Before one gets into the conversation regarding the link between obesity and cancer, one needs to understand what obesity is. Obesity refers to the condition in which a person has an unhealthy amount of body fat or distribution of the same in them, usually measured by using BMI (Body Mass Index). The calculation of obesity is done by dividing the weight of a person, usually in kilogram by their height, usually in meters.
Link of Obesity with Cancer
The link between obesity with cancer has been found by performing observational studies, usually large cohort studies.
However, the data obtained through this type of data is very difficult to interpret and the link that has been established between the two is not definite since there are various other factors than weight at play and the way the body of a lean person works usually differs from that an obese person.
However, while analyzing the risk of having cancer, it has been found that Obese people are more prone to cancers and this has prompter doctors to mark Obesity as a cause for concern. The presence of more body weight in a person causes several life-threatening diseases and one of them is cancer.
Of all cancers, obesity is linked with major cancers like Endometrial Cancer, Oesophageal Adenocarcinoma, Gastric Cardia Cancer, Liver Cancer, Kidney Cancer, Multiple Myeloma, Meningioma, Pancreatic Cancer, Colorectal Cancer, Gallbladder Cancer, Breast Cancer, Ovarian Cancer, Thyroid Cancer.
How does Obesity cause Cancer?
Obese people usually suffer from inflammation, usually from chronic low-level inflammation, which over time can cause DNA damage that results in cancer. Over-weight or obese run more risk of suffering from chronic diseases than lean people which are caused by low-level inflammation.
Fat tissues or Adipose tissues discharge an extra amount of estrogen, which has often been linked with giving rise to breast, endometrial and ovarian cancer. Obese people usually have a high level of insulin in their blood and IGF-1 (Insulin Growth Factor) in blood. This often causes diabetes in overweight people.
Adipose tissues produce Adipokines, hormones that stimulate and sometimes, inhibit cell growth. The level of Leptin, an adipokine, which promotes cell proliferation in the blood, increases with the increase in body fat.
Adiponectin which is usually produced less in people having normal weight or underweight people is found in abundance in obese people. Fat cells often have direct or indirect effects on cell growth regulators which causes cancer.
Of the cancers mentioned above, the first ten are major ones and are discussed in detail below.
Obese or more overweight women are twice or four times more likely to develop this type of cancer (cancer of the lining of the uterus) than normally weighed women.
Extremely obese women are seventy percent more prone to suffer from this type of cancer. Obese women who have never been on hormone therapy are more likely to suffer from this cancer since the excess amount of estrogen produced by the body has never been curtailed before.
High levels of insulin are also instrumental in the cause of this cancer. Higher levels of estrogen result in the production of more cells which in turn result in tumor growth. This type of cancer usually occurs after one hits the pro-menstrual stage.
People who are overweight run the risk of contracting this type of cancer which happens usually in the esophagus, twice more than lean people and severely obese people run the risk of contracting this disease four times more than normal weighing people.
Gastric Cardia Cancer
This part of the gastric, close to the Oesophagus tends to develop cells that result in cancer. The chances of obese people suffering from this form of cancer in the upper part of the stomach are 50% more than non-obese people.
Women run more risk of contracting this cancer than men, even though this can be induced by the consumption of alcohol. Obese people like the other two cancers, run the risk of suffering from this cancer twice as lean people.
Renal Cell Cancer is the most common form of Kidney Cancer and Obese people are 50% more likely to get affected by this cancer.
This association is however independent of the fact that obese people usually suffer from more blood pressure which has often been cited as a factor of kidney diseases.
Multiple Myeloma is a type of cancer in which the body develops a type of white blood cells called plasma cells. They accumulate in the bone marrow and stop the healthy white blood cells from fighting infections or diseases.
The symptoms usually include bone pain, constipation, loss of appetite, nausea, confusion, fatigue, and weight loss. The cause for this cancer remains undetected as most doctors are of the opinion that it begins with one abnormal plasma cell in one’s body. Men are more likely to suffer from this type of cancer than women.
Meningioma is the name of the tumor which forms on the membrane that covers the brain and the spinal cord, inside the skull. 90% of them are benign and are often slow-growing but in Obese people, it has been found that the risk is about 50 % more than non-obese people and in overweight people, the risk is about 20 %.
This often does not show any symptoms and hardly requires any treatment. Women run the risk of suffering from this more than men. This is often caused by genetic disorders and exposure to radiation. Cancerous Meningioma often runs the risk of spreading to the lungs as their growth is fast.
Pancreatic cancer usually occurs in the tissues surrounding the pancreas in the lower part of the stomach. The tumors can either be cancerous or non-cancerous in nature.
The most common type of pancreatic cancer is Pancreatic Ductal Adenocarcinoma which occurs in the cells that are present in the lining which carries digestive enzymes out of the pancreas.
It usually does not show any symptom until it has spread to the other parts of the body as a result of which it is often not cured at the early stage. People with Obesity run the risk of suffering from this cancer 1.5 times more than people with normal body weight.
Colorectal cancer refers to cancer that occurs in the colon or in the rectum. It can be called Colon cancer or Rectal cancer depending on the area where it occurs. The colon and Rectal make up the Gastrointestinal System and cancer usually starts with polyps in either of the places.
There are three types of polyps namely Adenomatous polyps, Hyperplastic polyps and inflammatory polyps, Sessile serrated polyps (SSP), and traditional serrated adenomas (TSA).
Out of the three, the third runs the highest risk of colorectal cancer. One’s risk of having this cancer increases if a polyp is more than 1 cm, if there are more types of polyps than the aforementioned ones and if Dysplasia is seen in the polyp after it has been removed from the body. People who are slightly obese run the risk of contracting this cancer more than people of normal body weight.
Gallbladder Cancer usually is signified by abnormal cell growth in the gallbladder. It usually is very uncommon and if found in the body early, chances are it can be cured. However, this type of cancer is discovered in the body quite late as a result of which the cure is quite poor and the chances of survival are quite less.
The symptoms usually consist of abnormal pain and bloating in the abdomen and weight loss. Obese people run the risk of having this cancer by at least 20% more than normally weighed people.
Does losing weight reduce the Risk of Cancer?
Since the data are collected through large cohort cases, they are difficult to interpret and it is difficult to say how the loss of effect reduces the risk of cancer in obese people because their body differs from the way lean people’s bodies work.
Though many studies have explored the association of cancer with obesity, fewer studies have looked into how the weight loss of obese people affects their risk of suffering from cancer. Those who have delved into this, have found that reduction in body weight significantly lowers the chances of developing breast cancer, endometrial cancer, colon, and prostate cancer.
These studies, however, failed to identify the reason behind the weight loss, was it intentional or unintentional? The studies were usually done on people who had undergone bariatric surgery (surgery usually performed on the stomach or intestine to induce the loss of excess body weight).
These people who have performed the surgery run lower risks of suffering from cancer than people who have not performed this surgery. This study is contradicted if one considers the results achieved by the Women’s Health Initiative as they found that women with reduced weight do not run less risk of suffering from breast cancer as a 5% increase in the bodyweight of a woman can induce breast cancer.