Relying on the "Stroke Screening and Prevention Project" of the National Cerebral Prevention Commission, this study constructed a high-precision stroke risk factor pre-model composed of age, sex, exercise, meat and vegetarian diet, BMI, waist circumference, systolic blood pressure, waist-height ratio and other factors. According to a series of risk factors, the risk assessment of the impact of obesity/overweight individuals on stroke was established, aiming to provide a basis for early identification and treatment. As one of the anthropometric indicators, BMI has the characteristics of simplicity and strong operability[10], Obese individuals are more likely to suffer from various chronic diseases[11], and previous studies have used BMI as a predictor of ischemic stroke complications such as hypertension and diabetes[12, 13]. People who are overweight or obese have a higher risk of stroke, high blood pressure, diabetes and other conditions[14]. In this study, when other risk factors were not included as moderators, the greater the BMI value and the higher the OR value, the higher the risk of ischemic stroke compared to the non-stroke group. The results of multivariate regression analysis suggested that BMI was an independent risk factor for ischemic stroke, and it could also indirectly affect the incidence of ischemic stroke by influencing other risk factors related to ischemic stroke, such as hypertension, diabetes, and heart disease. Therefore, it is of great significance for the prevention and treatment of ischemic stroke in China to analyze the correlation degree and the internal influence relationship between BMI and the epidemic status of ischemic stroke in middle-aged and elderly residents in China.
At present, the research on the relationship between obesity and stroke has not reached an exact conclusion, and the research reports vary between different countries. European and North American studies[15, 16] have reported that high BMI is significantly associated with an increased incidence of stroke. Meanwhile, Epidemiological studies in Asian countries have reported[17] that high BMI is an important risk factor for death from cardiovascular and cerebrovascular diseases, including stroke. However, studies[18, 19] showed that BMI was not associated with the occurrence of any type of stroke, and even some studies[20, 21] reported better prognosis after stroke in obese and overweight patients, which is called the "obesity paradox". The results of this survey show that among the 3835 residents included, BMI is an independent risk factor for stroke. Overweight people with BMI ≥ 24kg/m2 and obese people with BMI ≥ 28kg/m2 have a significantly increased risk of stroke, and there is a statistically significant linear relationship between different BMIs and the incidence of stroke. This was consistent with the results of previous studies on stroke and obesity[22, 23], but after adjusting for confounding factors such as age and gender, the correlation between BMI and stroke outcome was weakened. We further analyzed the optimal cutoff value of BMI as an independent risk factor by using the ROC curve Jorden Index, and the predictive value of BMI for adverse outcomes (sensitivity = 0.853; 1-specificity = 0.479,; Area under the curve [AUC] = 0.768), consistent with the traditional definition of BMI ≥ 24 kg/m2, supports the importance of being overweight or obese as a predictor of stroke risk, suggesting the need for maintaining BMI within the normal range as a stroke prevention strategy.
In clinical studies and animal experiments, inflammation, and immune mechanisms have been recognized as well-established influences on stroke risk and prognosis[24, 25]. BMI, as an independent influencing factor of stroke, may be because obesity is related to the destruction of the pathways controlling lipid and glucose metabolism[26, 27], and the body is in a pro-inflammatory and hypercoagulable state, which is highly likely to cause atherosclerosis and hypertension. It may also be that the accumulation of fat promotes the increase of fibrinogen and fibrinolytic activator inhibitors in the blood, which increases the possibility of thrombosis, thus increasing the risk of stroke. In addition, inflammation has also been demonstrated in obese patients, and obesity indicators are positively correlated with C-reactive protein (CRP), interleukin (IL) -6, tumor necrosis factor α (TNF-α), and angiotensin congeners[28–30], resulting in insulin resistance and increased concentration of blood pressure-enhancing substances. Thus increasing the incidence of diabetes and hypertension, and directly resulting in impaired vascular endothelial function. However, the immune activation found in obese patients is different from that found in patients with infection or injury. Inflammation caused by obesity is a low-intensity activation of the innate immune system and affects body homeostasis over time. Therefore, obesity is described as low-grade chronic inflammation[31]. It can lead to a progressive increase in the risk of stroke. Therefore, residents should reasonably control diet strengthen exercise, and encourage overweight people with high BMI to lose weight, control body mass and keep BMI within a reasonable range to prevent the occurrence and development of stroke and other related diseases.
To sum up, the prevalence of ischemic stroke in middle-aged and elderly residents in China is significantly correlated with BMI. The prevalence of ischemic stroke is also affected by basic demographic data, lifestyle factors, dietary patterns, comorbidities, regional and county economic development levels, and other factors, thus weakening the role of BMI. However, when BMI ≥ 24kg/m2, BMI combined with other risk factors increases the risk of stroke. Our study still has certain limitations. For example, only BMI was used to assess obesity and follow-up time was not included. Further high-quality evidence is needed to clarify the relationship between obesity and stroke outcomes.