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| ORIGINAL ARTICLE |
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| Year : 2022 | Volume
: 12
| Issue : 1 | Page : 15-20 |
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Vitamin D status and bone health in healthy adult Nigerians
Ayotunde Oladunni Ale1, Sanya Bamidele Osalusi1, Olusola L Adeyemo2
1 Department of Medicine, Obafemi Awolowo College of Health Sciences, Olabisi Onabanjo University Teaching Hospital, Sagamu, Ogun State, Nigeria
2 Obafemi Awolowo College of Health Science, Olabisi Onabanjo University, Agoiwoye, Ogun State, Nigeria
| Date of Submission | 24-Jun-2021 |
| Date of Acceptance | 07-Sep-2021 |
| Date of Web Publication | 02-Sep-2022 |
Correspondence Address:
Dr. Ayotunde Oladunni Ale
Department of Medicine, Obafemi Awolowo College of Health Sciences, Olabisi Onabanjo University Teaching Hospital, Sagamu, Ogun State
Nigeria
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/ajem.ajem_7_21
Background: With the emergence of osteoporosis as a major public health concern among economically developed nations, more research is needed on the prevalence and etiology of this and related diseases in resource-limited countries. This study evaluated vitamin D status and its relationship with skeletal health in healthy adult Nigerians. Materials and Methods: Forty apparently healthy subjects between the ages of 21 and 50 were recruited in this prospective study. A variety of physiological parameters were assessed including markers of bone health, thyroid function, and renal function, as well as parathyroid hormone levels, calcium excretion rates, and serum 25-hydroxyvitamin-D levels. Bone mineral density (BMD) was evaluated via dual-energy X-ray absorptiometry. Results: Mean serum 25-hydroxyvitamin-D level was 53 (15.66) nmol/L and 70% of the subjects had vitamin D insufficiency. Osteopenia was observed in 25% of the subjects, and none of the subjects presented with osteoporosis. The BMD T-score of subjects with osteopenia was significantly lower when compared with non-osteopenic subjects. Serum osteocalcin was significantly higher in osteopenic subjects when compared with non-osteopenic subjects, but 24-h calcium excretion was comparable between the two groups. Mean serum 25-hydroxyvitamin-D in subjects with osteopenia was lower when compared with non-osteopenic subjects, whereas thyroid, renal, and calcium-phosphorus parameters were not significantly different between the groups. Conclusion: There is a high rate of vitamin D insufficiency and bone loss among apparently healthy Nigerians, and we propose vitamin D status and bone health as targets for intervention. Keywords: Bone mineral density, healthy Nigerians, steopenia, vitamin D status
How to cite this article:
Ale AO, Osalusi SB, Adeyemo OL. Vitamin D status and bone health in healthy adult Nigerians. Afr J Endocrinol Metab 2022;12:15-20 |
| Introduction | |  |
Osteoporosis and related diseases have emerged as a major public health concern worldwide. Among the countries of the European Union, the economic burden of osteoporosis-related fractures has been estimated at a staggering €37 billion.[1] In the United States alone, there are an estimated 54 million people affected, with approximately 2 million osteoporosis-related fractures occurring annually at a cost upwards of $17 million per year.[2],[3] Less is known about the prevalence and socioeconomic impact of this disease in lower- and middle-income countries (LMICs), like Nigeria, where the healthcare systems have limited resources and many competing priorities. The major focus of the healthcare systems has been on the communicable diseases.[4],[5] In particular, obtaining high-quality measurements of bone mineral density (BMD), a key indicator of bone health, requires the use of dual-energy X-ray absorptiometry (DXA), an advanced and expensive device that is not readily available among healthcare providers of LMICs.[4]
The role of vitamin D in promoting bone health is well documented.[6],[7] The classical endocrine function of vitamin D is to regulate calcium homeostasis and to maintain skeletal integrity by facilitating intestinal calcium absorption and preventing secondary hyperparathyroidism. Vitamin D status is assessed clinically by measuring serum 25-hydroxyvitamin-D concentrations.[8],[9] Several epidemiological studies have reported lower serum 25-hydroxyvitamin-D levels to be associated with increased parathyroid hormone (PTH) secretion, decreased BMD, and increased fracture risk.[10],[11],[12],[13],[14],[15]
Risk of vitamin D deficiency or insufficiency is influenced by a complex set of factors including age, dermal pigmentation, and diet.[16],[17] As a result, the incidence of vitamin D deficiency/insufficiency, and consequently the rate of osteoporosis and bone-related diseases, can be expected to vary based on the demographic characteristics of the population under study.
