Overweight/Obesity, Diabetes, and Cancer Are Closely Linked

The relationship between diabetes and cancer has long drawn medical attention, and a large body of epidemiological research has confirmed that both type 1 and type 2 diabetes carry a high risk of concurrent cancer. Diabetes patients have a higher probability of developing cancer than non-diabetic people. Some type 2 diabetes patients taking the glucose-lowering drug metformin also show suppressed cancer progression, so that in recent years some reports even call metformin a miracle anticancer drug rediscovered from an old medicine.

In 2018, a team led by Professors Shi Yang and Shi Yujiang of Fudan University Institutes of Biomedical Sciences published a study in Nature showing that the high-glucose environment caused by diabetes affects the activity of tumor-suppressor genes, thereby increasing cancer risk.

Professor Shi Yujiang team found through experiments that high blood sugar significantly inhibits the activity of AMPK protein kinase in the body, leading to reduced TET2Ser99 phosphorylation and lower TET2 protein stability, reducing the TET2-catalyzed production of 5hmC. When 5hmC decreases, the likelihood of tumorigenesis increases. They also found through experiments that the glucose-lowering drug metformin can activate AMPK, phosphorylate downstream TET2, enhance TET2 stability and its product 5hmC, and thereby inhibit tumor growth. This study reveals the biological mechanism behind why diabetes patients are prone to cancer and why metformin suppresses cancer.

There have been many studies on how type 1 and type 2 diabetes increase cancer risk. One study showed that in type 1 diabetes, the risk of gastric cancer increases 23% in men and 78% in women; liver cancer 2-fold in men and 55% in women; pancreatic cancer 53% in men and 25% in women; endometrial cancer 42%; and kidney cancer 30% in men and 47% in women. Of course, type 1 diabetes does not only increase cancer incidence—it can also lower the incidence of certain cancers, such as breast cancer in women and prostate cancer in men.

Among type 2 diabetes patients, those with a BMI (body mass index) above 25 have a greatly elevated cancer risk; some studies show that such patients have a 30-50% higher risk of cancers such as colorectal and breast cancer than normal people. This phenomenon is more pronounced in developing countries; the largest increases in cancer due to diabetes, overweight, and obesity occur in low- and middle-income countries in Asia and sub-Saharan Africa. In these regions, the prevalence of both diabetes and high BMI has risen significantly in recent years. Nauru islanders esteem plumpness as beauty; its diabetes prevalence was only 2% in the 1960s, rising to about 40% by the 1970s.

Modern lifestyle makes people more prone to obesity. We have left physical labor behind without taking up sports habits. Data from the FAO show that meat intake exceeds recommended levels in most contemporary countries, so obesity has become a global problem.

Obesity results from excessive calorie intake paired with relatively insufficient physical activity. Obesity, especially abdominal obesity, easily leads to insulin resistance, which in turn causes diabetes. Excess accumulated fat also easily leads to overexpression of inflammatory and growth factors, weakening the body cancer-suppressing effect. So among patients with both cancer and diabetes, obese people are in the majority.

Research has found that when body weight exceeds ideal weight by 30%-40%, insulin sensitivity drops by about 50%, greatly raising the risk of both diabetes and cancer. In China, diabetes is closely linked to obesity: diabetes prevalence is 3.37% among overweight or obese people but only 0.76% among normal-weight or thin people. Currently over half of Chinese people are overweight or obese. So for a long time to come, diabetes and cancer rates among Chinese residents will remain high.

To reduce China diabetes and cancer incidence, promoting sports nationwide and advocating healthy diets are imperative. Among Chinese adults, only 18% currently keep exercising. Comparing this figure with the overweight and obesity rates, we can understand why China has so many diabetes and cancer patients.

Ancient Chinese TCM also recognized that diabetes (xiaoke, wasting-thirst) and yongju (sores and ulcers, i.e., tumors) tend to occur in obese patients who overindulge in rich, greasy, fine foods. Lacking detailed statistics, ancient doctors nonetheless reached this correct conclusion through years of clinical experience.

Among the cancer patients I have encountered, a considerable number also have diabetes. In some, cancer came first; in others, diabetes came first. Most of these patients have poor dietary and lifestyle habits, eating too much high-fat, high-sugar food and lacking exercise.

In ancient times, only rich families generally got this disease, so it was also called the disease of affluence. Chen Shiduo, a famous physician of the late Ming/early Qing, was known for treating external sores and ulcers. In his book Dongtian Aozhi he noted that most of the sore-and-ulcer patients he treated were wealthy families in the capital. According to him, many such patients then underwent cutting treatment (i.e., surgery of the time, with very poor disinfection and anesthesia conditions), suffering enormous pain during treatment, with low success rates.

So in daily life, watching your diet, moving your legs, and monitoring your weight are very important; when BMI is too high, working hard to lose weight is crucial. Being overweight for too long, or having a high BMI after forty, with abdominal obesity (what we call middle-age spread or a general belly), increases the risk of diabetes and cancer; we should keep this from happening to us.