Thursday, April 28, 2011

Colorectal Cancer, which screening test is best?

Colorectal cancer (CRC) is the second leading cancer killer in the U.S. That is an alarming statistic, considering that, for the most part, CRC is a preventable disease. CRC usually begins as benign growths called polyps in the colon or rectum, and removing these growths effectively eliminates the possibility that they will develop into cancer.

The importance of early detection is underscored by these statistics from the American Gastroenterological Association:
  • When CRC is diagnosed at the early localized stage, the five-year survival rate is 90 percent.

  • When CRC is not diagnosed until the late distant stage, the five-year survival rate is only 10 percent.
There are a number of ways to screen for CRC. The two main types of tests are: 1) those that look for signs of colon cancer from the stool, and 2) those that visually inspect the colon looking for pre-malignant lesions such as polyps.

Stool Tests for CRC:
  • CalorieFecal occult blood test(FOBT). This is the most common type of stool test, often known by its commercial name "Hemoccult". The FOBT is used to find hidden (occult) blood in feces coming from damaged blood vessels on the surface of polyps or colon cancers. Only rarely is there enough bleeding to be visible in the stool, but by placing a special chemical (guaiac) on a small sample of stool, the presence of blood can be detected. To be most accurate, the FOBT should be done on several stool samples on an annual basis.

  • Fecal immunochemical test (FIT). The FIT is a newer kind of test that also detects occult blood in the stool. This test reacts to part of the human hemoglobin protein, which is found in red blood cells. It is recommended that this test be done on an annual basis.

  • Stool DNA test (sDNA). This is the newest of the stool tests and has not yet gained wide acceptance. Its works by detecting DNA markers (genetic changes) that are common to colon cancer or precancerous polyps from a stool specimen. Barriers to the use of the stool DNA test include its high rate of false positives (a positive test for cancer when no cancer is present) and expense.
All of the stool tests for CRC have several serious drawbacks. First, if a positive stool test is detected, a follow-up test, such as a colonoscopy will need to be performed to determine why the test was abnormal. Secondly, blood in the stool can be a sign of colon cancer, but it is more often caused by something else, such as hemorrhoids, ulcers, or taking aspirin. These other conditions can cause a "positive" result even when you don't have cancer. In addition, stool tests may only become positive after CRC has developed. They are not as good at picking up premalignant lesions (e.g. polyps).

Tests that visually inspect the colon:
  • Sigmoidoscopy. A sigmoidoscope is a flexible, tube-like instrument with a light and a lens for viewing the walls of the colon. This instrument is approximately 2 feet long, which only allows it to inspect the rectum and lower portion of the colon. Some physicians who perform sigmoidoscopy are able to remove polyps or tissue samples during this procedure, which can then be checked by a Pathologist for signs of cancer.

  • Colonoscopy. This test is similar to sigmoidoscopy although the instrument is longer and able to view the entire colon. Biopsies or removal of polyps can be performed at the time of the study.

  • CalorieCT colonography (virtual colonoscopy). This is a special type of x-ray test that uses a computer program to create a 3-dimensional picture of the lining of the colon. If detected during this procedure, however, the polyps or cancer cannot be biopsied or removed. A second procedure (usually a colonoscopy) must be performed to have this done.

  • Air contrast barium enema. The air-contrast barium enema is a type of x-ray test that was used for years before sigmoidoscopy or colonoscopy were in widespread use. In performing this test, a chalky liquid called barium sulfate is introduced into the colon and x-rays are performed. If suspicious areas are seen on this test, a colonoscopy will be needed to explore them further.
Screening recommendations: According to the American Cancer Society, if everyone were screened for CRC, tens of thousands of lives could be saved each year. Screening recommendation, however, vary among experts. The U.S. Preventive Services Taskforce (USPSTF) recommends screening for colorectal cancer in adults aged 50 to 75 years using FOBT (annually), sigmoidoscopy (every 5 years), or colonoscopy (every 10 years). They do not recommend screening after the age of 75 since the development of colon cancer from a polyp is so slow. The USPSTF does not support the use of computed CT colonography or fecal DNA testing to screen for CRC at this time. The American Cancer Society, the U.S.Task Force on Colorectal Cancer, and the American College of Radiology recommend screening for colorectal cancer beginning at 50 years of age by 1) FOBT or FIT testing annually, 2) flexible sigmoidoscopy every 5 years, 3) double-contrast barium enema every 5 years, 4) CT colonography (virtual colonoscopy) every 5 years, or 5) colonoscopy every 10 years. With few exceptions, authorities agree that of all the screening tests available, colonoscopy is considered the "gold standard" against which the others can be compared.

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Thursday, April 21, 2011

How Accurate Are Devices That Track Calories Burned?

