Lifestyle factors and cancer risk: a review of recent research

Lifestyle Factors Inducing Cancers

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Cancer is one of the leading international causes of morbidity and mortality. Lifestyle factors that contribute to causing cancer have been widely studied in recent years. Summarizing relevant studies, lifestyle factors identified include smoking, alcohol consumption, diet, weight management, physical activity, and environmental exposure. These studies use a variety of methodologies to determine the link between the lifestyle factor and risk of cancer. Issues with the methods of these studies can be addressed by future research that attempts to remedy methodological defects while replicating results. Valid and reliable information is essential to using information about lifestyle factors to combat cancer.

Lifestyle Factors Inducing Cancers

As one of the leading causes of mortality in the world, it is estimated that cancers will have killed 10 million people around the globe by 2020 (Haque et al. 2010). In 2009, the American Cancer Society estimated that there were nearly 1.5 million new cancer cases and about 560,000 cancer deaths (Khan, Afaq, and Mukhtar, 2010). Unfortunately, there is no guaranteed form of treatment for cancer and emphasis has been placed on prevention and early detection in order to combat this disease (Haque et al., 2010).

While the precise etiology of the disease is unknown, a number of causes of cancer have been identified and different factors can increase or reduce the risk of developing cancer (Haque et al., 2010). Genetics may predispose an individual to develop cancer or put them at a higher risk for a certain type of cancer because of a mutation at a certain codon (Naguib et al., 2010). Additionally, exposure to certain carcinogens or infections may increase the risk of developing a related type of cancer (Yamaji et al., 2009). Lifestyle factors build on the predetermined risk that comes with one's genetics and can induce cancer (Haque et al., 2010).

With 10 to 70% of cancer mortality being attributable to lifestyle factors (Haque et al., 2010), this article will review studies from the last five years addressing the impact of lifestyle factors on inducing cancer. This author will critique the studies, discussing the strengths and weaknesses of the methodology. Finally, the paper will conclude with recommendations for future research.

Studies on the Correlation of Lifestyle and Cancer

Numerous studies have considered the impact of lifestyle factors such as smoking habits and physical activity levels on cancer. This section discusses the findings of those studies with respect to each lifestyle factor. Many studies consider the same factors, but focus on different types of cancers. Within the discussion of each lifestyle factors, the differing impact on specific cancers may be noted.

Smoking

Smoking is one of the more well-known lifestyle factors that contribute to the incidence of cancer. It is estimated that smoking cigarettes causes 85 to 90% of lung cancers and long-term smoking leads to an increase in the risk for colon cancer (Khan et al., 2010). Active and passive smoking can lead to the production of Polycyclic Aromatic Hydrocarbons, or PAH, which are established carcinogens that target the following body organs: lungs, breasts, oropharynx, genitourinary tract, and gastrointenstinal tract (Haque et al., 2010).

Khan et al. (2010), used an article review to identify studies of the link between lifestyle factors and cancer. The studies cited by the authors found no significant sex differences in the carcinogenic effects of smoking. The authors explained that intensity and duration of smoking are critical with the largest risks for those that were between 20 and 22 years of age when they started smoking and those that smoke 20 to 29 cigarettes per day. The literature review also noted that current smokers have a higher rate of lung cancer death than do former smokers (Khan et al., 2010).

Boniol and Autier (2010) examined the correlation of cancer and lifestyle risk factors in Europe by looking at the pattern of cancer incidence and data on lifestyle factors. The rate of cancer correlated with smoking rates. For example, in countries where smoking cessation programs had not begun and there were fewer former smokers, there continued to be increases in the incidence rates of cancers in the respiratory tract. This was seen primarily in Eastern European countries. (Boniol and Autier, 2010)

Bissonauth et al. (2009) examined the link between smoking and breast cancer, focusing on female French-Canadians. The researchers were testing the effect of lifestyle factors while controlling for the common BRCA mutations by using equal numbers of carriers the frequent mutations and non-carriers. They found that those who smoked cigarettes for greater than 9 pack-years had a 59% higher risk of breast cancer. When the results were split by premenopausal and postmenopausal women, they found that premenopausal smokers had a 63% increased risk and there was a 49% higher risk for postmenopausal smokers. (Bissonauth et al., 2009)

Yamaji et al. (2009) examined Japanese subjects for the effect of smoking on gastric cancer. In this study, the researchers identified lifestyle factors and evaluated their independent effect on gastric cancer incidence.