This exploratory and pilot study is the first of its kind to investigate bone health and its relationship to vitamin D levels in apparently healthy adult Nigerians. Based on similar studies in other population groups, low serum vitamin D is expected to coincide with signs of disrupted calcium homeostasis, specifically greater bone turnover, higher levels of PTH, and decreased BMD. This research has important implications for understanding the true scope of the socioeconomic burden of osteoporosis and related diseases in LMICs like Nigeria and for the viability of vitamin D status as a target to mitigate that burden.
| Materials and methods | | |
Subjects
The study included 40 healthy Nigerians in the age group of 21–50 years. They were selected by systemic random sampling and were controls of a hyperthyroid bone study. This study was approved by the Research and Ethical Committee of Lagos State University Teaching Hospital, Ikeja Lagos State. All participants gave informed consent before the commencement of the study.
Subjects with chronic medical disorders, a family history of fractures or history of multiple fractures since childhood, proteinuria, a history of alcohol consumption (24 g per day or greater), a history of smoking (20 pack-years or greater), high caffeine intake, and subjects who used estrogens, thiazide diuretics, or calcium for the management of osteoporosis and vitamin D in the last 12 months, as well as pregnant women and menopausal women were excluded from the study.
Clinical assessment
Clinical data were obtained using an interviewer-administered questionnaire by specialized physicians. Weight was recorded to the nearest 0.5 kg, and height was measured with a stadiometer and recorded to nearest 0.1 cm. Body mass index (BMI) was calculated as weight/height2. Waist circumference was measured using a metric non-stretching measuring tape, midway between the inferior margin of the lowest rib and the iliac crest in the horizontal plane, at the end of normal expiration. Blood pressure was measured.
Sample collection
Five milliliters of fasting venous blood was collected under sterile conditions for clinical chemistry and hormone analyses. Three milliliters of blood was centrifuged and the sera were separated the same day and distributed in aliquots. The aliquots were stored at −20°C until used. Two milliliters of blood was collected into heparin-lithium bottles for the determination of serum calcium, phosphorus, creatinine, and alkaline phosphatase.
The early morning urine sample was also collected in the fasting state and used for the assessment of calcium, phosphorus, and creatinine.
Laboratory assessment
Quantitative assay of osteocalcin, serum 25-hydroxyvitamin-D, and thyroid function tests (TSH, FT4, and FT3) were performed in Immunoassay Laboratories, the pioneer laboratories for enzyme-linked immunosorbent assay (ELISA) in Nigeria. The PTH assay was carried out in Mecure Diagnostic Laboratory in Nigeria.
Biochemical analysis
Serum calcium was determined by the timed-endpoint method[18]; the serum albumin measurement was based on BCG (Bromocresol Green) albumin assay method[19]; inorganic phosphorus was determined using molybdate method[20]; alkaline phosphatase was determined using the method of Hausamen et al.[21]; and creatinine by the modified Jaffe method.[22]
Hormonal analysis
Quantitative determination of serum osteocalcin, 25-hydroxyvitamin-D, TSH, FT4, and FT3 were performed using the ELISA method, whereas PTH was determined by the electrochemiluminescence immunoassay technique.
Bone densitometry
All the recruited subjects were evaluated for BMD. Clinical evaluation of BMD was performed using DXA Lunar PIXI #50734 at First Diagnostic Centre, Ikeja, Lagos, Nigeria.
