Prevalence and associated factors of hypertension among adults with diabetes mellitus in northern Sudan: a cross-sectional study

Hypertension and diabetes mellitus (DM), which are both non-communicable diseases (NCDs), are global public health concerns [1]. NCDs are described as the invisible epidemic, with mortality that exceeds that of maternal, perinatal, and communicable diseases [2]. Hypertension globally and in Sub-Saharan Africa is expected to increase to 1.5 billion and 125.5 million, respectively, by 2025 [2]. Africa shows the higher prevalence of hypertension 33.3% in Northern Africa and (27%) in sub-Saharan Africa [3]. Likewise, the Middle East and North Africa have the highest world-age standardized diabetes prevalence (12.2%) [4]. Hypertension is a leading modifiable risk factor for premature death and disability worldwide [2]. The co-existence of hypertension and DM has been documented in previous studies [5‐8]. The co-existence of hypertension and DM is associated a four-fold increase in mortality [9]. They are independent risk factors for micro-vascular diseases such as retinopathy, nephropathy and neuropathy [10]. Besides macrovascular complications that include coronary artery disease, myocardial infarction, stroke, congestive heart failure, and peripheral vascular disease [10]. Although, there is a difference in their pathophysiology, they show similar predisposing factors, such as heavy alcohol consumption, physical inactivity [11], obesity, genetic factors, and age ≥ 50 years [12]. Studies from Africa have shown a high prevalence of and complications related to hypertension in younger males (35–55 years), older females, the obese, and city dwellers with an unhealthy lifestyle [13, 14]. It has also been shown that unemployed status, male sex, aging, and nutritional transitions were determinants of hypertension in patients with DM [15]. High prevalence of hypertension (~ 25%) [16‐18] and DM (20.8%) [19] has been reported in different parts of Sudan. Previous studies have shown different rates of hypertension among patients with DM in different African settings [10, 20, 21].

Few studies have addressed hypertension among patients with DM in Sudan [22]; hence, we conducted this study to assess the prevalence and associated factors of hypertension among adult patients with DM in northern Sudan.

The median (interquartile) age of the 1973 enrolled patients was 58.0 (50.0‒65.0) years, and 818 (45.6%) were males. The median (interquartile) duration of diabetes was 5.0 (3.0‒9.0) years. The majority of the enrolled patients had their age ≥ 45 years. Of the  1973 enrolled participants, normal weight, underweight, overweight, and obese, were 21.7%, 1.3%, 37.1%, and 39.9% respectively (Table 1).

Of the 1,973 enrolled DM patients, 854 (47.6%) also had hypertension. The median (interquartile) age was significantly higher in diabetic patients with hypertension compared with diabetic patients without hypertension (60.0 [51‒67.0] years vs. 57.0 [50‒64.0], respectively, P < 0.001]). There was no significant difference in the disease duration (5 years [4.0‒8.0] vs. 6 years [3.0‒10.0], respectively, [P = 0.552]) or in the location. Compared with patients without hypertension, a significantly higher number of hypertensive patients were in the age group of ≥ 45 years, male, employed, obese, had diabetic foot (DF), and had uncontrolled DM (Table 2).

Logistic regression analyses showed that older patients (AOR = 1.03, 95%; CI = 1.02‒1.04), males (AOR = 2.96, 95%; CI = 2.15‒4.07), employed patients (AOR = 1.92, 95%; CI = 1.38‒2.70), obese patients (AOR = 1.59, 95%; CI = 1.21‒2.08), and patients with DF (AOR = 2.45, 95%; CI = 1.72‒3.47) were at higher risk for hypertension. By contrast, patients with Type 2 DM (T2DM) (AOR = 0.63, 95%; CI = 0.50‒0.80) were at lower risk for hypertension compared to type1 DM. There was no significant association between overweight, uncontrolled DM, and hypertension (Table 3).

The prevalence of hypertension among patients with DM in this study was 45.6%. A similar prevalence (47.7%) of hypertension in patients with DM was reported in Khartoum, the capital of Sudan [22]. The prevalence of hypertension among patients with DM in our study (45.6%) was slightly lower than among DM patients in Nigeria (54.2%) [10] and Ethiopia (59.5%) [20], and it was much lower than among DM patients in Cameroon (86.2%) [21]. The association of hypertension and DM could be explained by hyperglycemia, insulin resistance, and dyslipidemia, which promote the atherosclerosis process [28]. This process can lead to narrowing of blood vessels and increased peripheral arterial resistance, which represent the hallmark of hypertension [29]. Moreover, insulin resistance could be associated with inappropriate activation of the renin–angiotensin–aldosterone system [30].

In this study, older patients with DM were at a 1.03 times higher risk for developing hypertension than younger patients. Several previous studies (e.g., in the capital of Sudan [22], Ethiopia [20], South Africa [15], and the Kingdom of Saudi Arabia [KSA]) [31] have reported that older patients with DM were at a higher risk for hypertension than patients without DM. Vascular remodeling, endothelial dysfunction, and vascular stiffness, which are common features in hypertension, are increased by aging [32]. Moreover, aging induces macrocirculatory changes that promote tissue hypoxia, reduce arteriolar and capillary density, and increase peripheral vascular resistance [33].

In the current study, employed patients had an increased risk for hypertension compared to non-employed participants, which is consistent with similar results from previous studies [34, 35]. Occupational noise, related to work environment was specifically found to increase the risk of developing hypertension [36]. Moreover, employment is associated with better educational achievement and greater access to healthcare [34]. Conversely, one study reported unemployed status as a potential risk for hypertension in South Africa [15].

The current study showed that males had a 2.96 times higher risk to have hypertension than females, which aligned with the results of previous studies [15, 31, 37]. Gender differences may be explained by sex hormones, sex-specific molecular mechanisms, and gender influences that affect both glucose and lipid metabolisms [38]. Moreover, the risk factors of carotid intima-media thickness, carotid plaque score, and pulse wave velocity differ in men and women and reflect useful atherosclerotic parameters and high BP [39].

Our study showed a significant association between hypertension and T2DM than those with T1DM. This was in accordance with the outcome obtained from previous studies [20, 40, 41]. The coexistence of T2DM and hypertension predicts poor control of hypertension [15]. Moreover, genetically instrumented T2DM was associated with the risk of hypertension [42].

The current study found obesity was a significant risk for developing hypertension than those with normal or overweight subjects, which supported similar findings of study conducted in Khartoum [22] and in the KSA [31]. Obesity is not only linked to the risk of hypertension, but it can also predict uncontrolled hypertension [43]. DM, hypertension, obesity (Additional file 2), and metabolic syndrome are modulQ3ated by genetics and epigenetics factors and influenced by lifestyle [44]. Moreover, metabolic syndrome is also associated with novel, significant, and additional pathways through which red blood cells participate in oxidative stress-dependent mechanisms to potentiate metabolic syndrome-associated vascular complications [45]. One recent study pointed to an inverse association of a mitochondrial DNA copy number with a higher risk for metabolic syndrome [46].

The limitations of this study include that some risk factors were not addressed, such as smoking, alcohol consumption, physical activity, diet behavior, and lipid profile and other chronic illnesses such as chronic kidney disease, sleep apnea and bronchial asthma.