Tag: Cancer

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101 on Radiation Injury and the Risk of Cancer

Do you think we are totally screwed? Almost every day there is a disaster somewhere on this planet. People are left injured, homeless or dead. But some of us are lucky to be alive and well…sort of…considering the miserable weather and the potholes we always complain about.

What is happening to Japan’s nuclear reactors is scary. Then we have experts who remind us of Chernobyl, Three Mile Island, Hiroshima and Nagasaki. As part of my research for this article, I thought I will find out more about these places where nuclear disasters have occurred.

The list is long. And the list has only reported the proximate confirmed human deaths and has not detailed ecological, environmental or long term effects such as birth defects or permanent loss of habitable land. That tells me that most of us are totally ignorant of the amount of radiation damage being inflicted on us by these nuclear reactors.

These nuclear reactors are also a great source of energy and provide us with many comforts which we take for granted. Radiation is a form of energy that is present all around us. Different types of radiation exist, some of which have more energy than others.

There are two types of radiation energy:

-Non-Ionizing radiation is low-frequency radiation that does not have enough energy to remove electrons or directly damage DNA. Low-energy UV rays, visible light, infrared rays, microwaves and radio waves are all forms of non-ionizing radiation.

-Ionizing radiation has enough energy to damage the DNA in cells, which in turn may lead to cancer. Gamma rays, x-rays, some high-energy UV rays, and some sub-atomic particles such as alpha particles and protons are forms of ionizing radiation. In general, radiation is a word used for ionizing radiation.  

Due to an accident, natural disaster or by an act of terrorism the nuclear reactors are disrupted leading to environmental radioactive contamination and radiation exposure.  Such a release exposes people and contaminates their surroundings and personal property. That is serious stuff. Our body can absorb small amount of radiation but severe exposure is harmful.

One aspect of radiation exposure we often forget is the low-dose ionizing radiation from the x-ray departments when we are sent there for various kinds of investigations. A recent paper in the Canadian Medical Association Journal (Mar 8, 2011) reported a study involving 82, 861 patients, 77 per cent of them had undergone at least one cardiac x-ray or treatment procedure involving low-dose ionizing radiation in the first year after a heart attack.

Patients included in the study had no history of cancer. In a 10-year follow-up, a total of 12, 020 incident cancers were diagnosed. Risk of cancer was dose dependent and had a cumulative effect.  

Let me not scare you. Exposure to ionizing radiation from a single x-ray test does not pose a substantial risk to individual patients. But numerous tests can result in a cumulative exposure that represents a substantial risk to the patient. And remember, we do not have any mechanism to track cumulative doses of radiation in individual patients.

Currently, we have no way of knowing how much danger we face from what is happening in Japan. That does not mean we should not worry about it. But we should also worry about the radiation exposure from the sun, x-ray machines, cell-phones and other devices.

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What’s the role of exercise in preventing cancer?

Heavy weight and large size have been associated with increased risk of breast cancer. There is evidence to suggest that regular exercise is associated with a reduced incidence of breast cancer.

The relationship between physical activity and breast cancer incidence has been extensively studied, with over 60 studies published in North America, Europe, Asia, and Australia. Most studies indicate that physically active women have a lower risk of developing breast cancer than inactive women.

In the Women’s Health Initiative Observational Study published in 2001, it was reported that current exercise and exercise after menopause are both associated with a decreased risk of breast cancer. Even a small amount of exercise (1.25 to 2.5 hours per week of brisk walking) is beneficial. Women who had engaged in regular strenuous exercise at age 35 had a 14 per cent decreased risk of breast cancer compared with less active women (CMAJ 2004).

Evidence from population based studies suggests that occupational, leisure, and household activities are associated with about 30 per cent reduction in breast cancer rates – more you exercise, better the results (BMJ editorial 2000).

There is evidence to support potentially important protective effect of physical activity against colon cancer but not against rectal cancer. And there is no evidence that exercise increases the risk of any cancer. Colorectal cancer has been one of the most extensively studied cancers in relation to physical activity, with more than 50 studies examining this association (www.cancer.gov).

Many studies in the United States and around the world have consistently found that adults who increase their physical activity, either in intensity, duration, or frequency, can reduce their risk of developing colon cancer by 30 to 40 per cent relative to those who are sedentary regardless of body mass index (BMI), with the greatest risk reduction seen among those who are most active.

The risk of colorectal cancer begins to increase after age 40 and continues to increase as you get older. Obesity is linked to an increased risk of colorectal cancer. A lifestyle that does not include regular exercise may also be linked to an increased risk of colorectal cancer.

Research findings are less consistent about the effect of physical activity on prostate cancer, with at least 36 studies in North America, Europe, and Asia. Overall, the epidemiologic research does not indicate that there is an inverse relationship between physical activity and prostate cancer.

About 20 studies have examined the role of physical activity on endometrial cancer risk. These studies suggest that women who are physically active have a 20 per cent to 40 per cent reduced risk of endometrial cancer, with the greatest reduction in risk among those with the highest levels of physical activity. Risk does not appear to vary by age.

At least 21 studies have examined the impact of physical activity on the risk of lung cancer. Overall, these studies suggest that the most physically active individuals experience about a 20 per cent reduction in risk.

In conclusion, there is convincing evidence that physical activity is associated with a reduced risk of cancers of the colon and breast. Several studies also have reported links between physical activity and a reduced risk of cancers of the prostate, lung, and lining of the uterus (endometrial cancer).

Despite these health benefits, recent studies have shown that more than 50 per cent of the population do not engage in enough regular physical activity.

