Prevalence of obesity, diabetes mellitus, hypertension and associated risk factors in a mining workforce, Democratic Republic of Congo

Introduction The burden of non-communicable diseases (NCDs) is increasing in low and middle-income countries (LMIC). According to the World Health Organization (WHO) the largest increase occurs in Africa. Obesity, diabetes mellitus and hypertension (ODH) are major risk factors for cardiovascular diseases, causing nearly 18 million deaths worldwide. Various risks associated with mining as an occupational activity are implicated in NCDs' occurrence. This study describes the baseline prevalence of ODH and associated risk factors in the workforce of Tenke Fungurume Mining (TFM), in southern Democratic Republic of Congo. Methods A cross-sectional study was conducted on a sample of 2,749 employees' and contractor's occupational health examination files for 2010. Socio-demographic, occupational, medical, anthropometric and behavioral characteristics were collected and assessed. Disease status regards ODH was based on WHO criteria. A multivariate logistic regression model was used. Results Overall prevalence of ODH was 4.5%, 11.7%, and 18.2% respectively. Proportions of pre-ODH individuals were 19.7%, 16.5%, and 47.8% respectively. Prevalence of ODH increased with age, professional grade, nature of work, gender and reported alcohol use. Smoking 10 or more cigarettes per day increased risk of diabetes and hypertension, while decreasing obesity. Conclusion Rates of ODH and associated risk factors are higher in the TFM workforce, than in the general DRC population. This is likely reflective of other mining sites in the country and region. It is evident that ODH are associated with various socio-demographic, occupational, anthropometric, biomedical and behavioral risk factors. A NCD prevention program and close monitoring of disease and risk factors trends are needed in this population.


Introduction
Non-communicable diseases (NCDs) currently result in more premature deaths than all other causes combined. Together they kill nearly 40 million people each year, accounting for 70% of all global deaths [1,2]. According to World Health Organization (WHO), if unabated, the number of deaths will reach 52 million annually by 2030 [3]. Cardiovascular diseases (CVD), cancers, chronic respiratory diseases and diabetes mellitus (Type 2) are the four main NCDs attributable to common risk factors [4,5]. They currently cause an estimated 82% of all NCD-related deaths namely: CVD (17.7 million deaths; 46.2%), cancers (8.8 million; 21.7%), chronic obstructive pulmonary disease (3.9 million; 10.7%) and diabetes (1.6 million; 4%) [1,6]. In 2015, nearly 80% of NCD related deaths (30.7 million) occurred in low-and middle-income countries (LMICs), with approximately 48% occurring in adults and less than 70 years of age [2]. Because of relatively higher birth rates compared to developed nations and a rapid shift in life-style, the burden of NCDs is increasing rapidly in many LMICs. The WHO projects a 17% increase in global NCD mortality over the coming decades, the largest of which (24%) will occur in Africa [7]. Obesity, diabetes mellitus and hypertension (ODH) are major risk factors for CVD, the cause of nearly 18 million deaths annually worldwide [8].
Overweight and obesity, defined as a body mass index (BMI) of ≥ 25 kg/ m² and ≥ 30 kg/m 2 , respectively, were linked to 3.4 million global deaths and 93.6 million Disability Adjusted Life Years (DALYs) in 2010 [4]. Between 2010 and 2014, the prevalence of overweight adults aged 18 and over in the Democratic Republic of Congo (DRC) had increased from 18.8% to 20.6%; while obesity rates rose from 3.7 to 4.4% [6]. By 2030, the number of diabetics is expected to reach 366 million globally. This increase will be more marked in developing countries, where the number of diabetics will rise from 84 million to 228 million [9]. Currently, the prevalence of diabetes in African countries ranges between 2 and 9% [10]. In the DRC, it has increased steadily from 5.7% to 6.1% between 2010 and 2014 [6].
It is estimated that more than 1 billion people in the world suffered from hypertension in 2000, and this number is expected to rise to nearly 1.6 billion by 2025 [11]. Hypertension is the leading CVD risk factor in sub-Saharan Africa, where more than 20 million people were already affected before 1995 [12]. According to WHO, hypertension was identified as the greatest NCD problem in the DRC in 2014; with a prevalence estimated at 24.8% and one of the highest in Africa [6].