Alcohol Consumption

Drinking alcohol has also been identified as a lifestyle risk factor for cancer and excessive drinking may cause or increase the risk of liver, pharynx, larynx, oral, esophageal, colorectal, and breast cancers (Haque et al., 2010). According to the U.S. Department of Health and Human Services' National Toxicology Program (2005), alcohol consumption is considered to be a known carcinogen because the peripheral lymphocytes of alcoholics show more frequent chromosomal aberrations, aneuploidies, and sister chromatid exchanges. Drinking potentiates the detrimental effects of smoking tobacco, making simultaneous alcohol consumption and smoking especially dangerous for the development of cancer (Haque et al., 2010).

Khan et al. (2010) also reviewed studies linking alcohol consumption to breast, lung, and colon cancer. A cohort study found that binge drinking led to a 55% increased risk in breast cancer and regular, moderate drinking also increases risk for breast cancer. For lung cancer, increased risk was associated with high consumption of alcohol and consumption of hard liquors. There was no significant association for light and moderate drinking. Finally, daily consumption of three or more drinks was linked to increased risk of colorectal cancer and consumption of seven or more drinks per week increases the risk of colorectal cancers by 72%. One-fourth of colorectal cancer cases can be attributed to alcohol intake. (Khan et al., 2010).

Boniol and Autier (2010) also examined the pattern of alcohol consumption in Europe as compared to the incidence of cancer. Alcohol consumption matched the pattern of cancer incidence, with higher drinking rates in Eastern Europe and higher female consumption of alcoholic beverages in Ireland and Luxembourg. Slovakia and Hungary, countries with high rates of both alcohol consumption and smoking, had a higher incidence and death rate of oral and pharyngeal cancers. (Boniol and Autier, 2010)

Yamaji et al. (2009) considered the impact of alcohol consumption on gastric cancer as an independent risk factor for developing cancer. They found that non-regular drinkers had a 0.06% rate of developing gastric cancer and the rate of gastric cancer incidence in regular drinkers was significantly higher, at more than triple the rate of incidence for non-regular drinkers. (Yamaji et al., 2009)

Diet

Diet can both increase and decrease one's risk for various types of cancer. Habits associated with a good or bad diet may correlate with habits regarding physical activity and weight management. However, there are studies that attempt to separate the effects of diet on cancer incidence, which are discussed below.

Khan et al. (2010) found that high fat consumption led to increased risk of breast, prostate, lung, and colorectal cancers. Saturated fat, in particular, was linked with breast cancer. Animal fat, in particular, was linked with prostate cancer. Fat from red and fried meats was linked with lung cancer. Consumption of high-fat dairy products and processed meat was linked with colon cancer incidence. On the other hand, the authors noted studies demonstrating that increasing one's consumption of fruits and vegetables could help decrease the risk of cancer. (Khan et al., 2010)

Naguib et al. (2010) examined dietary lifestyle factors and their correlations with BRAF and K-ras mutations. There were few significant results in the relationship between diet and mutations. Higher white meat consumption was linked with a higher K-ras mutation rate. Similarly, lower fruit consumption was also linked with higher rates of K-ras mutation. (Naguib et al., 2010)