National Cancer Institute (NCI) funded studies are exploring the ways in which physical activity may improve the prognosis and quality of life of cancer patients and survivors. For more information about current research in this area, please visit NCI’s Cancer Survivorship Research Web site at http://cancercontrol.cancer.gov/ocs on the Internet.

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Controversial Role of PSA in Early Detection of Prostate Cancer

Controversy regarding the use of PSA (prostate-specific-antigen) in early detections of prostate cancer continues with the recent publication of an article in the New England Journal of Medicine (NEJM).

Prostate cancer is the most frequent cancer and the second leading cause of death from cancer in men, exceeded only by lung cancer. In 2008, an estimated 24,700 men were diagnosed with prostate cancer and 4,300 died of the disease.

The walnut size prostate gland lies below the urinary bladder in front of the lowest inch of the rectum, through which it can readily be felt on digital rectal examination (DRE). The gland has an important role in the proper flow of urine. It also provides the proteins and ions that form the bulk of the semen. In conjunction with other smaller glands in the vicinity, the prostate gland produces secretions that serve to lubricate the reproductive system and provide a vehicle for storage and passage of sperms.

Once upon a time, “the old finger” i.e. DRE was the only crude way to pick up early prostate cancer. Although DRE has a cancer detection rate of only 0.8 to 7.2 percent, it remains an important test that can be done easily in a doctor’s office. It also checks for anal and rectal tumours.

The PSA test was introduced in North American medical practice by the end of 1980s. PSA was expected to replace the embarrassing and uncomfortable DRE. And it was promoted as an ideal test for screening and early detection of prostate cancer. But this hope has not materialized. PSA blood test has a false positive rate of 20 to 50 percent and false negative rate of 25 to 45 percent. That means 30 to 50 percent of the time the test is wrong.

The editorial in the NEJM says, “In the United States, most men over the age of 50 years have had a prostate-specific–antigen (PSA) test, despite the absence of evidence from large, randomized trials of a net benefit. Moreover, about 95 per cent of male urologists and 78 per cent of primary care physicians who are 50 years of age or older report that they have had a PSA test themselves, a finding that suggests they are practicing what they preach.”

Recent clinical trials have shown that PSA screening without DRE was associated with a 20 per cent relative reduction in the death rate from prostate cancer at a median follow-up of 9 years, with an absolute reduction of about 7 prostate cancer deaths per 10,000 men screened. Critics say that this is at best a modest effect on prostate cancer mortality and the benefit comes at the cost of substantial over-diagnosis and over-treatment. There is net harm compared with potential benefits.

Experts agree that PSA testing is an imperfect screening tool. They say the test is as effective as programs such as mammography for breast cancer and fecal occult blood testing for colorectal cancer.

The Canadian Cancer Society recommends that men aged 50 and older discuss the benefits and risks of PSA testing with their physician, and the society does not plan to change its recommendation based on recent research.

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Role of Calcium and Milk Products in Prostate Cancer

Dear Dr. B: We are in Arizona for the winter. My husband and I have always taken calcium and Vitamin D. There seems to be a lot of controversy here with several people who feel that calcium for men is putting them at high risk for prostate cancer.
Apparently this warning was on T.V. and in the newspapers. What is the truth, doctor?

Answer: Nobody knows exactly what causes prostate cancer. There are a variety of factors implicated in this process. There are some factors (diet and weight) you can change but others like age, ethnicity and family history cannot be changed.

As we know, prostate gland is present only in man. Any normal man can develop prostate cancer because normal men have male hormones (testosterone). Lack of testosterone due to any cause can reduce the risk of prostate cancer.

Age is an important factor. Prostate cancer is rare before the age of 45. As one gets older, the risk increases. Men of African or Caribbean ancestry have the highest risk.

What has race to do with prostate cancer? Scientists are not sure about that. There may be subtle genetic, dietary, environmental and hormonal differences. Another interesting fact is that dark skin absorbs less sunlight than light skin, which may contribute to the higher incidence of prostate cancer among men of African or Caribbean ancestry because of lack of vitamin D.

Family history is important. If your father or brother has had prostate cancer you are approximately two to two and half times more likely than the average man to be diagnosed with the disease during your lifetime. Having two first-degree relatives with prostate cancer increases your risk to about five to 10 times that of a man with no family history, and your risk soars to almost 100 per cent if three or more first-degree relatives have had prostate cancer.

Diet is linked to prostate cancer. A low fat diet may help prevent prostate cancer. Foods rich in saturated fats have been associated with increased risk of prostate cancer, possibly because they are metabolized into testosterone. Fish oils may protect against prostate cancer especially omega-3 fatty acids found in fatty fish like trout, anchovies, bluefish and white albacore tuna.

What about the role of milk, cheese and calcium? The American Cancer Society website article of 2001says, “Experts say excessive calcium intake may be unwise in light of recent studies showing that high amounts of the mineral may increase risk of prostate cancer.”

Here is a dilemma. There is a reasonable evidence to suggest that calcium may play an important role in the development of prostate cancer but evidence also shows calcium may lower the risk of colon cancer and age-related thinning of the bones.

The recommended daily allowance (RDA) of calcium is 1,000 mg per day for men and 1,500 mg for women. Important thing to remember is the words, “excessive calcium intake.” It is also critical to remember that this evidence is not conclusive. The word “may” is used quite often in this context.

You can have milk, cheese and other dairy products in moderation. An 8-ounce glass of milk contains about 300 mg of calcium, an ounce of cheese has about 200 mg, and a serving of yogurt has about 312 mg of calcium. Men should stay within 1000 mg of calcium per day. And don’t forget your vitamin D 1000 to 2000 IU per day especially in winter months. Vitamin D has an important role in preventing prostate cancer and other cancers.

A balanced diet, combined with regular exercise, is always a good idea.

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