o Esophagus
o Pancreas
o Colon and rectum
o Breast (after menopause)
o Endometrium (lining of the uterus)
o Kidney
o Thyroid
o Gallbladder
1. What is known about the relationship between obesity and breast cancer?
Many studies have shown that overweight and obesity are associated with a modest increase in risk of postmenopausal breast cancer. This higher risk is seen mainly in women who have never used menopausal hormone therapy (MHT) and for tumors that express both estrogen and progesterone receptors.
Overweight and obesity have, by contrast, been found to be associated with a reduced risk of premenopausal breast cancer in some studies.
The relationship between obesity and breast cancer may be affected by the stage of life in which a woman gains weight and becomes obese. Epidemiologists are actively working to address this question. Weight gain during adult life, most often from about age 18 to between the ages of 50 and 60, has been consistently associated with risk of breast cancer after menopause.
The increased risk of postmenopausal breast cancer is thought to be due to increased levels of estrogen in obese women. After menopause, when the ovaries stop producing hormones, fat tissue becomes the most important source of estrogen. Because obese women have more fat tissue, their estrogen levels are higher, potentially leading to more rapid growth of estrogen-responsive breast tumors.
The relationship between obesity and breast cancer risk may also vary by race and ethnicity.
2. What is known about the relationship between obesity and endometrial cancer?
Overweight and obesity have been consistently associated with endometrial cancer, which is cancer of the lining of the uterus. Obese and overweight women have two to four times the risk of developing this disease than women of a normal weight, regardless of menopausal status. Many studies have also found that the risk of endometrial cancer increases with increasing weight gain in adulthood, particularly among women who have never used MHT.
Although it has not yet been determined why obesity is a risk factor for endometrial cancer, some evidence points to a role for diabetes, possibly in combination with low levels of physical activity. High levels of estrogen produced by fat tissue are also likely to play a role.
3,What is known about the relationship between obesity and colorectal cancer?
Among men, a higher BMI(body mass index) is strongly associated with increased risk of colorectal cancer. The distribution of body fat appears to be an important factor, with abdominal obesity, which can be measured by waist circumference, showing the strongest association with colon cancer risk.
An association between BMI and waist circumference with colon cancer risk is also seen in women, but it is weaker. Use of MHT (multiphasic health testing) may modify the association in postmenopausal women.
A number of mechanisms have been proposed to account for the association of obesity with increased colon cancer risk. One hypothesis is that high levels of insulin or insulin-related growth factors in obese people may promote colon cancer development.
High BMI is also associated with rectal cancer risk, but the increase in risk is more modest.
4. What is known about the relationship between obesity and kidney cancer?
Obesity has been consistently associated with renal cell cancer, which is the most common form of kidney cancer, in both men and women. The mechanisms by which obesity may increase renal cell cancer risk are not well understood. High blood pressure is a known risk factor for renal cell cancer, but the relationship between obesity and kidney cancer is independent of blood pressure status. High levels of insulin may play a role in the development of the disease.
5. What is known about the relationship between obesity and esophageal cancer?
Overweight and obese people are about twice as likely as people of healthy weight to develop a type of esophageal cancer called esophageal adenocarcinoma. Most studies have observed no increased risk, or even a decline in risk, with obesity for the other major type of esophageal cancer, squamous cell cancer.
The mechanisms by which obesity may increase risk of esophageal adenocarcinoma are not well understood. However, overweight and obese people are more likely than people of normal weight to have a history of gastroesophageal reflux disease or Barrett esophagus, which are associated with an increased risk of esophageal adenocarcinoma. It is possible that obesity exacerbates the esophageal inflammation that is associated with these conditions.
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