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TUESDAY, Aug. 5 (HealthDay News) -- Light to moderate exercise -- just walking a few blocks or even dancing -- can help prevent the abnormal heart rhythm called atrial fibrillation in those most vulnerable to it -- older people, a new study finds.

Atrial fibrillation, in which the two upper chambers of the heart tend to twitch rather than beat steadily, is the most common heart rhythm abnormality. It is especially common after age 65. The danger is that blood can pool, causing clots that move to the heart or brain. There have been reports of an increased incidence of the abnormality in younger people who exercise vigorously.

"Prior studies have looked at atrial fibrillation in young and middle-aged and generally healthy people," said study lead author Dr. Dariush Mozaffarian, a cardiologist at Brigham and Women's Hospital in Boston. "They found that, for example, marathon runners have a higher risk of atrial fibrillation. But the vast majority of atrial fibrillation occurs later in life. After 65, about one in five people develops atrial fibrillation over 10 years."

Mozaffarian and his colleagues studied the habits of 5,446 adults, average age 73, comparing their physical activities with the risk of developing atrial fibrillation.

"No one has looked at exercise and atrial fibrillation in these older people," he said. "We found that light to moderate exercise, such as walking 10 blocks a week, was associated with a lower incidence of atrial fibrillation."

Specifically, the researchers found that the incidence of the heart abnormality was 22 percent lower in those walking five to 11 blocks a week than for those walking fewer than five blocks a week. It was 24 percent lower for those walking 12 to 23 blocks weekly, 33 percent lower for those walking 24 to 59 blocks, and 44 percent lower for those walking 60 or more blocks a week.

Overall, there was a 50 percent lower risk of developing atrial fibrillation when comparing people with the highest and lowest levels of walking distance and pace.

The findings were published in the Aug. 5 issue of the journal Circulation.

Meanwhile, a separate trial looking at the effect of exercise on atrial fibrillation from a different angle is being done by Dr. Jose A. Joglar, an associate professor of internal medicine and director of clinical cardiac physiology at the University of Texas Southwestern Medical Center at Dallas.

"We have enrolled patients who have atrial fibrillation already to see whether exercise improves their quality of life," Joglar said.

The 10 participants in the trial, all in their mid-70s and diagnosed with atrial fibrillation, are doing aerobic exercises 45 minutes a day, three or four days a week, Joglar said. "They are riding stationary bicycles or walking fast," he explained.

The study is ongoing, but "preliminary data appears to be that they feel better and function better," Joglar said.

He and Mozaffarian stressed that light exercise, whatever its effect on atrial fibrillation, has known benefits, such as helping control blood pressure and weight. Other studies have shown that the right exercise -- "not too strenuous but not too light, either" -- is helpful against angina, the chest pain caused by heart artery problems, Joglar said.

"There are additional strong reasons for the public to focus on exercise," Mozaffarian said.

More information

The American Heart Association   has more on atrial fibrillation and its treatment.

MONDAY, Aug. 4 (HealthDay News) -- Updated government guidelines take a dim view of prostate cancer screenings at any age and flatly recommend against them entirely for men over 75.

The over-75 rule "is much more explicit than any recommendation out there right now" for using the prostate-screening antigen (PSA) test, said Dr. Michael L. LeFevre, a member of the U.S. Preventive Services Task Force that is updating its 2002 report.

The new recommendations are published in the Aug. 5 issue of Annals of Internal Medicine.

"The time frame is that the benefit, if there is any, from screening, is 10 years," LeFevre, a professor of family and community medicine at the University of Missouri,, added. "The average life expectancy for men over 75 years is less than 10 years, so screening them can do more harm than good."

For the same reason, men under 75 with serious health problems whose life expectancy is less than 10 years should not get, the task force report said.

Even for younger men with no health problems, "there is uncertainty about whether the benefits exceed the harm, based on existing evidence," LeFevre said.

Prostate cancer is the most common non-skin cancer in the United States, affecting one of every 6 men. Common screening tests are the PSA, which tests for protein blood levels, and a digital rectal examination, which can detect abnormal growth of the gland itself. But neither test can distinguish between prostate cancers that will become life-threatening and those that will grow so slowly that most men die with their prostate cancers, not from them.

"Most of the harms are related to treatment rather than screening," LeFevre said. Surgery and other prostate cancer treatment can cause impotence and damage urinary function and bowel function, he added.

"Men under the age of 75 should try to make an informed choice at this time," LeFevre said of screening tests. "The current evidence is not enough for us to know the balance between benefit and harm."

