even though Iran and Ghana are located in the subtropics (dry hot) and tropics (humid hot), respectively [18].

In this study, 41.2% (91/221), 45.3% (63/139), and 45.7% (64/140) of vitamin D deficiency rates were recorded for the Northern Sector (NS), Middle Belt (MB), and Southern Sector (SS) of Ghana, respectively, with no significant proportional differences even though there are variations in the latitudes and intensity of sunshine in these areas [13]. A cross-sectional study among the healthy seminomadic Fulani population in northern part of Nigeria by Glew et al. reported a vitamin D deficiency of 21.6%, which is lower than the rate observed in this current study for NS since both geographical areas have similar “high sunshine.” The observed difference could partly be explained by the fact that most of their study populations were cattle farmers tending to their cattle, thereby benefitting from extensive exposure of their skin to sunlight [19]. However, the majority of the NS participants in the current study were students or formally employed which kept them indoors. Consequently, it is not solely the abundance of sunshine that influences the optimization of vitamin D concentrations but rather the exposure of the skin to the ultraviolet ray of the sunlight [20]. Results from this study are inconsistent with a study by Gebreegziabher and Stoecker as they reported that about 84.2% of people situated in the southern part of Ethiopia were vitamin D deficient [21].

It was significantly observed in this study that most of the participants from the southern sector take dairy products frequently compared to participants from other geographical areas. Apart from this, there were equal proportions of frequencies recorded for the predisposing risk factors stratified among the three geographical areas [additional file, Table S2]. Results from this study show that intake of various vitamin D-rich foods independently gives one less chance of being vitamin D deficient. Moreover, consistently with previous studies, not knowing vitamin D foods [22], taking fewer vitamin D foods [23, 24], and higher levels of IF-γ and IL-10 [25] were associated with higher chances of having vitamin D deficiency.

From the correlation analysis, the results were similar to other studies as 25-hydroxyvitamin D was correlated positively with corrected ionized calcium and phosphorus [26] and negatively correlated to systolic blood pressure [27, 28], vitamin D binding protein, parathyroid hormone (PTH) [29, 30], interferon-gamma, and tumor necrosis factor-alpha [31].

In this study, therefore, the vitamin D deficiency determinants were controlled when comparing the serum levels of 25-hydroxyvitamin D across the geographical areas. In this comparative cross-sectional study, substantial variability in serum 25(OH)D concentrations does not exist despite the varying degree of abundant sun exposure, as median serum 25(OH)D levels of participants were significantly equal across geographical sections of Ghana (NS, MB, and SS). The limitation of the current study is our inability to measure the sun exposure habits of the respondents. However, this has no substantive effect on our main findings.

5. Conclusion

The prevalence of 25(OH)D deficiency is high among the general adult population in all three sectors of Ghana despite the abundance and variability in sunlight. Increased level skin exposure to sunlight coupled with a daily intake of vitamin D dietary supplements will reduce the risk of developing 25(OH)D deficiency.

Data Availability

The datasets supporting the conclusions of this article are included within the article and its additional file.

Ethical Approval

Ethical approval for this study was obtained from the Committee on Human Research, Publication and Ethics (CHRPE) at the School of Medical Sciences, Kwame Nkrumah University of Science and Technology (CHPRE/AP/237/16), and the Institutional review board of the various hospitals involved.

Participation was voluntary and written informed consent was obtained from each participant according to the Helsinki declaration [32].

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Supplementary Materials

Figure S1: flowchart of the protocol for the selection of subject. Table S1: geographical study sites and their respective coordinates. Table S2: sampling technique method. Table S3: association between predisposing factors for vitamin D deficiency and the stratified geographical areas. Table S4: binary logistic regression analysis predicting the odds ratio for sociodemographics with respect to vitamin D deficiency among study participants. (Supplementary Materials)

