Abstract
Background: There is growing evidence of an association between low vitamin D and HIV disease progression; however, no prospective studies have been conducted among adults receiving antiretroviral therapy (ART) in sub-Saharan Africa.

Methods: Serum 25-hydroxyvitamin D (25(OH)D) levels were assessed at ART initiation for a randomly selected cohort of HIV-infected adults enrolled in a trial of multivitamins (not including vitamin D) in Tanzania during 2006–2010.

Participants were prospectively followed at monthly clinic visits for a median of 20.6 months. CD4 T-cell measurements were obtained every 4 months. Proportional hazard models were utilized for mortality analyses while generalized estimating equations were used for CD4 T-cell counts.

Results: Serum 25(OH)D was measured in 1103 adults 9.2% were classified as vitamin D deficient (<20 ng/ml), 43.6% insufficient (20–30 ng/mL), and 47.2% as sufficient (>30 ng/mL). After multivariate adjustment, vitamin D deficiency was significantly associated with increased mortality as compared to vitamin D sufficiency (HR: 2.00; 95% CI: 1.19–3.37; p = 0.009), whereas no significant association was found for vitamin D insufficiency (HR: 1.24; 95% CI: 0.87–1.78; p = 0.24). No effect modification by ART regimen or change in the associations over time was detected. Vitamin D status was not associated with change in CD4 T-cell count after ART initiation.

Conclusions: Deficient vitamin D levels may lead to increased mortality in individuals receiving ART and this relationship does not appear to be due to impaired CD4 T-cell reconstitution. Randomized controlled trials are needed to determine the safety and efficacy of vitamin D supplementation for individuals receiving ART.

Introduction: In 2002 only 2% of HIV-infected individuals eligible for antiretroviral therapy (ART) in sub-Saharan were receiving treatment, while by the end of 2010 this proportion increased to 49% with over 5 million people receiving ART [1]. Despite successes in expanding treatment coverage, individuals initiating ART in sub-Saharan Africa experience high mortality rates and interventions are needed to prolong and improve quality of life [2], [3].

Vitamin D is a potent immunomodulator with effects on both adaptive and innate immune responses [4], [5]. Vitamin D may play a particularly strong role in control of intracellular pathogens by enhancing cell-mediated immunity, production of antimicrobial peptides, and phagocytic activity of macrophages [6]–[9]. As a result, HIV-infected individuals with adequate levels of vitamin D may better control HIV or opportunistic infections compared to deficient individuals [10]. Further, vitamin D has effects on multiple organ systems and HIV-infected individuals with low levels of vitamin D could experience increased complications of ART including: cardiovascular disease, insulin resistance, and renal impairment [11]–[13].

Three previous cohorts have investigated the association of vitamin D status and HIV mortality; however, each of these studies has methodological or generalizability limitations. The first small study conducted in Norway before introduction of ART found that HIV-infected individuals with low 1, 25(OH)2D (active form of vitamin D) had significantly decreased survival time compared to individuals with normal levels [14]. However, serum 1,25(OH)2D is considered a sub-optimal measure of vitamin D status and serum 25-hydroxyvitamin D (25(OH)D) is the only vitamin D metabolite that should be employed to assess vitamin D status [15]. The second study, consisting of HIV-infected pregnant women in Tanzania not receiving ART, found women in the highest quintile of 25(OH)D, had 42% lower risk of all-cause mortality as compared to those in the lowest quintile [16]. Low vitamin D was also associated with wasting, anemia, and incidence of acute upper respiratory infections in these women [17], [18]. Nevertheless, these results may not be generalizable to men and non-pregnant women receiving ART since pregnancy and antiretroviral drugs can interact with vitamin D metabolism and the role of vitamin D may be altered during immune reconstitution [19], [20]. The third cohort study consisted of adults in 31 European countries, Israel, and Argentina who were mostly receiving ART and similarly found adults in the highest tertile of 25(OH)D had a 0.56 times the rate of mortality compared to individuals in the lowest tertile [21]. However, these finding may not be generalizable to individuals receiving ART in resource-limited countries. Individuals receiving ART in developing countries initiate at significantly lower CD4 T-cell counts and have higher risk of comorbid infections, which may modify the impact of vitamin D on mortality [22].

To date no longitudinal studies of vitamin D and HIV disease progression have been conducted among adults receiving ART in sub-Saharan Africa or for men and non-pregnant women in a resource-limited setting. Examining the relationship between vitamin D and HIV disease progression in this population is essential given over one million adults initiated ART in sub-Saharan Africa in 2010 and coverage is rapidly expanding [1]. Furthermore, no studies have investigated the impact of vitamin D on change in CD4 T-cell count in HIV-infected individuals receiving ART in a resource-limited setting where individuals start ART at low CD4 T-cell counts, which will give valuable insight to the mechanism of vitamin D on mortality. Here we present a prospective cohort study of Tanzanian adults initiating ART to address these knowledge gaps.