Current data show that a third of the men over 75 in the United States receive PSA tests, the task force report said.

A man should talk to the physician about prostate cancer screening, LeFevre said. "That discussion should occur before screening occurs and should include what the test does and does not mean, the consequences of finding cancer, and the uncertainty about whether benefit exceeds harm, based on current evidence," LeFevre said.

Medical organization make varying recommends about prostate cancer screening. The American Cancer Society position is that a test should be offered yearly to men with a life expectancy of at least 10 years, starting at age 50. Men at higher risk, such as those who have one close relative with the cancer, should begin testing at age 45, and those with several affected close relatives can have a first test at age 40, the society says.

The new guidelines "will not sit well with oncologists and a lot of people," said Dr. Susan F. Slovin, an associate attending physician who specializes in prostate cancer at Memorial Sloan-Kettering Cancer Center in New York.

"As medical oncologists, we are always trying to be one step ahead of the cancer," Slovin said. "We are trying to intervene earlier and identify patients who are at risk. We always want to intercede, to do something."

Many older men will still want prostate cancer screening, Slovin added. "These patients are very informed, and their view will be at odds with the recommendations," she said. "These are not the 75-year-olds of 50 years ago. These are physically younger people, still actively functioning sexually in many cases."

Slovin sees the screening pendulum swinging in a direction opposite to that of the new recommendation. "We are starting to make recommendations that some people be screened by the age of 35," she said.

But not everyone agrees with that assessment. Dr. Otis W. Brawley is a prostate cancer epidemiologist and chief medical officer of the American Cancer Society. He called the new guidelines, "right on target."

"The American Cancer Society since 1997 has been against mass screening," Brawley said. "But within the physician-patient relationship, a test should be offered to the patient, with the patient informed of the potential risks and potential benefits, so he can make an informed decision."

The society does not recommend against prostate cancer screening for men over 75, "but we are in the process of re-evaluating our recommendations for men of all ages," Brawley said.

In related news, the largest-ever study of its kind is shedding doubt on the prognostic value of the Gleason score, a collection of factors doctors use to gauge whether or not a patient's biopsy points to aggressive prostate cancer. The score, which ranges from 2 (least aggressive cancer) to 10 (most aggressive), is often used to decide whether men get active treatment or merely "watchful waiting."

Using biopsy and prostatectomy samples from almost 3,000 patients cared for from 1982 to 2007, researchers at the Lahey Clinic of Tufts University in Burlington, Mass., reportED that the biopsy grading system had an overall accuracy rate of only 63 percent. In fact, based on samples taken from excised prostates, 30 percent of men were found to have a higher (more aggressive) grade of cancer than their Gleason score had suggested, while 7 percent had a lower grade than the score had indicated.

The findings were published in the August issue of European Urology.

More information

Prostate cancer screening is explained by the U.S. National Cancer Institute.

TUESDAY, July 29 (HealthDay News) -- The gene most often associated with Alzheimer's disease doesn't provide a complete picture of overall risk, according to researchers who analyzed family histories of the disease.

Previous research has shown that people with the E4 variant of the APOE gene have a greater risk of developing Alzheimer's, but this new Duke University Medical Center-led study is one of only a few to examine the role of both APOE and family history together.

"We've learned that APOE genotype does not tell the whole genetic story. Other genes may be acting independently of APOE to influence someone's risk for developing the disease," lead investigator Kathleen A. Welsh-Bohmer, director of Duke's Bryan Alzheimer's Disease Research Center, said in a Duke news release.

The study included more than 5,000 people in Cache County, Utah, who were 65 and older when they were enrolled in the study in 1995. About 3,000 of the participants who provided DNA and details about their family history of Alzheimer's were grouped according to the family history of the disease and whether they had the APOE E4 variant.

"Over an average of seven and a half years of observation, the people who experienced the most significant cognitive decline had a family history of the disease and one or more copies of APOE E4," Kathleen M. Hayden, an assistant professor of geriatric psychiatry, said in the Duke news release.

"For this reason, researchers should focus not only on people at risk because of the APOE gene, but also those who have a family history of Alzheimer's disease. Conversely, studying those who survive to late old age without disease is important to discover genes that may offer protection against the disease."

The study was expected to be presented Tuesday at the Alzheimer's Association's International Conference on Alzheimer's Disease, in Chicago.

"These data provide further evidence that we must explore other genetic avenues to learn more about who is at risk for cognitive decline and dementia," Welsh-Bohmer said.

More information

The U.S. National Institute on Aging has more about Alzheimer's disease.