A baseline health survey (BHS) conducted in 2008 in the Tenke
Fungurume Mining (TFM) concession located in southern DRC found 12% of respondents acknowledging they had hypertension [13].
Additionally, the same BHS found that prevalence of overweight and obesity in both sexes was 12.7% and 4.7%, respectively. Mining represents one of the most hazardous occupational activities in the world, both in terms of potential acute injuries and deaths, but also long-term health impacting exposures, resulting in various cancers and chronic respiratory diseases. Environmental exposure risks associated with mining have been implicated in the occurrence or exacerbation of NCDs. For example, occupational exposures to excessive (high decibel) noise and body vibration have been linked with increased risk for cardiovascular morbidity and mortality [14,15]. Increased levels of work-related stress, isolated living conditions, catered food service, night shift work and other factors associated with the mining industry contribute to the magnification of important risk factors resulting in disease [16,17]. In 2011, the United Nations General Assembly formally acknowledged that NCDs represent a significant challenge for development in the 21 st century and called for direct involvement of the private sector for strengthening its contribution to prevention and control [18]. The TFM is currently the largest mining operation in the DRC. The TFM workforce is made up of a large portion of young to middle aged male adults and generally representative of a cross section of DRC middle income society. The vast majority of workers have at least a secondary school education level. Despite the importance of mining to the national economy and welfare, until now, studies on prevalence and impact of NCDs and their risk factors in the mining industry have been lacking in the DRC. The aim of this initial study is to describe the burden of ODH and associated risk factors in the TFM workforce, using 2010 occupational health records. Data and analysis will serve as "baseline" information for follow-up comparison of NCDs trends in this population to gage changes in burden of disease and impact on individual health and productivity.
A better understanding of the issues and detrimental consequences to the mining sector will serve as a foundation to develop and implement integrated intervention programs to stem the alarming rise and burden of NCDs.  than females (4.6%). Forty-eight percent of smokers reported using more than 10 cigarettes a day. The proportion of individuals (n = 1,104) who regularly drank some form of alcohol (below or above 4 standard units) was 40.2%; being significantly (p < 0.005) higher in males (40.9%) than females (29.7%). Rate of those reporting alcohol use and consuming 4 or more units per day was 18.5%.