Boniol and Autier (2010) examined the rates of fruit and vegetable consumption to compare to cancer incidence patterns in Europe. The researchers found some indication that lower rates of consumption of fruits and vegetables were linked with higher rates of cancer in those countries. However, the researchers did not emphasize these results as the sources of data were too heterogeneous to compare and remain within the bounds of sound statistical analysis. (Boniol and Autier, 2010)

Haque et al. (2010) did not focus on increasing rates of cancer, but focused on the preventative characteristics of dietary phytochemicals. The authors noted that certain items added to a diet will increase blocking agents that can prevent carcinogens from reaching targets and increase suppressing agents that inhibit development of malignancies. The items and their chemopreventative phytochemicals (in parentheses) noted are turmeric (curcumin), honey (caffeic acid phenethyl ester), soybean (genistein), broccoli (sulphoraphane), ginger (gingerol), grapes (resveratrol), green tea (epigallo-catechin gallate), chilli peppers (capsaicin), cabbage (indole-3-carbinol), and strawberry (ellagic acid).

Physical Activity

Physical activity is correlated with diet and weight management by offsetting the negative effects of both. Its effects on the risk for cancer may be intrinsically bound up with these other elements as individuals may struggle with all three of these lifestyle factors at the same time. However, the studies examine physical activity's benefits in preventing cancer and the detrimental effects of not getting enough physical exercise.

Boniol and Autier (2010) examined the physical activity levels in European countries to compare to cancer incidence patterns across those countries. The researchers found some indication that increased levels of physical activity were linked with lower risks of developing cancer in those countries. However, the researchers noted that the data came from sources that were too different effectively compare and maintain statistical integrity. (Boniol and Autier, 2010)

De Vries et al. (2010) studied the effects of physical inactivity on cancer incidence. The authors found a negative correlation between the level of activity and the risk for cancer. They noted that the ideal scenario would involve participation in at least 30 minutes of moderate physical activity at least five days per week. If such levels of physical activity were maintained across the population, there would be long-term declines in the rate of cancer in Europe. For women, in particular, increased levels of physical activity served to prevent avoidable forms of cancer. (De Vries, 2010)

Bissounauth et al. (2009) focused on the impact of physical activity on breast cancer risk in French-Canadian women. These authors used a controlled study to determine the impact of lifestyle factors on non-carriers of common BRCA mutations. They found that moderate physical activity is negatively correlated with the risk for breast cancer. In other words, maintaining moderate levels of exercise can help protect a woman without a common BRCA mutation from developing breast cancer. (Bissonauth et al., 2009)

Environmental Exposure

Environmental exposures are not necessarily a lifestyle factor as one's environment is not entirely within his or her control. However, certain aspects of environmental exposure are controllable. For example, a person can control his or her own occupation. Also, to some degree, sunlight or UV exposure may also be controlled.

The National Toxicology Program (2005) has listed a number of environmental carcinogens including wood dust, coke oven emissions, and diesel exhaust particles that may have varying levels of exposure depending on one's occupation. Employment in a chemical field could increase exposure to chemical carcinogens (Haque et al., 2010). The National Toxicology Program is the primary resource for information regarding various known and suspected carcinogens. In order to include one of these as a lifestyle factor for inducing cancer, more information is needed regarding the individual's occupation. Otherwise, the link to cancer is not avoidable through a change in lifestyle.

Radiation exposure is a well-known environmental carcinogen. Khan et al. (2010) discussed research that indicated radiation exposure was linked with a higher rate of breast cancer incidence. Specifically, women that had had more frequent chest x-rays and, thus, been exposed to more radiation, had higher rates of breast cancer later in life. (Khan et al., 2010) While x-rays may be unavoidable as part of medical treatment, some radiation exposure may be minimized.

UV radiation exposure is one of the most well-known carcinogens. Haque et al. (2010) noted that UV exposure from sunlight can lead to Squamous Cell Carcinoma (SCC). Exposure to sunlight, especially without sunblock, is the main environmental cause for skin cancer (Haque et al., 2010). This lifestyle factor can be altered by avoiding activities that increase UV exposure such as tanning and outdoor sports that are not shaded.