CalorieWhen accuracy is highly important in determining the number of calories burned with specific activities, a laboratory-based test called indirect calorimetry is often used. This test estimates the amount of heat produced (calories) by measuring the differences in oxygen and carbon dioxide in inspired and expired air. Obviously, this type of testing would be impractical for people to use in a free-living situation. To address this need, a number of devices are available for estimating caloric expenditure during exercise, including heart rate monitors, pedometers, and accelerometer-based activity monitors. While none of them are as accurate as calorimetry for measuring calories burned, each has its own advantages and disadvantages. To a large degree, the device that is best for a particular individual depends on one's budget and preferred type of exercise.

PedometerThe word pedometer literally means, "counting footsteps". This count is converted into distance by knowing the length of your usual stride. The number of calories that you have burned is estimated from the distance that you have walked. For example, a brisk walk for an average 200-pound adult burns about 100 calories per mile. To get an estimate of the calories burned while walking, the number of miles walked is multiplied by 100. A drawback of the pedometer is that body weight and intensity of walking, important determinants of calories burned, are not taken into consideration. Additionally, pedometers are unable to provide meaningful caloric information related to activities involving "resistance" such a bicycling or weight lifting. Pedometers are the least expensive of the devices used to estimate calories burned and can be perfectly adequate if walking or jogging is the primary form of exercise. A popular campaign, the "10,000 step programs", uses a pedometer to help people achieve the goal of walking 5 miles each day, consuming approximately 500 calories in the process. Heart rate monitors typically consist of a chest belt that transmits heart rate
information to a wrist-worn display.

Heart rate monitors are commonly used by competitive athletes to assist with their training programs, but certain ones can also provide information on caloric expenditure. Polar, a manufacturer of heart rate monitors, developed a feature known as OwnCal that uses personal information (body weight, height, age, etc.), along with heart rate information to calculate the number of calories burned. Unfortunately, the formulas that most heart rate monitors use to measure calories burned have not been compared with more accurate methods, such as indirect calorimetry. Another shortcoming of heart rate monitors is that they are not useful for tracking caloric consumption during activities that do not cause the heart rate to increase, such as many activities of daily living. Additionally, heart rate can be elevated by nervousness or dehydration, leading to inaccurate results. A heart rate monitor could be particularly useful, however, for someone who swims for exercise, since special water resistant models are available.

The most accurate of the commercially available devices to measure caloric consumption utilize an instrument called an accelerometer. Two examples of this type of calorie counter are the bodybugg Calorie Management System and the BodyMedia FIT (also known as the SenseWear System). The bodybugg has gained recognition by being used by contestants on the reality TV show, "The Biggest Loser". Accelerometers are usually worn around the arm and measure the motion of the body in several planes. In addition to measuring movements, both of these products measure skin temperature,heat fluxPedometer (the amount of heat leaving the body), and galvanic skin response -- a measure of electrical conductivity that changes when you sweat. The device uses all of this information to calculate caloric consumption. Products using accelerometers are the most expensive of devices used to measure caloric consumption but have been well studied scientifically and found to have an acceptably small margin of error (from 2.5% to 10% in clinical studies). Some manufacturers of these products also provide a subscription service that allows you to download your activity information and compare with your food intake.

While none of these devices is capable of determining the exact number of calories burned during various activities, they can encourage regular exercise and be a good motivator for sticking with a weight loss program.

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Friday, April 15, 2011

Jet Lag

SleeperAnyone traveling by rapid transit to more distant locations can be affected by jet lag. Known in medical jargon as desynchronosis, jet lag is caused by the body's internal clock having to be reset to a new time zone. It is typically worse for travelers crossing three or more time zones. Although considered a sleep disorder, jet lag can develop in someone who ordinarily does not suffer from insomnia or other sleep disturbance when at home.

Features of jet lag. Jet lag most commonly affects sleep patterns. When considering the time of day at the destination, people traveling to the east will become sleepy later than usual and those traveling west, will awaken earlier. Until adjustment to the new time zone occurs, jet lag can adversely affect performance in both physical and mental tasks. Other features of jet lag include irritability, fatigue, and difficulty concentrating. Certain symptoms that are sometimes attributed to jet lag, such as foot swelling, earache, and dry eyes, are more likely related to the mode of travel, such as the cramped seating and low humidity inside an airplane cabin.

Why jet lag occurs. A structure in the brain called the hypothalamus governs a number of body functions, including sleep. It serves as an internal clock to help tell the body the time of day. Light sensing nerves from the eye inform the hypothalamus of when it is dark or light outside. In response to signals from the hypothalamus, a small gland known as the pineal body produces more or less of a hormone known as melatonin. When the pineal body gets the message that the sun has set, more melatonin is produced, which causes us to become sleepy. When the sun comes up, the pineal gland stops producing melatonin, encouraging us to wake up. Jet lag occurs because of a delay in the hypothalamus adjusting to the light/dark cycles of a new environment.