Operational definitions
- Vitamin D deficiency was defined as serum 25-hydroxyvitamin-D concentration of <25 nmol/L, vitamin D insufficiency as 25–50 nmol/L, and normal vitamin D as >50nmol/L.[8]
- Increased bone turnover was present if serum osteocalcin was >25.3 ng/mL and/or 24-h calcium excretion was >4 mg/kg.
- Osteoporosis scores were defined as per WHO criteria, where a T-score of <−2.5 is osteoporotic, a T-score of −1 to −2.5 is osteopenic, and a T-score >−1 is normal.[23]
Statistical analysis
Data analysis was performed using the Statistical Package for Social Sciences (SPSS for Windows, version 21.0, SPSS Institute, Chicago, IL, USA). Quantitative (continuous) data were expressed as mean and standard deviation (SD), whereas qualitative (categorical) data were reported as percentages. A Levene’s test for homogeneity was used to evaluate the distribution of the data. Student’s t-test was used to compare quantitative data, whereas the χ2 test was used to compare qualitative data between different groups. Pearson’s correlation coefficient was used to determine the extent of the relationship between the tested variables. P-values less than 0.05 were considered significant.
| Results | | |
Characteristics of the study population
The mean age of the subjects was 34.10 (7.88) years. Among the study subjects, 65% were females and 35% were males. Mean BMI, waist circumference, systolic blood pressure, diastolic blood pressure, and fasting blood sugar were 26.32 kg/m2 (4.07), 78.60 cm (17.07), 112.4 mmHg (13), 76 mmHg (7.09), and 84.9 mg/dL (12.6), respectively.
Vitamin D status and BMD T-scores of participants
The mean vitamin D level of the subjects was 53.6 (15.66) nmol/L. Vitamin D insufficiency was recorded in 70% of the study subjects. Among the vitamin D-insufficient subjects, 35.71% were male and 64.29% were female. Vitamin D deficiency was not recorded in any of the study subjects. Serum vitamin D had no correlation with BMI, waist circumference, or blood pressure but did correlate to urinary calcium and phosphorus [Table 1]. | Table 1: Correlation between serum 25-hydroxyvitamin-D concentration (nmol/L) and other physiological variables
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DXA analysis revealed that 25% of the study subjects exhibited bone density scores consistent with osteopenia, whereas 0% had osteoporosis.
Characteristics of osteopenic subjects
Mean age and BMI of subjects were not significantly different between subjects who were osteopenic-positive and osteopenic-negative. However, the mean waist circumference was significantly lower and systolic blood pressure was significantly higher in osteopenic-positive subjects when compared with osteopenic-negative subjects [Table 2]. | Table 2: Comparison of clinical parameters between osteopenic-negative and osteopenic-positive subjects
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Serum osteocalcin was significantly higher in osteopenic-positive subjects, whereas 24-h calcium excretion levels were comparable between the two groups [Table 3]. | Table 3: Comparison of physiological parameters between osteopenic-negative and osteopenic-positive subjects
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Osteopenic-positive subjects had significantly lower serum vitamin D compared with osteopenic-negative subjects [Table 3].
Correlation analysis showed that PTH and osteocalcin correlated negatively with BMD T-scores. There were no associations between BMD T-score and other clinical and biochemical parameters [Table 4]. | Table 4: Correlation between BMD T-score and other physiological parameters
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| Discussion | | |
A proportion of subjects that exhibited vitamin D insufficiency was 70%, a rate comparable to populations in Asia and Middle-Eastern regions.[24] The low rate of vitamin D deficiency was comparable to findings in healthy adults from Latin America and the Caribbean[25] and Europe,[16] whereas studies in Asia and Middle-Eastern regions found substantially higher rates of vitamin D deficiency.[24] In the present study, it was observed that vitamin D insufficiency was independent of gender, with both males and females experiencing vitamin D insufficiency at a similar rate, in contrast to other studies which have reported females to have significantly lower serum vitamin D.[26] This conclusion on gender in this study is difficult to make because of the small sample size of the study population and the fact that they were not sex-matched: the females far outnumbered the males.
