Fish Matters: Swedish Health Institute links certain fish to lower kidney cancer risk

Put down the tuna steak and opt for some salmon instead, says a Swedish health institute.

According to the Karolinska Institutet, fatty fish like salmon have 20 to 30 times more omega-three fatty acids than lean fish like tuna and cod and this can help save your kidneys.

In a 15-year cohort study of women in Sweden, the Institutet found women who ate fish rich in omega-three fatty acids at least once a month for the duration of the study were 74 percent less likely to develop kidney cancer. Eating lean fish like tuna had no effect.

"We had hypothesized this would be the relationship," said principal author and professor in nutrition epidemiology at the Institutet Alicja Wolk, "but we were surprised to see the relationship was so strong."

Besides having significantly lower omega-three fatty acid levels, lean fish also have three to five times less vitamin D than fatty fish (research from the University of San Diego links a deficiency in Vitamin D3 with a higher risk of renal cancer).

The study, a first in its scope, was a part of The Swedish Mammography Cohort. While the results are encouraging, urologists are not entirely convinced that eating fatty fish will result in lower kidney cancer diagnoses. The message is clear, however, eating fish rich in omega-three fatty acids is part of a healthy diet everyone should adopt.

The Study

The Swedish institute received 61,433 responses from women who were sent questionnaires between 1987 and 1990 about their diet. In 1997, the institute found 36,664 of these women still alive and in the area and gave them questionnaires again about their diet. The last set of the surveys was given out in 2004 and showed a total of 150 incidents of renal cancer had taken place amongst the women being studied.

In the first questionnaire, researchers found that women who ate fatty fish rich in omega-three acids once a week were 44 percent less likely to get renal cancer. After the second questionnaire in 1997, researchers found long term results were even better—women who ate the fish just once a month reduced their chances of getting renal cancer by 74 percent.

One reason these fatty fish help reduce woman’s chances of renal cancer is because, the study said, omega-three acids help our bodies suppress cancer-helping molecules and aid our immune system to help kill off cancer-causing cells.

Fish Folly

But there are follies with the study say urologist John Hollingsworth at the Michigan Urology Center in Ann Arbor, part of the University of Michigan.

"Their data is inconclusive at this time," said Dr. Hollingsworth. "This was a cohort study. You can look at associations but you can’t prove causalities. It’s an interesting finding, but doesn’t prove causality."

One reason the study is faulty is because it assumes all diets are alike, said Dr. Hollingsworth. A Swedish diet and an American diet, even with the same amount of fatty fish intake, remain very different overall. The study also relies entirely on women to remember and not falsify what they ate and how much they ate. People usually tend to make themselves look a bit better on a survey than what they eat in reality.

Perhaps the biggest fault with this study, however, is the institute did not ask about family history of renal cancer, one of the leading causes of the disease.

Kidney Cancer’s Face

There are three types of kidney cancer, but renal cell cancer, also called gurnistical tumor, is the most common form. Renal cell cancer strikes up to 85 percent of those who are diagnosed with kidney cancer. Men are about two-thirds more likely to get renal cancer than women and the average age for diagnosis is 62. The exact cause is unknown, but having a genetic mutation to the gene called VHL greatly increases your risk.

On average there are about 30,000 new cases a year; last year about 39,000 new cases were diagnosed. A total of 200,000 people are living with the disease within the United States today, said Bill Bro, chief executive of The Kidney Cancer Association based in Evanston, Ill.

Kidney cancer specialists claim there is a rise in diagnoses of renal cancer, but they are not sure why. The rise could be attributed to greater use of technology like magnetic resonance imaging machines (MRIs), ultrasounds, and X-ray machines, or the increased effectiveness of said machines. Another reason could be that baby boomers are getting older and more people are living longer than ever before.

Like Mr. Bro, many renal cancer patients go into the hospital or a doctor’s office unaware they have the disease.

"I thought I had a kidney stone," said Mr. Bro. "I was very surprised to find out what it was."

Mr. Bro had symptoms like urinating blood and back pain, but many patients do not have any symptoms at all. Most renal cancer patients first go into the hospital for an X-ray for a broken hip or a scan for some other ailment only to find out that they also have a tumor in one of their kidneys, said Dr. Hollingsworth.

Thankfully, if caught early, removing the tumor can usually cure the disease. But maintaining a healthy lifestyle and diet are always an important step as well.

As with any healthy lifestyle, quitting smoking is the most important change to make. Smoking, obesity, abusing over-the-counter pain killers, and overusing diuretic medicine, along with exposure to solvents and petroleum, are all linked to kidney cancer.

Exercising at least three times a week for thirty minutes, quitting smoking, eating a healthy diet that includes fish high in omega-three fatty acids, and limiting medicinal intake as much as possible, are good steps in taking on a healthy lifestyle, said Dr. Hollingsworth.

"Treat your body like a temple," he said.