Study Found that Cigarette Smoking May Increase the Risk of Colorectal Cancer Incidence In a Japanese Population

A study conducted by researchers in Japan found that cigarette smoking may increase the risk of colorectal cancer (CRC) incidence in a Japanese population While smoking has been associated with an increased risk of CRC among Western populations, it has not been investigated as a risk factor in Asian populations prior to this study, according to the authors.

Statistics show that 60% of CRC cases occur in developed countries and CRC incidence continues to increase rapidly in Asia. Specifically, Japan experienced an increase in cases from 1978 to 1993 and has remained stable since then but is still among the top 10 countries with the highest incidence of CRC. A separate Japanese study found a gender-based difference in CRC incidence, with men being more susceptible to rectal cancer and women being more susceptible to colon cancer:

Colon cancer:

• Men: 65.7%
• Women: 75.4%

Rectal cancer:

• Men: 34.3%
• Women: 27.0%

It is hypothesized that environmental and lifestyle factors, such as smoking, can increase the risk of CRC. In Japan, for instance, 80% of men and 20% of women were smokers in the 1950s. However, a significant reduction was observed in smoking rates by 2017: only 32% of men and 9% of women were smokers. The age-standardized CRC incidence rate was 22.2 in 1978 and 38.9 in 2018.

Tobacco use can cause many different cancers, including mouth, larynx, lung, kidney, liver, and many more . In 2014, the U.S. Surgeon General’s report added CRC to the list of tobacco-related cancers. However, there are some issues with this:

• Evidence supporting the claim that the use of tobacco is associated with the development of colon cancer has been derived mainly from Western populations while data from Asian populations are conflicting. More research is needed on this association in Asian populations.
• Meta-analysis by geographic region did not find a significant association between smoking and CRC in Asian studies

The Japanese study aimed to investigate the correlation of smoking and CRC incidence in Asian populations.

Researchers used original data from major cohort studies performed by the Research Group for the Development and Evaluation of Cancer Prevention Strategies in Japan. The following criteria  were used when examining these studies for this analysis:

• Population-based cohort studies conducted in Japan
• Studies initiated between the mid-1980s and mid-1990s
• Studies with more than 30,000 participants
• Studies that acquired information on health-related lifestyles
• Studies that followed the incidence of CRC

A self-administered questionnaire at the baseline survey determined if each participant was a smoker and classified them into one of three groups: never smoker, former smoker, or current smoker. Participants were followed-up for CRC incidence from the baseline study until the date of CRC diagnosis, migration out of the study area, death or the end of follow-up, whichever was first. The end of the follow-up period was between December 31, 1992 and December 31, 2014.

The study found that men who were ever, current or former smokers had a statistically significant higher risk of CRC than never smokers. Ever and current smoking increased the risk of both colon and rectal cancer, while former smokers had an increased risk of colon cancer.

Women who were ever, current or former smokers did not have an increased risk of CRC, but a significantly greater risk of distal colon cancer. Women who were heavily exposed to smoking had an increased risk of CRC.

Colon cancer is one of the most preventable diseases through screening methods and avoiding risk factors such as smoking , obesity, and poor diet. The American Cancer Society recommends getting screened at age 45 or younger if you have a family history of CRC.