ReviewVitamin D deficiencies among tuberculosis patients in Africa: A systematic review
Introduction
Sun exposure as a therapeutic approach to treat tuberculosis (TB) was used more than 100 y ago, before the identification of Mycobacterium tuberculosis as the causative agent for TB [1]. Exposure of children suffering from rickets and TB to artificial ultraviolet (UV) light resulted in a positive effect on both diseases. The use of sanatoria was also based on the belief that fresh air and sun exposure led to a positive outcome in the treatment of TB [2]. Vitamin D is a known immune modulator [3] that can improve cell-mediated immunity [4] and the phagocytic capacity of macrophages [5]. It also increases the production of antimicrobial peptides such as cathelicidin [5], which is part of the innate immune system that plays a critical role in the fight against TB. Recent research highlighted the production of cathelicidin through toll-like receptor pathway [6].
Vitamin D is unique among hormones as it can be made in the skin from sun exposure [7]. Most (90%) vitamin D is synthesized in the skin under the influence of UV sunlight, and only 10% is obtained from food, mainly salmon and cod fish, and dairy products [8]. Although sunshine is abundant, TB is one of the most pernicious infectious diseases in Africa. Sub-Saharan Africa carries the greatest proportion of new cases per population, with >255 cases per 100 000 population in 2012 [9]. Almost 30% of TB cases and 34% of TB-related deaths occur in Africa [10].
Few community- and facility-based studies have been conducted with different population groups in Africa to assess the distribution of vitamin D deficiency (VDD) in patients with TB and their cause–effect relationship. These studies have provided insight into the status of vitamin D in patients with TB. However, four questions still need to be addressed:
- 1.
Is VDD common in TB patients living in Africa?
- 2.
If yes, which level of deficiency is highly predominant?
- 3.
What are the reasons for VDD in TB patients?
- 4.
What are the predictors of VDD?
Therefore, the present study was designed to address these four questions through a comprehensive systematic review of all articles published in peer-reviewed journals.
Section snippets
Data sources and search strategy
PRISMA guidelines and checklists were used to conduct this systematic review [11]. Data were collected from published articles without time restriction. Electronic searches of Medline/PubMed, Web of Science, Scopus, and Google Scholars were done through May 25, 2014. Details of the search criteria for each database were as follow:
- •
Medline/PubMed: (“vitamin d deficiency”[MeSH Terms] OR “vitamin d deficiency”[All Fields]) AND (“tuberculosis”[MeSH Terms] OR “tuberculosis”[All Fields]) AND
Search results
The literature search and selection process are schematically indicated in Figure 1. Initially, the search in Medline/PubMed, Web of Science, Scopus, and Google Scholars yielded 2919 articles. After looking through their titles and abstracts, 80 potential studies were identified; however, only 23 were included in the systematic review analysis. Fifty-seven studies were excluded because of they were duplicates (44); reviews (3); or commentaries, letters, or thesis (1 each); they included African
Discussion
The relationship between vitamin D and TB may be mediated through the mechanisms of increased cathelicidin production and enhancement of the capacity of macrophages [8]. Vitamin D is essential for an interferon-γ–mediated pathway in macrophages that leads to autophagy, phagosomal maturation, and other antimicrobial activities against M. tuberculosis [22].
Conclusion
VDD and VDI were highly prevalent among TB patients in Africa. These were attributed to the existence of predictors such as a lack of sun exposure, inadequate dietary intake, season, clothing, comorbidities, age, low BMI, skin pigmentation, use of ART and anti-TB drugs, SES, time spent outdoors, money spent on food, sex, and marital status. Understanding the problems with their predictors enable us to further question the association between vitamin D status and TB and what should be done to
Acknowledgment
The authors acknowledge Food Security Center as the first author is sponsored by Food Security Center of university of Hohenheim, which is supported by the German Academic Exchange Service (DAAD) with funds of the Federal Ministry of Economic Cooperation and Development (BMZ) of Germany.
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