Fruits and VegetablesCan jet lag be prevented? With long journeys that cross a number of time zones, some degree of jet lag is inevitable. Nevertheless, there are certain measures that may help to prevent or shorten the period of time that jet lag symptoms occur. Measures that may help include:
  • Get plenty of sleep prior to travelling so that your body is rested and better able to tolerate travel-related stress.

  • Begin adjusting your body to the new time zone before you leave. For example, if you are traveling from west coast to east coast, set your daily routine back an hour or so a couple of weeks before departure. Then, set it back another hour the week prior to leaving. This will help ease the adjustment to a new time zone.

  • Drink plenty of water, particularly when traveling by air to help counteract the dry environment of the plane.

  • Avoid drinking alcohol or caffeinated beverages, which can have an adverse effect on sleep quality.

  • Consider breaking up the journey up with a stopover to ease into the time change.

  • On arrival at the destination, begin adapting to the local schedule (eating, sleeping, etc.) as soon as possible.
Are medications available for treating jet lag? The American Academy of Sleep Medicine (AASD) supports the short-term use of hypnotics (sleep medications) for jet lag-induced insomnia. Specific sleep medications that have been shown to be effective include zolpidem (Ambien) and temazepam (Restoril). Although controversial, some clinicians advocate the use of 0.5 mg to 5 mg of melatonin during the first few days of travel. Several studies have demonstrated that melatonin can help with jet lag by reducing the number of days required to establish a normal sleep pattern, improving alertness, and reducing daytime sleepiness. As a nutritional supplement, however, some concern exists regarding the purity of melatonin since the Food and Drug Administration does not regulate its production. Additionally, there are a number of potential medication interactions with melatonin. Anyone taking prescription medications should check with their doctor to make sure that it is safe to take melatonin along with their regular medications.

How long does it take to get over jet lag? This varies depending on the individual, the direction of travel, and the number of time zones crossed. Some people may not be bothered at all, particularly when crossing only one or two times zones. Crossing more time zones or traveling eastward generally increases the time required for adaptation. As a rule, when traveling in an eastward direction, the number of days that sleep will be disrupted is equal to two thirds of the number of time zones crossed. For example, if six time zones are crossed, it may take up to 4 days for the body to become adjusted to the new time zone. Slightly less time is required for adjustment when traveling to the west.

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Monday, April 11, 2011

What causes congestive heart failure?

The recent death of actress Elizabeth Taylor from congestive heart failure (CHF) has generated a great deal of interest about this condition and its causes. Congestive heart failure is more common than many people realize, currently affecting nearly 5 million Americans, with around 550,000 new cases being diagnosed each year. In fact, for individuals older than 65 years, heart failure is the most common cause of hospitalization.

What happens to the body with heart failure? "Heart failure" does not mean that the heart has stopped working; rather, it means that the heart's pumping power is weaker than normal. To compensate, the main pumping chambers (ventricles) of the heart dilate allowing them to pump more blood. Eventually, the heart muscle thickens (hypertrophy) and the heart rate increases in an effort to maintain normal blood flow. Increased pressure in the heart causes blood to back up into other areas of the body, including the lungs, lower legs and liver. This results in fluid passing from the blood stream into these organs and the extremities. Heart failure also affects the kidney's ability to dispose of sodium and water, further contributing to fluid overload.

What Are the Symptoms of Heart Failure?
Symptoms of CHF vary, depending on whether the left or right side of the heart is primarily involved. With left sided heart failure, blood and fluid back up into the lungs causing shortness of breath, difficulty breathing when lying flat, and fatigue. With predominant right sided failure, blood and fluid back up causing swelling in the abdomen (ascites) and in the legs and feet (edema). Sometimes the heart failure affects both chambers of the heart with a blend of these symptoms. Other symptoms of CHF include rapid heartbeat, exercise intolerance, weight gain and persistent cough or wheezing with white or pink-tinged phlegm.

What causes Congestive Heart Failure?
The most common reasons for developingCHF are:

  • Coronary artery disease and heart attack. The buildup of fatty deposits in the heart's arteries (athlerosclerosis) causes the arteries that supply the heart to become narrowed. With severe narrowing, less blood reaches the heart muscle and the heart becomes starved for oxygen and nutrients. If the blood flow is completely blocked, a heart attack can occur. In a heart attack, a portion of the heart muscle dies, with the development of "scar tissue". This damaged area of heart tissue weakens the heart's ability to pump blood, leading to CHF.

