Vitamin D Levels in Black African Adults at the Aga Khan University Hospital Nairobi

Date of Award


Document Type


Degree Name

Master of Medicine (MMed)

First Supervisor/Advisor

Prof. Peter J. Ojwang

Second Supervisor/Advisor

Dr. Nancy Okinda

Third Supervisor/Advisor

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.

This document is available in the relevant AKU library