This study aimed to estimate the IDR of T2DM among patients with HTN and vice versa and to assess the relationship between T2DM and HTN as risk factors for each other. We found that the IDR of T2DM among patients with HTN was 73.9 per 1000 person-years (95% CI 56, 92), which closely aligns with the findings of a study conducted in Qatif, Saudi Arabia, where the IDR was 82.9 per 1000 person-years [20]. However, this was higher than the rate reported in China, where the IDR was 16.93 per 1000 person-years [21]. Conversely, the IDR of HTN among patients with T2DM was 55.9 per 1000 person-years (95% CI 42, 70), which aligns with another study conducted in Ethiopia reporting an IDR of HTN among patients with T2DM of 58.05 per 1000 person-years [22]. Nevertheless, this is lower than the rates reported in previous studies in Saudi Arabia and South Asia, where the IDR of HTN was 172.0 and 82.6 per 1000 person-years, respectively [23, 24]. Variations in the IDR could be attributed to differences in sociodemographic characteristics, healthcare services, and study settings.
The IDR of T2DM was 33.9 per 1000 person-years (95% CI 24, 44) in the control group, slightly lower than that reported by a study conducted in the USA (among the Pima population), where the IDR of T2DM was 38.9 per 1000 person-years [25]. However, it was significantly higher than the findings of other studies conducted in the USA (among the South Asian population) and China, where the IDR of T2DM was 16.1 and 13.4 per 1000 person-years, respectively [25, 26]. The IDR of HTN was 20.8 per 1000 person-years (95% CI, 13, 28), higher than the findings from studies conducted in Tabuk, Saudi Arabia, and Korea, where the IDR of HTN was 7.0 and 14.7 per 1000 person-years, respectively [27, 28]. However, this is lower than the finding of another study conducted in the USA, in which the IDR of HTN was 34 per 1000 person-years [29]. The findings of this study fall within the range of results observed in other studies conducted in different populations with different sociodemographic characteristics.
The relationship between HTN and T2DM in terms of their respective incidence is shown by comparing the IDR of each type and in the control group. This study revealed that the crude IDR of T2DM among patients with HTN was higher than the crude IDR of HTN among patients with T2DM (73.9 and 55.9 per 1000 person-years), suggesting that HTN may pose a higher risk factor for T2DM than vice versa. However, in comparison to the control group and after adjusting for confounders, we observed that patients with T2DM were more likely to develop HTN compared with those without the disease, whereas patients with HTN had a higher chance of developing T2DM than did those without the disease. Based on ORs, the risk of HTN in patients with T2DM was higher than the risk of T2DM in patients with HTN.
Diabetic kidney disease and cardiovascular complications can explain T2DM as a risk factor for HTN (30). In T2DM, hyperfiltration is linked to compromised renal autoregulation, leading to elevated arterial pressure [31]. Insulin resistance and DM can promote arterial stiffening, subsequently leading to HTN [30, 32]. Conversely, individuals with HTN have a higher progression rate of insulin resistance over time [33]. This is attributed to HTN-induced endothelial dysfunction, leading to adipose tissue inflammation and insulin resistance [34].
Age, smoking status, FH of HTN, T2DM status, and BMI significantly predicted HTN. The primary predictor of HTN in the model was a FH of HTN, followed by T2DM. HTN predictors are corroborated by the findings of other studies in Ethiopia and Saudi Arabia [22, 23]. The factors that significantly predicted T2DM were age, sex, FH of T2DM, HTN, and BMI. The primary predictor of T2DM in the model was a FH of T2DM, followed by BMI and HTN. T2DM predictors are supported by the findings of other studies in Saudi Arabia and China [20, 21].
The retrospective cohort design of this study allowed us to observe whether exposure preceded the outcome, potentially suggesting a causal relationship (although not as definitive as a prospective design). However, this study has a few limitations. A significant proportion of patients believe that primary healthcare centers are not ideal for monitoring and following up on their chronic conditions. Therefore, when a new health incident occurs, they autonomously decide to seek follow-up in a hospital or a larger medical center. This self-directed decision-making by patients may obscure the documentation of a new health incident, potentially leading to underestimated study findings. Therefore, follow-up studies should be conducted in hospitals or specialized medical centers. Furthermore, there are very few previously published studies specifically addressing the relationship between HTN and T2DM, which could serve as a point of comparison.