What Causes Kidney Cancer?

 

This year close to 40,000 Americans will be diagnosed with cancer of the kidney. About 13,000 Americans will die from kidney cancer. Both the incidence and death rate from kidney cancer are on the rise. In the past 20 years, the death rate from kidney cancer has nearly tripled according to an article in the September 20, 2006 issue of the Journal of the National Cancer Institute. “With increased early detection and treatment of small tumors, we would expect to see a decrease in mortality associated with kidney cancer,” according to the study’s senior author, Dr. Brent K. Hollenbeck. “Surprisingly, that’s not what we found. Our research shows that an increase in detection and treatment is not leading to a reduction in the kidney cancer mortality rate.” As is so often the case, modern medicine’s siren call of early detection and more aggressive treatment with surgery and/or drugs being the best hope for improving health and longevity fails to do much more than enrich the medical establishment?

 

An Ounce of Prevention Is Better than A Pound of Medical Treatment?

By far the most common type of kidney cancer is called renal cell carcinoma (RCC) and accounts for about 85% of the cases. RCC is more common in men than women and risk increases with age up until the mid-60s. A family history of RCC also increases the risk. Not much can be done about these risk factors, but growing research suggests lifestyle factors play an important role and may help explain why RCC deaths are increasing dramatically. Smoking appears to about double the risk of RCC, but for the past 30years the percentage of smokers in the US has been declining, so this cannot explain the increasing death rate from kidney cancer.

Perhaps the greatest risk factor for the development of RCC is hypertension (HTN). HTN appears to increase the risk by at least several fold. The higher the blood pressure (BP) goes, the greater the risk, but lowering BP may reduce the risk.1 HTN is on the rise again in the US, with about half of Americans age 55-64 having HTN. This trend may account for some of the increased risk of RCC.

In addition, Americans are getting fatter and the risk of RCC is at least twice as high in overweight people as it is in those with a BMI in the lower half of the normal BMI range (18.5-22). Certainly there has been a large increase in the prevalence of overweight and obese Americans and this likely is playing a significant role in the increasing death rate from RCC. Increasing body fat is known to result in insulin resistance, higher insulin levels, and elevated levels of IGF-1 and TNF-alpha, which may promote RCC. IGF-1 promotes the growth of a lot of cancers including prostate, ovarian, kidney, and no doubt many more.

Weight loss improves insulin sensitivity and lowers blood pressure, TNF-alpha and IGF-1, which suggests it may well reduce the risk of RCC. Eating a lot of refined grains was recently shown to increase the risk of RCC in Italians in a large case-control study.2

By contrast, eating more vegetables was associated with about a 35% lower risk of having RCC. An even larger study published in the January 2005 International Journal of Cancer, involving about 61,000 Swedish women, found that consuming more bananas, carrots, beets, lettuce, cucumbers, and cabbage substantially reduced the risk of developing RCC. Interestingly drinking more fruit juices was associated with a greater risk of RCC, perhaps because they are triggering excess insulin and other pro-growth hormone release. Another study of this same group of Swedish women examined the risk of RCC and the consumption of seafood over a 15-year follow-up period. The results showed that the women who ate the most fatty fish had only about one-fourth the risk of having developed RCC as the women who consumed little or no fatty fish.3 However, women who ate mostly low-fat fish did not experience a significant reduction in the risk of RCC, perhaps because such fish have far less vitamin D and omega-3 fatty acids – both of which appear to reduce the risk of several other types of cancer.

 

The Bottom Line:

The best advice for those wishing to cut their risk of RCC is to eat more fatty fish, more vegetables and fruits (not juices), and consume whole grains rather than refined grains. In addition, cutting back on salt, quitting smoking, and losing as much excess weight as possible are all likely to further reduce the risk of kidney cancer. Clearly these lifestyle changes are far more important than early diagnosis and standard medical interventions. And they are good for overall health, too.

 

By James J. Kenney, PhD, RD, FACN

 

1 N Engl J Med 2000;343:1305

2 Int J Cancer 2006 10/20/06 online report

3 JAMA 2006;296:1371

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