Correlation Between Vitamin D Level and Bone Mineral Density in Kenyan Adults Aged 50 Years and Above at Kenyatta National Hospital

Abstract

Background: There is inconsistent evidence in the orthopedic literature on presence of a correlation between vitamin D levels and reduced bone mineral density (BMD) and the relationship is sometimes controversial. Nine percent of Kenya’s population is at least 50 years and above. Quantitative ultrasound (QUS) is an appropriate tool for determining BMD profile. Main Objective: To evaluate the correlation between serum 25-hydroxyvitamin D (25(OH)D) levels and BMD. Methodology: A cross-sectional study was conducted on 126 patients in Kenyatta national Hospital (KNH). Calcaneal QUS was used to measure BMD. The participants were asked to remove their shoes and stand on one foot on the ultrasound machine. Two measurements were conducted on both feet for all study participants. Descriptive data were presented as proportions and means with their standard deviations (SD) appropriately. Fisher’s exact Test or Chi-square Test were used in comparison of categorical variables while Mann-Whitney test or Kruskal-Wallis Anova were used in comparing serum vitamin D levels (continuous variable) in the age categories appropriately. Point biserial correlation coefficient test was used to assess the correlation between vitamin D and BMD. Stepwise linear and stepwise logistic regression were used to adjust for confounders. Results: The patients’ mean age was 61.31± SD of 8.18. Of the 126 patients, 64.3% were males, and 63.7% had a history of bone fracture. The proportion of reduced BMD was 87.3% while 12.7% normal. Vitamin D deficient (<20 ng/mL), insufficient (20–29 ng/mL) and normal (≥ 30 ng/mL) were 10.3%, 31.7% and 57.9%, respectively. There was no evidence that serum vitamin D correlated differently in orthopedic outpatients and inpatients with BMD (p-value = 0.189). A statistically significant weak positive bivariate correlation of 0.351 was found between serum vitamin D and BMD. Serum vitamin D was associated/correlated with reduced BMD [adjusted OR: 1.16, 95% confidence interval (CI): 1.08 – 1.25; p-value <0.001] compared to normal BMD in adjusted logistic model. In an adjusted linear regression model, patients with reduced BMD had 7.53 (95% CI: 1.29–13.76; p-value =0.018) higher serum vitamin D levels than normal BMD. Patients in age category 70 – 79 years disproportionately had reduced BMD than other age categories. The proportions of reduced BMD were statistically significantly different across the age groups (p-value = 0.029)..........................................................................................