Article Critique

Each of the articles provides a different means of analyzing the issue of lifestyle factors, but each also come with methodological difficulties. The research discussed in the review above will be analyzed in alphabetical order as some authors are relevant to more than one lifestyle factor. This section will also provide recommendations related to the findings of each of the articles as suggestions for future research in this area. Even the articles with methodological issues can be used as a foundation for future research.

Bissonauth et al.

Bissonauth et al. (2009) presented a sample size limitation. The findings cannot be generalized as it was limited to French-Canadian women. Further research would need to determine if the findings could be extended to more people. One benefit of the methodology of the study was the use of control groups to account for the influence of BRCA mutations on the prevalence of cancer.

Boniol and Autier

Boniol and Autier (2010) take on an ambitious goal of examining cancer patterns in comparison with several lifestyle goals across Europe. Unfortunately, using multiple countries' data may mean that the data sources is dissimilar and difficult to compare. As such, Boniol and Autier were unable to provide confident results on some lifestyle factors. However, their findings point future researchers in the direction of plausible lifestyle factors to study further and may demonstrate the validity of past public health initiatives aimed at certain lifestyle risk factors.

De Vries, et al.

De Vries et al. (2010) uses a hypothetical situation that involves ideal weight distribution across an entire population to extrapolate the benefits of such a change. While an interesting exercise that demonstrates the need for lifestyle changes, it is a hypothetical situation that is probably impossible to attain. There will always be those that are extremely overweight and underweight, preventing an ideal weight distribution. A discussion of the ideal situation is a good first step, but future research may work to evaluate the impact of realistic public health interventions.

Haque et al.

Haque et al. (2010) did not discuss the impact of the carcinogen blockers and suppressers found in common food items with relation to a specific population. The article was based on prior research of those chemopreventative phytochemicals. Future research may want to build on the discussion in this article and identify the effects of each of those on the risk for various cancers.

Hariss et al.

Harriss et al. (2009) performs a meta-analysis that uses a large amount of data. However the researchers did not collect the original data themselves. As such, this article cannot vouch for the validity and reliability of the data collection. Future researchers should collect their own data and determine if the findings of this article can be replicated.

Khan et al.

Khan et al. (2010) uses a review of other studies. While it does not attempt to rely on others' data, this article does not provide any unique findings of its own. It is a useful resource for synthesizing relevant material. Like the meta-analysis, additional research is needed to replicate the findings of the articles relied on by Khan et al. (2010) and the conclusions drawn by the authors.

Naguib et al.

Naguib et al. (2010) uses a limited sample from the EPIC Norfolk study. Additionally, its links are to mutations related to cancer, rather than the incidence of cancer itself. Future research should expand the sample size used and attempt to correlate the lifestyle factors with cancer incidence as opposed to a mutation that may lead to cancer. This will build on the findings Naguib et al. (2010), providing more applicable results.

Yamaji et al.

Yamaji et al. (2009) also has a limited sample size as its participants are from two medical centers in Japan. The authors even note Japanese cultural attributes that may have affected the outcome of the study (Yamaji et al., 2009). As such, future research is essential to determine if these findings can be replicated outside of Japan.

Recommendations and Conclusion

Future research is essential in this area. Identifying lifestyle factors that increase or decrease the risk for cancer will help provide individuals some control over the incidence of the disease. Larger and more diverse samples are needed to replicate these results. Methods such as cohort studies could determine the applicability of lifestyle factors identified here over a longer period of time with the same individuals.

In conclusion, a number of lifestyle factors impact the risk of cancer. These include smoking, alcohol consumption, diet, physical activity, weight management, and environmental exposure. Different factors impact certain cancers more than others. In order to combat cancer, the first step is to identify its causes. These studies and, hopefully, future studies are identifying causes and ways that individuals can combat cancer.