Methods
Subjects aged less than 40 years had a significantly greater prevalence of reported alcohol use (p < 0.0001) and tobacco smoking (p < 0.05).
Obesity, diabetes and hypertension: Among study subjects, 19.7% of individuals were defined as overweight "pre-obese" (BMI: 25 -29.9 kg/m 2 ); 16.5% were pre-diabetic (fasting glucose: 101-125 mg /dl) and 47.8% were pre-hypertensive (SBP: 120-139 mmHg and or DBP: 80-89 mmHg) ( Table 2). Table 3 presents the actual burden of obesity, diabetes, hypertension and cardiovascular disease (CVD) in the 2,749 subjects medically screened. The overall prevalence of obesity was 4.5% and significantly (p < 0.0001) greater among females (13.2%) than males (3.9%). The overall proportion of diabetics was 11.7%; again, females were significantly (p < 0.05) more affected than males (16% versus 10.2%). The overall prevalence of CVD was 3.2% with females having a significantly (p < 0.05) higher rate than males. The workforce prevalence of hypertension was 18.2% and significantly (p < 0.05) higher in males compared to females. The distribution by age found that the 40-44 and ≥ 45-year age groups had significantly (p < 0.0001) higher prevalence for ODH and CVD than ages below 40 ( Figure 2). Distribution by professional categories showed that managers had greater prevalence for CVD (4.5%), hypertension (38.8%) and diabetes (17.8%) than foremen and general labor (p < 0.05), while prevalence of obesity was greater in foremen (6.9%) than in the other two categories (p < 0.05). When considering nature of work (Figure 3), clerical workers had a higher prevalence for ODH than non-clerical (p < 0.05), but no difference has been found for the prevalence of CVD between the two groups (p = 0.11). Figure 4 compares ODH and CVD in counterparts reporting drinking less than 4 standard units of alcohol per day with those consuming more. Those drinking 4 or more units of alcohol per day had a significantly (p < 0.00001) higher prevalence of obesity (14.7 % vs 5.2%), diabetes (19.1% vs 9.7%), hypertension (31.4% vs 15%) and CVD (7.8% vs 2.8%). Figure 5 shows that smokers who consumed 10 or more cigarettes per day had a significantly higher prevalence for diabetes (p < 0.005), hypertension (p < 0.0001) and CVD (p < 0.0001). However, the proportion of obese workers was significantly higher among non-smokers than smokers (4.3% vs 0.2%, p < 0.0001), whereas there was no significant difference in compared to a large mining workforce located in Papua, Indonesia [19] and communities in DRC [20,21] and Fungurume [13].
However, a study of Congolese adults in South Kivu (eastern DRC) reported a nearly 40.1% prevalence. DRC is a geographically large and diverse country, thus regional differences in NCD prevalence would not be entirely surprising. For example, the high rate of hypertension in South Kivu may be related to altitude in eastern DRC (a mountainous region) where hypoxia and polycythaemia (chronic erythremia) can lead to vascular resistance by increase in blood viscosity [22]. In addition, the chronic stress resulting from long years of war and civil unrest in this region might be a significant contributor to hypertensive states. The proportion of diabetics in the TFM workforce was 11.7%, with mean fasting blood glucose of 93.9 mg/dl. Studies in the general population of DRC have reported a diabetes' prevalence ranging from 3.5 to 7% [21,23,24]. Our findings show a much higher prevalence than those reported in rural areas of sub-Saharan Africa, which are typically less than 3% [24][25][26]. The prevalence of diabetes and mean fasting glucose reported from TFM are also higher than those reported in mine workers in Papua, Indonesia (2.5% diabetics and mean 87.1 mg /dl fasting blood glucose) [19].
At TFM, overweight (19.7%) and obesity (4.5%) prevalence among mine workers is much higher than those reported for the general population of the DRC. For example, in the South Kivu region, obesity rates only reach 3.5% [27]. In the city of Lubumbashi (DRC), a location approximately 180km from the TFM concession, obesity (13.3% in adult females) was significantly associated with urbanization [28]. The prevalence of obesity in our study is lower than that reported in the COPPER survey conducted in Papua (6.8%) [19], but comparisons with a location and population in Indonesia (Australasia) should be viewed with caution.
Unfortunately, there are few other studies on mine workforce populations from which to compare. In our study, the prevalence of smoking (18.9%) and alcohol intake (40.2%) are higher than in the general population of the DRC that shows 8% and 10% for smoking and alcohol intake, respectively [29,30]. The TFM workforce obtains a regular income and is relatively well-paid compared to the general population. However, working and residing for long periods in a rural, isolated location, with many separated from their family during those periods, may explain in part, the relatively high rates of alcohol and tobacco use. Moreover, unrestricted access to food provided by the mine company may be responsible for a diet richer in sugar, salt and fat than usual [16,17] thus inadvertently promoting increases in overweight and obesity rates in the workforce. As with other studies, we confirm the role of age, professional grade, nature of work (clerical/ non-clerical), smoking and alcohol use as major risk factors for NCDs [31][32][33][34][35][36][37]. However, obesity decreased with an increase in the amount of tobacco used.
The lower probability of weight gain in smokers does not compensate for the grave health consequences of tobacco use. This study demonstrates the relatively high prevalence of certain risk factors for NCDs in a mining workforce in DRC, as smoking and alcohol abuse increase the risk of developing CVD and other NCDs [30,38]. Our results also indicate that public health efforts are needed to identify appropriate measures to reduce tobacco use and excessive alcohol intake, such as public awareness campaigns highlighting the harmful effects of both and methods to reduce or eliminate use. Primary limitations of this study were: working with archived retrospective data that had not been collected by study team, therefore some systematic errors cannot be excluded. Organized workplace programs that integrate health risk assessment measures with specific interventions (e.g. targeting dietary intake and increasing physical activity) are effective means to help abate the looming crisis of NCDs, with concomitant improvements in overall medical parameters promoting psychological and physical wellbeing [40]. For the employer, moreover, programs that improve health outcomes can lead to reductions in absenteeism and associated health care costs, while increasing productivity.

Conclusion
This baseline study found pronounced high rates of obesity, diabetes mellitus, hypertension (ODH) and associated risk factors in a mining workforce compared to the general population of DRC.
This study also provides evidence of the relationship between NCDs and various socio-demographic, occupational, anthropometric, biomedical and behavioral risk factors, in the target population.

Competing interests
The authors declare no competing interests.