References

  1. H. Nimitphong and M. F. Holick, “Vitamin D status and sun exposure in southeast Asia,” Dermato-Endocrinology, vol. 5, no. 1, pp. 34–37, 2013. View at: Publisher Site | Google Scholar
  2. F. T. E. Christie and L. Mason, “Knowledge, attitude and practice regarding vitamin D deficiency among female students in Saudi Arabia: a qualitative exploration,” International Journal of Rheumatic Diseases, vol. 14, no. 3, pp. e22–e29, 2011. View at: Publisher Site | Google Scholar
  3. M. Holick, “Vitamin D: photobiology, metabolism of action, and clinical applications,” Primer on the Metabolic Bone Diseases, Lippincott Williams and Wilkins, Philadelphia, PA, USA, 1999. View at: Google Scholar
  4. M. Natasja and P. Lips, “Worldwide vitamin D status,” Best Practice & Research Clinical Endocrinology & Metabolism, vol. 25, pp. 671–680, 2011. View at: Google Scholar
  5. F. Libon, E. Cavalier, and A. F. Nikkels, “Skin color is relevant to vitamin D synthesis,” Dermatology, vol. 227, no. 3, pp. 250–254, 2013. View at: Publisher Site | Google Scholar
  6. A. Ascherio, K. L. Munger, and K. C. Simon, “Vitamin D and multiple sclerosis,” The Lancet Neurology, vol. 9, no. 6, pp. 599–612, 2010. View at: Publisher Site | Google Scholar
  7. T. D. Thacher and B. L. Clarke, “Vitamin D insufficiency,” Mayo Clinic Proceedings, Elsevier, Amsterdam, Netherlands, 2011. View at: Google Scholar
  8. I. M. Van der Meer, B. J. C. Middelkoop, A. J. P. Boeke, and P. Lips, “Prevalence of vitamin D deficiency among Turkish, Moroccan, Indian and sub-Sahara African populations in Europe and their countries of origin: an overview,” Osteoporosis International, vol. 22, no. 4, pp. 1009–1021, 2011. View at: Publisher Site | Google Scholar
  9. M. Wacker and M. F. Holick, “Sunlight and vitamin D: a global perspective for health,” Dermato-Endocrinology, vol. 5, no. 1, pp. 51–108, 2013. View at: Publisher Site | Google Scholar
  10. M. F. Holick, “Vitamin D deficiency,” New England Journal of Medicine, vol. 357, no. 3, pp. 266–281, 2007. View at: Publisher Site | Google Scholar
  11. L. A. Fondjo, W. K. B. A. Owiredu, S. A. Sakyi et al., “Vitamin D status and its association with insulin resistance among type 2 diabetics: a case -control study in Ghana,” PLoS One, vol. 12, no. 4, Article ID e0175388, 2017. View at: Publisher Site | Google Scholar
  12. S. Afzal, S. E. Bojesen, and B. G. Nordestgaard, “Low 25-hydroxyvitamin D and risk of type 2 diabetes: a prospective cohort study and metaanalysis,” Clinical Chemistry, vol. 59, no. 2, pp. 381–391, 2013. View at: Publisher Site | Google Scholar
  13. S. N. A. Codjoe, “Integrating remote sensing, GIS, census, and socioeconomic data in studying the population-land use/cover nexus in Ghana: a literature update,” Africa Development, vol. 32, no. 2, 2007. View at: Google Scholar
  14. L. A. Fondjo, S. A. Sakyi, W. K. B. A. Owiredu et al., “Evaluating vitamin D status in pre- and postmenopausal type 2 diabetics and its association with glucose homeostasis,” BioMed Research International, vol. 2018, Article ID 9369282, 12 pages, 2018. View at: Publisher Site | Google Scholar
  15. A. Prentice, I. Schoenmakers, K. S. Jones, L. M. A. Jarjou, and G. R. Goldberg, “Vitamin D deficiency and its health consequences in Africa,” Vitamin D, Springer, Berlin, Germany, 2010. View at: Publisher Site | Google Scholar
  16. S. Hovsepian, M. Amini, A. Aminorroaya, P. Amini, and B. Iraj, “Prevalence of vitamin D deficiency among adult population of Isfahan city, Iran,” Journal of Health, Population, and Nutrition, vol. 29, no. 2, p. 149, 2011. View at: Publisher Site | Google Scholar
  17. A. Langer, “Living with diversity: the peaceful management of horizontal inequalities in Ghana,” Journal of International Development, vol. 21, no. 4, pp. 534–546, 2009. View at: Publisher Site | Google Scholar
  18. A. Erez, “Bud dormancy; phenomenon, problems and solutions in the tropics and subtropics,” Temperate Fruit Crops in Warm Climates, Springer, Berlin, Germany, 2000. View at: Publisher Site | Google Scholar
