NEWSLETTER September 2012

PREVENTIVE HEALTH – Screening for Colon Cancer

Colon cancer is the third leading cause of cancer in Western societies and in a number of these countries it is the second leading cause of death from cancer. Annual rates of colon cancer vary considerably from 47/100,000 in New Zealand to 4.1 /100,000 in South Central Asia. Rates for Western Europe and North America are approximately similar at 36/100,000. This wide variation is thought to be due to environmental factors, particularly diet.

There are approximately 50,000 deaths from colon cancer in the US each year, 17000 in the UK and 500,000 worldwide. These deaths represent a major failure of preventive health, as colon cancer is a preventable disease. If detected early, colon cancer can be cured by surgical removal of part of the affected bowel. In many cases this procedure can performed using laparoscopy (keyhole surgery).
There are a number of screening tests available for colon cancer, including the following;

Faecal Occult Blood Test (FOBT). This test detects the presence of blood in stoo samples. The older chemical or guaiac test is affected by animal blood from red meat and other dietary factors. The newer immunochemical tests detect only human haemoglobin and are not affected by diet. They are also more sensitive than the guiac test. A positive test will usually require further investigation using colonoscopy. These tests have a low detection rate for early stage growths (polyps), and will not detect all cancers.

Sigmoidoscopy. This involves examination of the rectum and the lower portion of the colon by insertion of a sigmoidoscope (a flexible optical tube with a light source). This procedure will detect pre-cancerous growths (polyps) and tumours, which may be removed or biopsied.

Colonoscopy. This procedure involves examination of the rectum and entire colon by insertion of a colonoscope (a flexible optical tube with a light source). This procedure may detect polyps or tumours in the rectum and entire length of the colon which may be removed or biopsied.

Double Contrast Barium Enema (DCBE). In this procedure the colon and rectum are outlined by the introduction of a mixture of air and barium, and a series of images created using x-rays. This technique is not as sensitive as colonoscopy for the detection of polyps and tumours.

FOBT, sigmoidoscopy and colonoscopy have all been shown to improve the early detection of some polyps and cancers and to reduce mortality, however none of these tests has a high degree of sensitivity or specificity, and the search for improved screening tests continues. This has resulted in the introduction of some new screening tests, particularly

Virtual Colonoscopy. This procedure involves a CT scan of the colon after it has been distended by the introduction of air. This computerised tomographic colonograph produces a 3 dimensional image of the colon which can be examined for polyps or tumours. It is a less invasive procedure than standard colonoscopy, however any abnormalities detected will often require further investigation using routine colonoscopy. Studies are continuing to determine whether virtual colonoscopy is an effective screening test fro colon cancer
Stool DNA test. This test uses specialised amplification and detection techniques to identify abnormal DNA from tumour cells that are shed in stool samples. Early studies indicate that this test may be more sensitive and specific than occult blood tests, however insufficient information is currently available to determine the screening efficacy of this test.

To Screen or Not to Screen

Current evidence is significantly in favour of screening. The American cancer Society currently recommends screening using one of the following 5 options

Yearly stool tests for blood

Sigmoidoscopy every 5 years

Yearly stool tests for blood and sigmoidoscopy every 5 years

Double Contrast Barium Enema every five years

Colonoscopy every 10 years

Recent publications have suggested that option 3, using an immunochemical occult blood test may be the most effective screening procedure

Advantages of Screening

Effective screening increases the chances of early detection of polyps or tumours and facilitates there removal, which may take place during the screening process. Surgery for the removal of early tumours, if required, is a relatively simple procedure with a high cure rate.

Effective screening has been shown to significantly decrease the morbidity and mortality from colorectal cancer

Disadvantages of Screening

Current screening methods will not detect all cancers and false positive faecal occult blood tests cab result in unnecessary colonoscopies.
Fasting and the use of bowel cleansing preparations are required for sigmoidoscopy and colonoscopy
There is a minor risk of tears or abrasions to the colon during sigmoidoscopy
The use of sedation during colonoscopy may be hazardous to some patients

Approximately 80% of bowel cancers occur in individuals who are over 60, however current recommendations suggest that screening should commence at 50 years. In individuals who have a family history of disease or a genetic predisposition, screening may be advisable at an earlier age

For further information see Colon Cancer in disease list

DID YOU KNOW – There is more to calcium than bones

When most people think of calcium they think of bones, where 99% of the body’s calcium is stored in the form of hydroxyapatite. However calcium is much more than a building block for the skeleton. Calcium is one of the most important elements in a number of physiological processes, including nerve conduction, muscle contraction and relaxation, endocrine hormone secretion and cell membrane function.

Calcium is absorbed from food in the intestine, excreted by the kidneys and stored in bones. Levels of calcium are tightly controlled by parathyroid hormone, calcitonin, oestradiol and vitamin D, which work together to control the absorption of calcium from the digestive system and the absorption and release of calcium from bones.

Vitamin D stimulates intestinal absorption of calcium and regulates parathyroid hormone release.

Control mechanism for calcium

Most of the body’s vitamin D is manufactured in the skin by the action of ultraviolet light (sunlight). Individuals who live in areas with limited sunlight are at risk of vitamin D deficiency, which will affect the absorption of calcium by the digestive system. Vitamin D deficiency is relatively common in older individuals and in those suffering from malabsorption syndromes, intestinal disease such as celiac or pancreatitis. A diet deficient in calcium may also result in decreased blood levels of calcium.

Some medications, particularly steroids, may inhibit calcium absorption

Patients with hypocalcaemia (low calcium levels ) are often asymptomatic, however some individuals may experience muscle spasm or cramps, or numbness or tingling in the fingers or toes. Hypocalcaemia may also result in coarse hair, brittle nails and dry skin.

Low calcium levels may result in high bone turnover and osteoporosis in older individuals and bone deformities (rickets) in young children.

For further information see Hyperparathyroidism in disease list

NEWS – Low levels of vitamin D linked to asthma

Research at the Children’s National Medical centre in the USA has shown a strong link between low vitamin D levels and asthma. Researchers compared vitamin D levels in a group of African American children with asthma with a set of non-asthmatic healthy controls. The study revealed that 86% of the asthmatic children were vitamin D deficient compared with 19% of the non-asthmatic controls.

It has been postulated that the low vitamin D levels may cause hypocalaemia (low calcium levels) which can cause involuntary muscle contraction including bronchospasm.

Vitamin D deficiency is known to affect bone growth and density, however this study adds to the growing evidence linking vitamin D deficiency to other conditions such as depression and autoimmune disorders.

For further information see Asthma in the disease list