Obesity and junk food the culprits in increased bowel cancer rates in young adults

New research by scientists in the United States has found despite the overall declining rates of colorectal cancer among adults younger than age 50 years the rates are increasing.

An analysis of colorectal cancer trends by researchers at the American Cancer Society for the period between 1992 and 2005 has revealed that among young adults aged 20 to 49, incidence rates of the cancer increased 1.5% per year in men and 1.6% per year in women.

Overall incidence rates for colorectal cancer in the U.S. have been on the decline since the mid-1980s, accelerating in the most recent time period with rates now dropping by 2.8% per year in men and 2.2% per year in women, however the largest annual percent increase was in the youngest age group (20-29 years), in whom incidence rates rose by 5.2% per year in men and 5.6% per year in women.

The researchers led by Dr. Rebecca L. Siegel say the rises are due to an increase in left-sided tumours, particularly in the rectum, and more research is needed to clarify the causes for this trend and to identify potential prevention and early detection strategies - they suspect these increases may be related to rising rates of obesity and changes in dietary patterns, including increased consumption of fast food.

Increased screening and in particular colonoscopies among individuals ages 50 years and older has been responsible for the decline in colorectal cancer rates by detecting and removing polyps before they become cancerous, but routine screening is not recommended for adults younger than 50 years.

The researchers say obesity is a major risk factor for bowel cancer and dietary factors may also come into play - they say between the late 1970s and the mid-1990s, fast-food consumption in the U.S. increased 5 times among children and 3 times among adults.

A diet high in fast food is associated with both greater meat consumption and reduced milk consumption - increased consumption of red and processed meat has been shown to increase risk of cancers of the distal colon and rectum, while milk and calcium consumption have shown a protective effect against the subsites in which the rise in incidence was most prominent.

The researchers say it is possible that the emergence of unfavourable dietary patterns in children and young adults over the past three decades may have contributed to the increase in colorectal cancer rates among young adults and they suggest that the disparate increase in left-sided colorectal cancers warrants particular attention be given to studies to elucidate the behavioral and environmental risk factors responsible for this trend and potential prevention and early detection strategies.

The study appears in the June 2009 issue of Cancer Epidemiology Biomarkers and Prevention.