Obesity, High Blood Pressure Linked to Type of Kidney Cancer
Nov. 1, 2000 -- Obesity and high blood pressure, so often implicated in poor health and disease, now appear to be strongly related to risk for a type of kidney cancer among men called renal cell cancer, say researchers at the National Cancer Institute.
Not only are men with high blood pressure and those who are obese more likely to get renal cell cancer -- the most common form of kidney cancer -- but the risk appears to go up as weight and blood pressure go up, says Wong-Ho Chow, PhD, an epidemiologist at the National Cancer Institute in Bethesda, Md., and author of the new report.
Even more telling -- and most important for patients seeking to stay healthy -- the risk for the disease decreases as blood pressure decreases, Chow and colleagues report.
What the study demonstrates, Chow explains, is a "dose-response" relationship between the risk factors and later development of renal cell cancer: The greater the "dose" of risk factor -- either obesity or high blood pressure -- the greater the risk for later disease. Moreover, each factor appears to increase the risk for later disease independently of each other, Chow says.
"Both of these risk factors have been found consistently in previous studies," Chow tells WebMD. "What was not known was the dose-response relationship between the factors and renal cell cancer, and whether better control of these factors can decrease the risk for renal cell cancer."
While tobacco use was not a focus of the study, smoking also was implicated in a risk for kidney cancer in the study. What's the message for the public? "Control your weight, have your blood pressure checked, and quit smoking," Chow says.
Chow and colleagues examined the health records of more than 360,000 Swedish men who underwent at least one physical examination from 1971 to 1992, and followed them until death or until the end of 1995 to determine the incidence of cancer. Statistics about the men, including body mass index to check for obesity, and blood pressure, were then linked with incidence of cancer to determine the "relative risk" associated with the two factors.
What Chow and colleagues found was that men with the highest body mass had nearly double the risk for developing kidney cancer, compared with men who had the lowest body mass. There also was a direct association between higher blood pressures and higher risk of kidney cancer, she reports.
In addition, six years after the beginning of the study, subjects were checked for weight and blood pressure, a strategy that led the researchers to a crucial discovery: Regardless of the original measure of blood pressure or body mass, increases in either measure contributed to a risk for later disease.
What the study does not demonstrate conclusively are the reasons for why high blood pressure and obesity lead to renal cell cancer. But Chow and colleagues suggest some hypotheses about what those mechanisms may be: Obese persons have high concentrations in the blood of an agent known as insulin-like growth factor I, which is believed to affect the growth of cells. As for high blood pressure, changes in kidney function that accompany high blood pressure may render the organ susceptible to carcinogens and tumor growth, they suggest.