Obesity is known for a host of deleterious effects on the body and medical science is constantly revealing new dangers associated with a high body weight and fat percentage. One of these obesity-associated health risks is cancer. There are at least 13 types of cancers that have been linked to obesity. According to the CDC (Center for Disease Control) in the United States, almost 40% of all cancer cases in the U.S. in 2014 comprised of these types of obesity-associated cancers.
How obesity causes cancer?
The exact mechanism by which obesity causes cancer is not fully understood. Being overweight or obese has a host of adverse effects on the body and increases the risk of a host of diseases, apart from cancer. Some cancers may be linked to abnormal hormone and inflammatory chemical levels which is more likely to occur in obese people. However, this does not explain why obesity may be linked to all types of cancer.
It is also important to note that cancer may be associated with a sedentary lifestyle and certain dietary habits. Obesity as well may be linked to similar lifestyle and diet. Therefore it is also possible that it is not obesity that causes cancer but that diet and lifestyle may contribute to both obesity and cancer. For example, a high intake of red meat may account for obesity and is also known to increase the risk of certain cancers, like colorectal cancer.
Since cancer is due to some malfunction of genes in cells causing it to grow rapidly and be abnormally structured, obesity could somehow contribute to this malfunction. One theory is that chronic low-level inflammation caused by obesity may cause genetic damage but obesity and cancer may also be linked through other non-cancerous conditions which could be an intermediary between obesity and cancer.
For example, obesity increases the risk of type 2 diabetes and diabetes raises the risk of endometrial, pancreatic, liver, colorectal, breast and bladder cancers. ² It has also been observed that by controlling blood glucose levels through the use of antidiabetic drugs such as metformin, the cancer risk begins to drop. Type 2 diabetes has also been linked to obesity-linked chronic low-level inflammation which may be the cause of both diabetes and cancer.
Read more on what is cancer.
Does obesity increase cancer risk?
The evidence is growing and it has now been widely accepted by the medical fraternity that obesity may increase the risk of certain types of cancers. Large cohort studies have confirmed the cancer risk associated with obesity with at least 13 types of cancers. However, it is important to understand that these studies have not established a definitive relationship between obesity and cancer. ³
To a lesser degree, smaller studies have shown that people who undergo weight loss (bariatric) surgery have a lower risk of these obesity-related cancers. It further supports the evidence that obesity increases the risk of cancer. It is also important to note that risk does not infer causation. This means that while obesity may increase the risk of certain cancers, it does not necessarily mean that obesity causes these cancers.
Types of Cancers Linked to Obesity
Although obesity has been linked to the following 13 types of cancer, it may also increase he risk of other types of cancer. The following list is in alphabetical order and not an indication of the degree of cancer risk due to obesity.
Read more on common types of cancer.
Breast cancer risk due to obesity is mainly seen in postmenopausal women, and particularly for certain types of breast cancers when hormone replacement therapy (HRT) was never used. This obesity-cancer link has also been observed in men with breast cancer.
Colorectal cancer is a malignancy in the colon of the large intestine or rectum. It is one of the most common types of cancers in developed nations. Colorectal cancer is also the second most deadliest type of cancer that occurs in both men and women.
Endometrial cancer is a malignancy of the inner lining of the uterus (endometrium). It may also be referred to uterine cancer in general but there are also other types of uterine cancer. Obesity has been shown to increase the risk of the more common type of endometrial cancer.
Esophageal cancer is a malignancy of the esophagus (food pipe or gullet) which runs between the throat and stomach. Obesity has shown to the increase the risk of esophageal cancer, specifically esophageal adenocarcinoma, by 2 to 4 times, depending on the degree of obesity.
Gallbladder cancer is another type of cancer that is linked to obesity. This increased risk is also seen in people who are overweight. However, gallbladder cancer is three times more likely to occur in obese people than it is to arise in overweight people.
Gastric cancer is a malignancy of the stomach. Obesity has been linked specifically to gastric cardia cancer. This is cancer in the first part of the stomach (cardia) that connect to the esophagus. Gastric cardia cancer is twice as likely to occur in obese people.
Liver cancer is more common among men and twice as common among obese people. While this type of cancer is also linked to alcoholism and certain types of viral hepatitis, it may also be linked to non-alcoholic fatty liver disease. This is where fat deposits arise in the liver, often as a result of obesity.
Kidney cancer is among the top ten most common cancers in the United States. It is twice as likely to occur in both overweight and obese people, especially with one type known as renal cancer. The risk can rise substantially when a person is also hypertensive (has high blood pressure) which is more common in overweight and obese people.
Multiple myeloma is cancer of a type of white blood cell known as plasma cells. Although the increased risk is not as high as with other types of obesity-related cancers, it is still significant. Studies have indicated that obese people have a 10% to 20% greater chance of developing multiple myeloma.
Meningiomas are slow-growing tumors that arise from the lining around the brain and spinal cord (meninges). Most meningiomas are benign (non-cancerous), however, about 1 in 5 meningiomas are malignant (cancerous). The risk of meningiomas is substantially higher in obese people but even overweight people are at a greater risk.
Ovarian cancer (cancer of the ovaries) is slightly higher in obese women. As with breast cancer, the risk is greater among women who have never used hormone replacement therapy (HRT) for menopause.
Pancreatic cancer (cancer of the pancreas) is significantly higher in people who are overweight or obese. It is also more common among people with a greater abdominal circumference due to belly fat.
Thyroid cancer is among the ten most common cancers in the United States. The risk of thyroid cancer is only slightly high in people who are overweight or obese.