"Metabolic syndrome" is a term doctors use for people who have a combination at least three of the following problems: obesity in their belly area, blood sugar difficulties (diabetes or pre-diabetes), elevated lipids (such as high cholesterol or high triglyceride levels), and high blood pressure. The research reviewed in this article found that post-menopausal women who develop metabolic syndrome have an increased risk of breast cancer, both invasive and non-invasive. Metabolic syndrome has already been shown in other research to increase the risk of developing diabetes and coronary heart disease, but this is the first research to look at the link between metabolic syndrome and breast cancer risk.
This research was one small part of the large and comprehensive study referred to as the Women's Health Initiative, or WHI. For this particular study the researchers followed nearly 4,900 post-menopausal women for an average of 8 years. 165 of these women developed breast cancer, most of which was invasive. The researchers found that breast cancer was nearly twice as likely to be diagnosed in women who developed metabolic syndrome during the 3 to 5 years before the cancer was diagnosed, compared to women who did not develop metabolic syndrome during that same period of time.
When the researchers looked at how individual parts of the metabolic syndrome affected risk among the women followed in the study, they found that elevated blood sugar levels, elevated triglyceride levels, and elevated blood pressure were problems each independently linked to an increased breast cancer risk.
The researchers aren't sure exactly how having the metabolic syndrome increases breast cancer risk. Insulin is a hormone that helps our bodies regulate blood sugar. Insulin also contributes to the growth of cells. People with metabolic syndrome tend to have insulin levels that are higher than normal (hyperinsulinemia), in part because their bodies no longer respond to normal levels of insulin. The researchers think that increased insulin levels in people with metabolic syndrome may promote the development and growth of breast cancer cells and so increase breast cancer risk.
While genetic factors contribute to the development of metabolic syndrome, this condition is largely the result of an unhealthful diet -- too many calories, too much fat, and too many simple carbohydrates -- combined with inadequate levels of exercise. Regardless of your age, the best way to avoid developing the metabolic syndrome AND help keep your breast cancer risk as low as it can be is to adopt and consistently stick to a healthy diet and lifestyle:
Visit the Breastcancer.org Lower Your Risk section to learn more about breast cancer risk and steps you can take to lower that risk.
LITTLE FALLS, N.J., June 30 (MedPage Today) -- The metabolic syndrome appears to be related to an increased risk for breast cancer in postmenopausal women, a longitudinal study showed.
Although there was no relationship with baseline presence of metabolic syndrome, identification of the condition three to five years before a breast cancer diagnosis was associated with an elevated risk of total and invasive cancer, according to Geoffrey Kabat, PhD, of Albert Einstein College of Medicine in New York, and colleagues.
In time-dependent analyses, higher blood glucose levels, triglycerides, and diastolic blood pressure were individually linked to greater cancer risk, the researchers reported in the July issue of Cancer Epidemiology, Biomarkers & Prevention.
"The metabolic syndrome could influence the risk of breast cancer through changes in a number of interrelated hormonal pathways, including those involving insulin, estrogen, cytokines, and growth factors," the researchers said.
The metabolic syndrome is defined as at least three of the following: abdominal obesity, high blood glucose, impaired glucose tolerance, dyslipidemia, and hypertension.
The condition has been associated with type 2 diabetes and coronary heart disease.
Previous studies that have looked at the contribution of the individual components to breast cancer risk have yielded mixed results, and no studies have explored the relationship with metabolic syndrome as a whole, according to the researchers.
So Dr. Kabat and colleagues used data on 4,888 postmenopausal women from the Women's Health Initiative to explore the issue. All were free from diabetes at baseline.
Through a median follow-up of eight years, there were 165 incident cases of breast cancer -- 131 invasive and 34 in situ.
Baseline presence of the metabolic syndrome was not associated with an increased risk for cancer.
Diastolic blood pressure was the only component at baseline to have a significant association with total breast cancer (HR 1.55, 95% CI 1.02 to 2.36).
However, in an analysis using repeated measurements over time, identification of the metabolic syndrome three to five years before a breast cancer diagnosis was associated with elevated risks of total (HR 1.84, 95% CI 1.12 to 3.01) and invasive (HR 1.77, 95% CI 1.01 to 3.12) breast cancer.
Among individual components, there were significant associations between elevated blood glucose and total breast cancer (P=0.04), triglycerides and total and invasive breast cancer (P=0.03 for both), and average diastolic blood pressure and total (P=0.002) and invasive (P=0.001) breast cancer.
The researchers said hyperinsulinemia may be the major mechanism underlying the relationships.
"Insulin has mitogenic activity in addition to metabolic effects and can promote cell proliferation in normal mammary epithelial cells and breast cancer cell lines," they said.
"Insulin may also contribute to tumor promotion by up-regulating the secretion of ovarian hormones," they continued.
"In theory," they said, "high glucose levels could additionally increase the risk of postmenopausal breast cancer by conferring a selective growth advantage on malignant cells, as high rates of glucose uptake and glycolysis are a common feature of malignant growth."
The researchers said some of the associations observed could have been due to chance given the number of comparisons performed and the limited number of breast cancer cases.
Thus, they said, "it would be premature to draw definitive conclusions about whether the associations with individual components or with the composite metabolic syndrome are more informative in our data [than in other studies] or how convincing a biological rationale exists for the observed associations with individual components."
The authors also noted that the study was limited by the absence of data on circulating estrogen levels.
The authors did not disclose any potential conflicts of interest.
Primary source: Cancer Epidemiology, Biomarkers & Prevention Source reference: Kabat G, et al "A longitudinal study of the metabolic syndrome and risk of postmenopausal breast cancer" Cancer Epidemiol Biomarkers Prev 2009; 18: 2046-53.
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