Exercise as it relates to Disease/Physical activities effect on the development of lung cancer

What study is being critiqued?

This is a critique of the research article ‘Physical activity and risk of lung cancer’ by I M Lee, H D Sesso and R S Paffenbarger (1999). The article discusses physical activities influence on developing lung cancer.

What is the background to this research?

Lung cancer is developed when abnormal cells grow and multiply in an uncontrollable manner in the lungs (3). The symptoms can develop from minor inconveniences such as shortness of breath and general weakness all the way to death (4). Lung cancer is the leading cause of cancer death in both Australia and the United States (2, 3).

A study by F.E. Speizer found that smoking is the most important risk factor in developing lung cancer in both men and women (5). This study also unveiled that healthier dietary choices will decrease the risk of lung cancer (5). The treatment for lung cancer is heavily dependent on how far the cancer cells have spread. Individuals with small cell lung cancer can be treated with surgery, chemotherapy, radiation therapy, targeted therapy (6).

Additional research has shown the benefits of physical activity and the role it plays in reducing the risk of developing lung cancer (7). It has also been found that varying intensities of physical activity help reduce the risk of lung cancer development (1, 7).

Where is the research from?

• This was an ongoing study conducted on men entering Harvard University as undergraduates between 1916 and 1950. Multiple health questionnaires were then periodically mailed to surviving alumni over the coming decades.
• All authors have an abundance of other research and are respected in their fields.

What kind of research was this?

• The research conducted was a prospect cohort study
• Participants who were identified as ‘similar’ were monitored over an extending period of time
• Prospect cohort studies have advantages such as elimination of recall bias. While also having disadvantages such as time and resource consuming. All of these factors need to be taken into consideration (9).

What did the research involve?

A potential 17,835 alumni (male undergraduates from Harvard University between 1916 and 1950) were identified after the initial health questionnaire in 1977. Although after the men with a history of cancer or who were not providing information on physical activity data were taken out, there were only 13,905 men successfully followed in this research.

These initial questionnaires asked men to estimate the amount of blocks they walked daily, flights of stairs climbed daily, and to list sports or recreation in which they participated in the last year (frequency and duration information acquired). Using this information estimated total energy expended per week during physical activity was calculated.

Additionally, men were put into groups based on the amount of activity that was completed. These groups can be found below:

Blocks walked	Flights climbed	Sports/Recreation (energy expenditure, kj/week)
Group 1: <5	Group 1: <10	Group 1: None
Group 2: 5 – 10	Group 2: 10 – 20	Group 2: 1 – 1,050
Group 3: 10 – 20	Group 3: 20 – 35	Group 3: 1,050 – 2,520
Group 4: >20	Group 4: >35	Group 4: 2,520 – 5,880

This initial 1977 questionnaire also inquired about height, weight and cigarette smoking. They were asked if they currently smoke, if so, how many cigarettes smoked daily. Smoking history details were also collected. In 1988 and again in 1993 health surveys were sent to surveying alumni. This survey inquired whether they have ever been diagnosed with cancer, if so, the site and year of initial diagnosis. Death certificates were used to identify prevalence of lung cancer in alumni who had passed away.

The main limitation of this methodology is the use of health questionnaires. The use of such questionnaires causes inevitable bias due to overestimation and underestimation. With cohorts of such a large size this is the only practical option, however, this will skew data. Another limitation is the length of the overall study. From the initial identification in 1916 to the publish date of 1999, this is a 83 year long study which is very resource and time inefficient. The last main limitation is the cohort used. This cohort is very specific and does not represent most of the world’s population as it completely neglects women and men that didn’t attend university.

What were the basic results?

• During the follow up from 1977 through until 1993, 245 of the 13,905 men developed lung cancer.
• Findings also showed higher levels of energy expenditure was associated with lower lung cancer incidence rates. Men who expended >12,600kj/week had a significantly lower risk of developing lung cancer compared to those expending <4,600kj/week
• Next development of lung cancer among smokers (>20 cigarettes/day) and non-smokers (or former smokers) was analysed. It was found that roughly 0.01% of non-smokers developed lung cancer while roughly 0.07% of heavy smokers developed lung cancer.
• In the research article they used total number of cases rather than percentages which did not distinguish the clear difference in prevalence. In the article they say the findings are ‘not significant’ although there is a 700% increase in prevalence. The use of percentages in this instance would have made it easier to identify this.
• Lastly the different forms of physical activities effect on the development of lung cancer was assessed. Larger amounts of all modes of physical activity assessed positively correlated with a lower risk of developing lung cancer.

What conclusions can we take from this research?

The main finding from this research is that physical activity of all modes seems to be inversely associated with lung cancer among men. In addition, heavy smoking seems to significantly increase the chances developing lung cancer.

The key strength of this study is its population size, a population size of 13,905 is very strong which limits the influence of bias.

The key limitation of this study is the questionnaires used to gather information due to the heavy influence of overestimation and underestimation bias. The research is also specific to males who have attended university, which leaves out many populations including women.

There are numerous studies that have explored the correlation between lung cancer and physical activity which have come to conflicting results. Some have come to the same conclusion that they are inversely associated (7, 9). While others conclude no association at all (10, 11).

Practical advice

Using the information presented in this research, participating in physical activity in some capacity will be beneficial in lowering the chances of developing lung cancer. The research has also shown that intensity or form of exercise is not the most important factor, it’s about total energy expenditure. Finding something that suits the individual and that is enjoyable will be crucial in maintaining motivation.

Many studies have stressed the strong association between smoking and lung cancer (12). Finding a way to cut this out will be extremely beneficial.

Research has shown that survivors and people currently living with lung cancer are more depressed and physically weaker. Seeking attention from a psychologist and health professional will be extremely beneficial for such populations.

For those currently living with lung cancer seeking treatment such as surgery, chemotherapy, radiation therapy or targeted therapy will be essential in monitoring and killing the cancer cells (6).

Further information/resources

For further information on lung cancer visit these pages below:

• https://www.cancer.org.au/cancer-information/types-of-cancer/lung-cancer
• https://www.cdc.gov/cancer/lung/basic_info/diagnosis_treatment.htm#:~:text=it%20has%20spread.-,People%20with%20non%2Dsmall%20cell%20lung%20cancer%20can%20be%20treated,doctors%20cut%20out%20cancer%20tissue