Obesity, Diabetes Linked to Cancers

Obesity, Diabetes Linked to Cancers
FRIDAY, Dec. 7 (HealthDay News) -- Obesity and diabetes -- riskfactors so often linked to heart disease -- can also affect the incidenceand severity of cancer, a collection of four new studies suggests.
The findings, presented Friday at the American Association for CancerResearch's Sixth Annual International Conference on the Frontiers ofCancer Prevention Research in Philadelphia, link weight gain and diabetesto a number of malignancies, including breast, prostate and colorectalcancer.
"All of these are consistent with what we would expect with theoccurrence of each of these cancers or cancer survival," said ElizabethPlatz, associate professor of epidemiology at the Johns Hopkins BloombergSchool of Public Health. "Metabolic perturbations enhance certain cancers.Insulin and other hormonal factors influence cell growth and make cellsmultiply."
Women with diabetes have a 50 percent increased risk of developingcolorectal cancer, according to the first study, by researchers at theUniversity of Minnesota. The group, led by Andrew Flood, assistantprofessor of epidemiology and public health, followed more than 45,000women enrolled originally in a breast cancer detection program for morethan eight years.
The increased incidence of colorectal cancer remained significant afterall possibly confounding factors were taken into account. While the reasonfor the increased risk is not known, Flood said it could be due to theelevated levels of insulin seen with diabetes.
High levels of insulin in diabetic women could explain a threefoldhigher risk of death from breast cancer, said the second study, byresearchers at Yale University. They measured blood levels of C-peptide, amarker of insulin secretion, in women in a long-term study of breastcancer. Over an eight-year period, the women in the highest third ofC-peptide levels had twice the risk of dying from breast cancer, comparedto women in the bottom third, the researchers said.
Another study, by researchers at the Johns Hopkins Bloomberg School ofPublic Health, found that weight gain after a diagnosis of invasive breastcancer could significantly increase a women's risk of death from thecancer.
The study of more than 4,000 women with breast cancer classified themby body mass index, a ratio of weight to height. For obese women, the riskof dying of breast cancer was 2.4 times greater than for women with anormal body weight, a relationship that persisted when age, menopausalstatus and smoking were taken into account.
Another Johns Hopkins study provided a possible explanation for thelower risk of prostate cancer seen in men with diabetes. The researchersmatched 264 men diagnosed with the cancer with a group of 264 cancer-freemen, measuring C-peptide levels in both groups.
Men with elevated blood levels of C-peptide when the study started wereone-third less likely to develop prostate cancer than those with lowerlevels. Men with higher C-peptide levels had half the risk of developingprostate cancer confined to the prostate.
The protective effect of those high levels could be due to the activityof insulin in relation to the male hormone testosterone, Plantz said.C-peptide derives from the same parent molecule as insulin, and insulin isknown to reduce the activity of testosterone, which stimulates the growthof prostate cancer, she said.
The possible protective effect of insulin against prostate cancer couldoffer a mirror image of the negative effect of estrogen -- the female sexhormone -- in breast cancer, said Dr. Rexford Ahima, professor of medicineat the University of Pennsylvania.
"We have known for years that women who are obese are at high risk ofbreast cancer," Ahima said. "Fat tissue makes estrogen, which promotesbreast cancer. The frightening thing is that the more obese you are, thegreater the risk you have of dying of cancer. For every increase of 10kilograms, 14 pounds, there is a 14 percent increased risk of breastcancer death."
So, instead of thinking of obesity just as a risk factor for heartdisease, its effects on cancer must also be taken into account, Platzsaid. "In general, it is a good thing to do to avoid obesity," she said."That is a message consistent with what we know about good health."