High prevalence of vitamin D deficiency in African populations

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A research reviewed of all published studies that assessed the vitamin D status of healthy populations in Africa found that the average prevalence of vitamin D deficiency was much higher than expected.

Reagan Mogire, at the KEMRI Wellcome Trust Research Programme writes in The Conversation:
The prevalence of vitamin D deficiency, and the number of diseases associated with it, seems to be increasing worldwide. Africa is known to have a huge burden of disease, but little is known about the prevalence of vitamin D deficiency. In our recent paper, we reviewed and analysed all published studies that assessed the vitamin D status of healthy populations in Africa. The average prevalence of vitamin D deficiency was much higher than we expected.

Exposure to sunshine for a few minutes is enough to provide sufficient vitamin D. This is the major (and often the only) source of vitamin D for many populations worldwide. Populations that live in regions that don’t get enough sunshine especially during winter are at high risk of vitamin D deficiency. Therefore, some depend on supplements and foods fortified with vitamin D.

Vitamin D has been shown to regulate the function of 229 genes in humans. This suggests it plays many roles in maintaining health.

Research has shown that vitamin D deficiency is associated with noncommunicable and infectious diseases. For example, the deficiency has long been known to cause rickets, growth retardation and skeletal deformities in children. In adults, it can cause osteoporosis and osteomalacia and increase the risk of fractures.

More recent studies have linked vitamin D deficiency to infectious diseases, cancers, cardiovascular diseases, and autoimmune diseases.

With the abundance of sunshine all year round, it is logical to expect that populations living in Africa would have sufficient vitamin D. But there was sparse research to prove or disprove this. Our research was an attempt to fill this gap.

Our findings are important because they point to a problem that health care providers, public health policy makers and the general public in Africa should be aware of.

Africa has a big burden of both infectious and non-communicable disease. For instance, the continent records one of the highest rates of rickets in the world. A 2014 report by the World Health Organisation indicated that the burden of non-communicable diseases would surpass that of infectious diseases by 2030.

Many of these diseases, including diabetes, stroke, autoimmune diseases and cancers, to name a few, have been linked to vitamin D deficiency. To the best of our knowledge, no African country has implemented vitamin D intervention policies in its public health strategy.

The lack of proper programmes might stem from the fact that people may still believe that vitamin D deficiency isn’t a problem in Africa. One contributing factor to this misconception is the fact that there is little information on vitamin D status of people living on the continent.

In a systematic review, we set out to determine the prevalence and risk factors associated with vitamin D deficiency in Africans. We searched for – and reviewed – all published studies that measured the vitamin D status of populations living in Africa. In addition, we pooled prevalence estimates from countries across Africa to come up with an average prevalence of vitamin D deficiency.

We used three generally accepted cut-offs to define low of vitamin D levels (there is no consensus on the definition of vitamin D deficiency): severe vitamin D deficiency was defined as vitamin D levels below 30 nanomoles per litre (nmol/L) (this has been associated with increased risk of bone and mineral diseases); vitamin D deficiency as vitamin D levels below 50 nmol/L; and vitamin D insufficiency as vitamin D levels below 75 nmol/L (this is associated with other non-skeletal diseases).

On average, we found that the prevalence of vitamin D deficiency was approximately 34% using a 50 nmol/L cut-off and 18% using a 30 nmol/L cut-off. This implied that at least one in three people in Africa has vitamin D deficiency and may be at risk of bone related diseases.

Using the 75 nmol/L cut-off, about two in every three people had vitamin D insufficiency (67%), which may put them at risk of vitamin D deficiency-related noncommunicable diseases.

We found that a number of population subgroups were at a high risk of vitamin D deficiency. These included newborns, women, populations living in urban areas and populations living in northern and southern Africa. Countries close to the equator had less prevalence of vitamin D deficiency.

In separate analyses, we found the deficiency was more common in patients with diseases such as rickets, tuberculosis, diabetes, asthma and malaria.

Contrary to general expectations, our findings indicate that vitamin D deficiency is common in many populations in Africa. This may be a big public health problem, considering many of the diseases that are prevalent in Africa have been linked to vitamin D deficiency.

Governments in Africa should begin to incorporate strategies to prevent, detect and manage vitamin D deficiency in their public health and primary care programmes. These may include national policies and nutritional guidelines to improve vitamin D status, especially for populations at risk. Ensuring adequate sun exposure and dietary vitamin D intakes is a good place to start.

Abstract
Background: Vitamin D deficiency is associated with non-communicable and infectious diseases, but the vitamin D status of African populations is not well characterised. We aimed to estimate the prevalence of vitamin D deficiency in children and adults living in Africa.
Methods: For this systematic review and meta-analysis, we searched PubMed, Web of Science, Embase, African Journals Online, and African Index Medicus for studies on vitamin D prevalence, published from database inception to Aug 6, 2019, without language restrictions. We included all studies with measured serum 25-hydroxyvitamin D (25[OH]D) concentrations from healthy participants residing in Africa. We excluded case reports and case series, studies that measured 25(OH)D only after a clinical intervention, and studies with only a meeting abstract or unpublished material available. We used a standardised data extraction form to collect information from eligible studies; if the required information was not available in the published report, we requested raw data from the authors. We did a random-effects meta-analysis to obtain the pooled prevalence of vitamin D deficiency in African populations, with use of established cutoffs and mean 25(OH)D concentrations. We stratified meta-analyses by participant age group, geographical region, and residence in rural or urban areas. The study is registered with PROSPERO, number CRD42018112030.
Findings: Our search identified 1692 studies, of which 129 studies with 21 474 participants from 23 African countries were included in the systematic review and 119 studies were included in the meta-analyses. The pooled prevalence of low vitamin D status was 18·46% (95% CI 10·66–27·78) with a cutoff of serum 25(OH)D concentration less than 30 nmol/L; 34·22% (26·22–43·68) for a cutoff of less than 50 nmol/L; and 59·54% (51·32–67·50) for a cutoff of less than 75 nmol/L. The overall mean 25(OH)D concentration was 67·78 nmol/L (95% CI 64·50–71·06). There was no evidence of publication bias, although heterogeneity was high (I2 ranged from 98·26% to 99·82%). Mean serum 25(OH)D concentrations were lower in populations living in northern African countries or South Africa compared with sub-Saharan Africa, in urban areas compared with rural areas, in women compared with men, and in newborn babies compared with their mothers.
Interpretation: The prevalence of vitamin D deficiency is high in African populations. Public health strategies in Africa should include efforts to prevent, detect, and treat vitamin D deficiency, especially in newborn babies, women, and urban populations.
Funding: Wellcome Trust and the DELTAS Africa Initiative.

Authors
Reagan M Mogire, Agnes Mutua, Wandia Kimita, Alice Kamau, Philip Bejon, John M Pettifor, Adebowale Adeyemo, Thomas N Williams, Sarah H Atkinson

 

Full report in The Conversation

 

The Lancet Global Health article

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