  19. R. H. Glew, M. J. Crossey, J. Polanams, H. I. Okolie, and D. J. VanderJagt, “Vitamin D status of seminomadic Fulani men and women,” Journal of the National Medical Association, vol. 102, no. 6, pp. 485–490, 2010. View at: Publisher Site | Google Scholar
  20. N. Binkley, R. Novotny, D. Krueger et al., “Low vitamin D status despite abundant sun exposure,” The Journal of Clinical Endocrinology & Metabolism, vol. 92, no. 6, pp. 2130–2135, 2007. View at: Publisher Site | Google Scholar
  21. T. Gebreegziabher and B. Stoecker, “Vitamin D insufficiency in a sunshine-sufficient area: southern Ethiopia,” European Journal of Nutrition & Food Safety, vol. 5, no. 5, p. 920, 2015. View at: Publisher Site | Google Scholar
  22. D. Malaeb, S. Hallit, and P. Salameh, “Assessment of vitamin D levels, awareness among Lebanese pharmacy students, and impact of pharmacist counseling,” Journal of Epidemiology and Global Health, vol. 7, no. 1, pp. 55–62, 2017. View at: Publisher Site | Google Scholar
  23. T. Jääskeläinen, S. T. Itkonen, A. Lundqvist et al., “The positive impact of general vitamin D food fortification policy on vitamin D status in a representative adult Finnish population: evidence from an 11-y follow-up based on standardized 25-hydroxyvitamin D data,” The American Journal of Clinical Nutrition, vol. 105, no. 6, pp. 1512–1520, 2017. View at: Publisher Site | Google Scholar
  24. A. Hayes and K. D. Cashman, “Food-based solutions for vitamin D deficiency: putting policy into practice and the key role for research,” Proceedings of the Nutrition Society, vol. 76, no. 1, pp. 54–63, 2017. View at: Publisher Site | Google Scholar
  25. D. Ragab, D. Soliman, D. Samaha, and A. Yassin, “Vitamin D status and its modulatory effect on interferon gamma and interleukin-10 production by peripheral blood mononuclear cells in culture,” Cytokine, vol. 85, pp. 5–10, 2016. View at: Publisher Site | Google Scholar
  26. M. R. Clements, L. Johnson, and D. R. Fraser, “A new mechanism for induced vitamin D deficiency in calcium deprivation,” Nature, vol. 325, no. 6099, pp. 62–65, 1987. View at: Publisher Site | Google Scholar
  27. S. K. Kunutsor, S. Burgess, P. B. Munroe, and H. Khan, Vitamin D and High Blood Pressure: Causal Association or Epiphenomenon? Springer, Berlin, Germany, 2014.
  28. H. Tamez, S. Kalim, and R. I. Thadhani, “Does vitamin D modulate blood pressure?” Current Opinion in Nephrology and Hypertension, vol. 22, no. 2, pp. 204–209, 2013. View at: Publisher Site | Google Scholar
  29. S. J. Weintraub, “Vitamin D-binding protein and vitamin D in blacks and whites,” New England Journal of Medicine, vol. 370, no. 9, pp. 878–881, 2014. View at: Publisher Site | Google Scholar
  30. T. Naveh-Many and J. Silver, “Regulation of parathyroid hormone gene expression by hypocalcemia, hypercalcemia, and vitamin D in the rat,” Journal of Clinical Investigation, vol. 86, no. 4, pp. 1313–1319, 1990. View at: Publisher Site | Google Scholar
  31. M. Fabri, S. Stenger, D.-M. Shin et al., “Vitamin D is required for IFN-γ-mediated antimicrobial activity of human macrophages,” Science Translational Medicine, vol. 3, no. 104, Article ID 104ra2, 2011. View at: Publisher Site | Google Scholar
  32. Association GAotWM, “World Medical Association declaration of Helsinki: ethical principles for medical research involving human subjects,” The Journal of the American College of Dentists, vol. 81, no. 3, p. 14, 2014. View at: Google Scholar

Copyright © 2021 Samuel Asamoah Sakyi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Related articles

No related content is available yet for this article.
 PDF Download Citation Citation
 Download other formatsMore
 Order printed copiesOrder
Views1490
Downloads729
Citations

Related articles

No related content is available yet for this article.

Article of the Year Award: Outstanding research contributions of 2021, as selected by our Chief Editors. Read the winning articles.