Vitamin D Levels in Black African Adults at the Aga Khan University Hospital Nairobi
Date of Award
Master of Medicine (MMed)
Prof. Peter J. Ojwang
Dr. Nancy Okinda
Dr. Geofrey Omuse
Pathology (East Africa)
Introduction: Vitamin D has been known for centuries for its benefits in bone health. Recent observational studies have however demonstrated its benefits in infectious diseases such as tuberculosis and non-communicable diseases such as diabetes mellitus, cardiovascular diseases and cancer. This has led to a dramatic increase in testing among adults. The cut-offs for vitamin D deficiency have been debated for decades and the current cut off is derived from a Caucasian population. Studies done among black African adults in Africa are few and have shown that vitamin D deficiency ranges from 5-91%. In view of the difference in skin colour, latitude and vitamin D binding protein, these values might be misleading. A few cut- offs have correlated vitamin D deficiency to physiological markers such as parathyroid hormone (PTH), calcium and phosphate with varying results.
Objectives: This study was carried out to determine the proportion of healthy black African adults at AKUHN who were classified as 25(OH)D deficient using the current cut-off of 20ng/ml and to correlate this with markers of physiological deficiency, dietary intake of vitamin D rich foods and sunshine exposure.
Methods: This was a cross sectional study carried out among blood donors at AKUHN from March to May 2015. Blood was taken from consecutively recruited participants who gave informed consent and filled a questionnaire. Vitamin D levels were assayed and correlated with PTH, calcium and phosphate.
Results: A total of 258 individuals were recruited for the study. The proportion of study participants who had a 25(OH)D level of <20ng/ml thus classified as vitamin D deficient was 17.4% (95% C.I 12.73-22.07). The 25(OH)D level that coincided with a significant increase in PTH was 30ng/ml. There was no statistically significant difference in calcium and inorganic phosphate levels between Vitamin D deficient and non-deficient individuals (U=3788 p 0.06, U=4299 p 0.499). vi Males were less likely to be vitamin D deficient (O.R 0.48 (C.I 0.233-0.993) p 0.04). Sunshine exposure for ≥3 hours reduced the odds of being Vitamin D deficient though this was not statistically significant after multivariate regression analysis. The use of sunscreen and dietary intake of oily fish didn’t reduce the odds of one being vitamin D deficient.
Conclusion: This study highlights the prevalence of vitamin D deficiency in a healthy black African population based on a widely adopted cut off. Given that calcium and phosphate levels didn’t differ between vitamin D deficient and non-deficient individuals, the appropriateness of this cut off for an African population can be questioned. The vitamin D level below which there was a significant increase in PTH was similar to what has previously been found in infants at AKUHN at 30ng/ml.
Recommendations: Suitable 25 (OH)D cut-offs need to be established in the African population. This will assist clinicians and researchers in interpreting vitamin D levels in this population. The relationship between vitamin D levels and physiological markers of vitamin D deficiency such as PTH can be used when deriving such cut offs. However, since total vitamin D and not the active form is what is routinely assayed, studies correlating 25(OH)D levels, 1,25(OH)2D, vitamin D binding protein and physiological markers among Africans need to be done.
Kagotho, E. M. (2016). Vitamin D Levels in Black African Adults at the Aga Khan University Hospital Nairobi (Unpublished master's dissertation). Aga Khan University, East Africa.