The threat of obesity to cardiovascular system and cancer health
A strong causal link exists between obesity and cardiovascular health. Multiple international studies have shown a significant positive correlation between obesity and the incidence of both ischemic and hemorrhagic stroke. A prospective study of 21,414 American male physicians with an average follow-up of 12.5 years showed that compared to those with a BMI <23 kg/m², those with a BMI ≥30 kg/m² had a relative risk (RR) of 1.95 for ischemic stroke (95% CI: 1.39-2.72) and an RR of 2.25 for hemorrhagic stroke (95% CI: 1.01-5.01). The data further indicated that for every 1 kg/m² increase in BMI, the RR for both hemorrhagic and ischemic stroke increased by 6%. Even after adjusting for hypertension, diabetes, and hypercholesterolemia, the risk of ischemic stroke remained significantly increased, confirming its independence.
In China, approximately one-fifth of stroke patients are overweight or obese (BMI > 23 kg/m²). A study of 24,900 participants in my country with an average follow-up of 15.2 years showed that the relative risk (RR) of ischemic stroke in the overweight and obese groups were 2.03 and 1.98, respectively. The attributable risk of ischemic stroke in overweight and obese individuals was as high as 53.3%. Another follow-up study of 212,000 men aged 40 to 79 years also confirmed that in individuals with a BMI ≥ 25.0 kg/m², stroke mortality significantly increased with increasing BMI (P < 0.001). A meta-analysis by the my country Obesity Working Group showed that for every 2.0 kg/m² increase in BMI, the risk of stroke and ischemic stroke increased by 6.1% and 18.8%, respectively. Controlling BMI to below 24 kg/m² could reduce the incidence of ischemic stroke in men and women by 15% and 22%, respectively.
Central obesity (abdominal obesity) is more closely related to stroke. A study from the University of Gothenburg in Sweden showed that, with the same degree of obesity, men with abdominal obesity have a 3 to 5 times higher risk of stroke than those with peripheral obesity. A study from the University of Southern California in the United States involving women aged 35 to 54 also found that abdominal obesity is a key risk factor for stroke in this age group. A Chinese study including 74,942 women aged 40 to 70 showed that waist-to-hip ratio (WHR), waist circumference (WC), and waist-to-height ratio (WHtR) were all closely related to stroke risk. Among the various combinations of factors associated with metabolic syndrome, hypertension combined with abdominal obesity posed the highest risk.
In the field of oncology, obesity has a similarly profound impact. A 2016 report by the International Agency for Research on Cancer (IARC) indicated a causal relationship between high body fat percentage and the risk of 13 types of cancer, including breast cancer (postmenopausal), colorectal and colon cancer, uterine cancer, esophageal adenocarcinoma, gallbladder cancer, kidney cancer, liver cancer, meningioma, multiple myeloma, ovarian cancer, pancreatic cancer, gastric cardia cancer, and thyroid cancer. Obesity may induce cancer through mechanisms such as pro-inflammatory cytokines, adipokines, and hyperinsulinemia. Studies show that nearly half of cancer cases caused by overweight and obesity occur in high-income Western countries (approximately 252,500 cases).
The relationship between digestive system cancers and obesity is particularly well-studied. Obese individuals have a 1.5 to 2.0 times higher risk of developing gastrointestinal cancers than those of normal weight. In Europe, approximately 11% of colorectal cancer cases are attributed to obesity. Obese men have a 30% to 70% increased risk of colorectal cancer. Regarding colorectal cancer (CRC), obesity increases the risk by 19%. A Japanese study found that obesity and being overweight are associated with the risk of death from colorectal cancer in Japanese women, with menopausal status being a key variable. Some studies suggest that obesity is associated with a two-fold increased risk of CRC in premenopausal women (RR=1.61).
The relationship between breast cancer and obesity has also attracted much attention. A Japanese follow-up study of 397,644 healthy individuals showed that among postmenopausal women, the risk of breast cancer increased with increasing BMI, with a significantly higher risk in those with a BMI ≥ 24 kg/m². A meta-analysis showed that women with a BMI > 30 kg/m² had a 1.3 to 2.0 times higher risk of developing breast cancer than those with a normal BMI. Obesity also leads to a poorer prognosis for breast cancer; obese women have a 2.43 times higher risk of recurrence (95% CI: 1.34–4.41) and a 2.41 times higher risk of death within 10 years. Studies on prostate cancer show that BMI is negatively correlated with localized prostate cancer but positively correlated with high-risk prostate cancer.