  • High blood pressure. With untreated or poorly controlled hypertension (high blood pressure), the heart has to pump harder than normal to keep blood circulating. In order to compensate for the extra workload, the heart muscle becomes thicker. Over time, the enlarged heart becomes stiff and weak and is unable to pump blood effectively. Uncontrolled high blood pressure increases the risk of developing heart failure by two to three times.

  • Disease or deformity of the heart valves. Heart valves open and close with each heart beat to keep blood following in the proper direction. When the valves do not function normally, the heart muscle has to pump harder to keep the blood flowing as it should. Heart valve damage can occur due to a heart attack, infection (endocarditis), or can be due to a birth defect. Eventually, the extra workload created by a damaged valve weakens the heart. If the workload becomes too great, heart failure can result.

  • Heart muscle disease (cardiomyopathy). There are a number of causes for heart muscle disease including infections (e.g. viral myocarditis), alcohol abuse, and the toxic effect of certain medications including chemotherapy drugs.

  • Congenital heart defects. These are problems affecting the heart's chambers or valves that are present at birth. If the heart and its chambers don't form correctly, the healthy parts have to work harder, which in turn may lead to heart failure.

  • Abnormal heart rhythms (heart arrhythmias). A common arrhythmia that leads to the development of CHF is atrial fibrillation. The rapid, irregular heartbeat associated with this arrhythmia creates extra work for the heart that can lead to heart failure.
To some degree, congestive heart failure is a preventable disease. The best way is through lifestyle measures to avoid the development of coronary heart disease or hypertension. These measures include maintaining a healthy weight, keeping your blood pressure under control, eating a heart-healthy diet, staying physically active, and not smoking. If you already have one of the underlying causes, such as high blood pressure, adequate treatment will reduce the risk that congestive heart failure will develop.

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Friday, April 1, 2011

Antioxidants, Part 2 - What are the best sources of antioxidants?

Fruits and VegetablesTaking antioxidants is claimed to provide a number of potential health benefit By neutralizing free radicals, antioxidants, such as vitamins C and E, beta-carotene, lycopene and lutein may play a role in preventing diseases such as cancer, cardiovascular disease, and Alzheimer's disease. Conclusive research demonstrating their benefits, however, is lacking.

One possible explanation for this is that most research conducted to evaluate the benefits of antioxidants has used supplements, such as vitamin tablets, rather than dietary sources of antioxidants. In fact, even though most antioxidant supplements are generally safe, some research has found that taking high dosages of certain ones, such as vitamin E, can actually be harmful.

One of the primary reasons that dietary sources appear to be a better way of getting antioxidants than supplements has to do with the array of antioxidants contained in foods. While a supplement may contain only one type of antioxidant, certain foods can contain hundreds. It appears likely that the benefits of antioxidants are best provided through the complex combinations that are present in the foods we eat.

Which foods are rich in antioxidants? Antioxidants are abundant in fruits and vegetables, as well as in other foods including nuts, grains, and some meats, poultry, and fish. The list below includes several important antioxidants and their most common food sources:

  • Beta-carotene is found in abundance in foods that are orange or red in color, such as sweet potatoes, pumpkin, carrots, apricots, cantaloupe, and squash. Dark green vegetables including broccoli, spinach and kale are also excellent sources.

  • Vitamin C, also called ascorbic acid, is contained in citrus fruits and juices, tomatoes, dark green vegetables, red and yellow peppers, and in berries. Vitamin C is also found in cereals, beef, poultry, and fish.

  • Vitamin E, or alpha-tocopherol, is found in vegetable oils such as olive, soybean, corn, cottonseed and safflower, nuts and nut butters, seeds, whole grains, wheat, wheat germ, brown rice, oatmeal, soybeans, sweet potatoes, and legumes (beans, lentils, split peas).

  • Lycopene is most commonly obtained by eating tomatoes and tomato products. Other sources of this important antioxidant come from watermelon, pink grapefruit, and blood oranges.

  • Lutein is one of 600 known naturally occurring carotenoids. It is thought to play a particularly important role in keeping the eyes safe from free radical-induced damage. Lutein is especially abundant in green, leafy vegetables, such as spinach and kale.

  • Selenium, while not technically an antioxidant, is a component of several important antioxidant enzymes. Good food sources of selenium include crab, liver, fish, poultry, and wheat.

  • Vitamin A rich foods include liver, sweet potatoes, carrots, pumpkin, broccoli, and butter.
Foods that are high in antioxidants offer a number of health benefits. In addition to the free-radical neutralizing effects of antioxidants, many of these are plant-based with the added benefits of being lower in fat with a high fiber content. While the American Heart Association does not recommend using antioxidant vitamin supplements until more complete data are available, it does recommend that people eat a variety of nutrient-rich foods daily from all the basic food groups.

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