Previous studies that examined healthy Nigerian women via calcaneus ultrasound found 24% of the women to be osteopenic, a similar rate was found in the present study.[27] Given that the female sex has been shown to be disproportionately affected by osteoporosis and related diseases, it would be reasonable to expect that a mixed-sex subject group would have a lower rate of osteopenia than a female-only subject group. It is possible that the use of DXA analysis in this study enabled a greater degree of sensitivity in detecting osteopenia, compensating for the effect of sex, but further analysis that controls for sex is required to test this hypothesis. Another study of adult Nigerians assessing primary health care reported an osteoporosis rate of 29.2% and osteopenia rate of 38%, substantially higher than what was observed in this study.[28] These differences may be a reflection of the specific population that consisted of adults sampled from the primary healthcare system rather than from the general population.
Vitamin D levels in the subjects were not significantly correlated with PTH levels, serum osteocalcin, or BMD T-scores, as was predicted, but did exhibit a significant inverse correlation to calcium excretion, one of the parameters suggestive of bone loss. Conversely, BMD T-scores did exhibit a significant correlation to PTH levels and serum osteocalcin. To add to the complexity of the findings, subjects whose T-scores were osteopenic had significantly lower serum vitamin D and significantly higher serum osteocalcin than those who had normal T-scores, but both groups exhibited comparable levels of calcium excretion. The absence of a correlation between BMD T-scores and calcium excretion rate was also observed in a study of osteoporotic patients by El-Husseini et al.[29] PTH was not significantly different between the two groups, but this finding may be a feature of the limited power of this study. Collectively, these findings may suggest that PTH and serum osteocalcin are more advanced indicators of bone loss that are only elevated beyond a specific bone loss threshold. Conversely, low serum vitamin D may serve as one of the earliest signs of disrupted calcium homeostasis and therefore may serve as an ideal target for preventing future bone deterioration. The existence of a correlation between calcium excretion and serum vitamin D, but the absence of a significant difference in urinary calcium levels between osteopenic and non-osteopenic subjects, may suggest the presence of non-linear relationship between these parameters and potentially the existence of a negative feedback loop activated in healthy adults with lower bone density in order to limit further loss of calcium via excretion.
Limitation
As a preliminary study, the sample size and the corresponding statistical power were limited. A greater sample size would be beneficial to confirm the relationship between PTH levels and BMD in adult Nigerians, as well as further explore the effect of gender on vitamin D status.
We recommend that future research should incorporate subjects that are vitamin D-deficient and/or osteoporotic in order to broaden the scope of understanding of the relationship between vitamin D status and bone health.
| Conclusion | | |
Despite its small sample size, the socioeconomic implications of this study are dire. With a high proportion of healthy adults presenting with osteopenia, and a large majority exhibiting vitamin D insufficiency and some indicators of bone degradation, osteoporosis and related bone diseases are primed to reach epidemic levels in Nigeria barring active intervention.
Therefore, we recommend the public promotion of increased vitamin D intake via consumption of vitamin D-rich or -fortified foods, the use of vitamin D supplements, and safe levels of UVB exposure. We also advise routine screening to prevent further deterioration or progression of osteoporosis in order to reduce the burden of fractures in the near future.
Finally, low bone density is common among healthy Nigerians and linked with reduced vitamin D levels. Vitamin D status is a viable target for public health intervention and mitigation of socioeconomic impact of osteoporosis and related diseases.
Acknowledgment
The immense contribution of Dr Akintunde Ujomoti in review of this paper is highly appreciated.
Financial support and sponsorship
The authors disclosed no funding related to this article.
Conflicts of interest
The authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.
Author contributions
Concept/design: AOA. Definition of intellectual content: AOA. Literature: AOA, OBS, OLA. Clinical studies/experimental studies: AOA. Data acquisition/analysis and statistical analysis: AOA, OBS, OLA. Manuscript preparation: AOA, OBS. Manuscript editing and review: AOA, OBS, OLA. Manuscript approval: AOA, OBS, OLA.
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[Table 1], [Table 2], [Table 3], [Table 4]
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