Physical Activity & Prostate Cancer

Prostate Cancer

Prostate cancer is the most common cancer among Canadian men (excluding nonmelanoma skin cancer), with 1 in 8 Canadian men expected to develop the disease in his lifetime, and 1 in 28 expected to die from it.^[1] In Canada, the five-year survival rate for prostate cancer is 96%; however, despite this promising statistic, every day an average of 65 Canadian men will be diagnosed with prostate cancer, and 11 will die from it.^[1] According to the Canadian Cancer Society, prostate cancer incidence rates have increased since 1980, which may, in part, be due to population aging, lowering of the prostate-specific antigen (PSA, a measure of prostate health) threshold for biopsy, more extensive screening, and improved sensitivity of prostate biopsy.^[2] Increases in prevalence is seen in all age groups younger than 70 years, while the highest average annual rate increases are seen in 40–49-year-olds. Interestingly, an inverse relationship between prostate cancer prevalence and ages greater than 70 years appears to exist, as demonstrated by attenuated increases in rates among Canadian men aged 70–79 and significant declining trends among those greater than 80 years of age.^[2]

The Canadian Cancer Society has identified several established and potential risk factors for the development of prostate cancer:^[3]

Source: “Risk Factors for Prostate Cancer.” Canadian Cancer Encyclopedia from the Canadian Cancer Society. Canadian Cancer Society.
 

Relationship Between Physical Activity and Prostate Cancer

According to the Canadian Cancer Society, lack of physical activity is not identified as either a possible or known risk factor for the development of prostate cancer.^[3] However, it has been suggested that an association between increased physical activity and decreased prostate cancer risk probably exists.^[7] Although inconsistent findings have been demonstrated, several reviews have suggested risk reductions averaging 10–30%.^{[7, 8, 9]} Following the old adage, “an ounce of prevention is worth a pound of cure”, this article will further investigate and analyze existing research on the role of physical activity in the primary prevention of prostate cancer.

Physical activity is defined as “any bodily movement produced by skeletal muscles that results in a quantifiable expenditure of energy” and is categorized into occupational and leisure-time physical activities.^[4] This definition has been expanded to include four primary components: intensity (amount of energy expended), duration (length of activity episode), frequency (episodes performed per unit time), and time period in which the physical activity is engaged (adolescence or adulthood).^{[4, 5]} Furthermore, physical activity intensity is commonly quantified using metabolic equivalent (MET) values. MET refers to the ratio of the associated metabolic rate for a specific activity to the resting metabolic rate. To provide context and perspective, 1 MET is 3.5 mL O2/kg/min and represents the average seated energy expenditure of an adult; 3 METs reflects low intensity activities (i.e. walking slowly) and 6 METs or more reflects vigorous activities (i.e. running, basketball, hiking).^[6]

Physical activity has been postulated to reduce the risk of prostate cancer due to the following potential reasons: lower levels of circulating testosterone, insulin, glucose, and insulin-like growth factors (hormones known to play a role in prostate cancer); decreased obesity; and possible exercise-induced increases in antitumour activity and antioxidant defense mechanisms.^{[8, 9, 10]} However, the actual causal association between physical activity and prostate cancer is still unclear.^[8]

So What Does the Evidence Say?

A large prospective cohort study of 72,174 men aged 50–74 found that recreational physical activity of ≥ 35 MET-hours per week (three and a half hours of vigorous activity per week) was associated with a 31% lower risk of aggressive prostate cancer at time of diagnosis, but did not impact overall prostate cancer risk.^[10] The findings of this study were consistent with previous research which also failed to demonstrate a significant positive impact of physical activity on prostate cancer risk. However, this study elucidated a potential impact of physical activity on the severity of prostate cancer and encourages further research in this area.

Another prospective cohort study of 47,620 American male health professionals, aged 40–75, assessed the association between physical activity and prostate cancer incidence and progression.^[11] Physical activity was assessed through participant recall of average time per week spent doing activities such as walking, jogging, bicycling, and so on, during the previous year. This study also considered number of flights of stairs climbed daily and the usual walking pace, as well as heavy outdoor work and weight training. The authors demonstrated that men ≥ 65 years old who engaged in 30 METhours per week (three hours of vigorous activity per week) versus zero MET-hours per week experienced a reduced risk of being diagnosed with advanced or fatal prostate cancer by almost 70%. This study also sheds light on the relationship between physical activity and the severity of prostate cancer diagnosis and progression.

Furthermore, a population-based case-control study matched 988 patients with diagnosed prostate cancer to 1036 population controls.^[12] The Lifetime Total Physical Activity Questionnaire was used to measure occupational, household, and recreational activity levels from childhood right up to diagnosis. Additionally, participants reported personal health history, prostate cancer screening history, prostate conditions, history of surgery, family history of cancer, lifetime physical activity patterns, dietary intake during the reference year, lifetime alcohol consumption history, smoking habits, demographic characteristics, and usual adult height and weight at each decade of age from 20 to 60 years. Ultimately, this study demonstrated no association between total lifetime physical activity and prostate cancer risk. However, a decreased risk of 30% was seen when physical activity was conducted during the first 18 years of life. Decreased risk was also seen when vigorous activity (> 6 METs, such as backpacking/hiking, weightlifting, swimming, or running) was performed, compared to low-intensity physical activity (< 3 METs, such as walking slowly).

Current evidence indicates a possible link between physical activity and reduced prostate cancer risk, although there is no conclusive proof. This may be due to the studies failing to include a population with sufficient numbers of participants who engage in high levels of physical activity, a lack of standardization in methods, incomplete inclusion of components of physical activity (type, frequency, duration, intensity, time of life), patient misclassification of recalled information, absence of relevant subgroups (obese, nonobese, athletic, ethnicity, caloric intake, etc.), lack of clinical trials, and confounding factors (association of physical activity with other healthy lifestyle and dietary habits). These limitations complicate the interpretation and comparison process associated with these studies.

In the realm of naturopathic medicine, there is seldom a treatment plan that only incorporates a single intervention. So when the topic of prevention of prostate cancer is explored, physical activity represents a single slice of a larger pie, which also includes dietary habits, mental and emotional well-being, environmental exposures, infectious agents, and so on. There has been encouraging data on the impact of healthy lifestyle changes on prostate cancer progression, and hopefully future research will explore role of physical activity in conjunction with various other healthy lifestyle habits in reducing the risk of developing prostate cancer.^[13] This would better reflect the comprehensive and synergistic nature of naturopathic medical interventions as applied in clinical settings.

Additional Considerations for Prostate Health

One of the great values naturopathic doctors offer is the ability to draw from various treatment modalities to help patients achieve their goals and optimize their well-being. As a result, a brief exploration into additional considerations for prostate health will be reviewed.

From a dietary standpoint, plant-based diets are often emphasized as a foundation for healthy living. When incorporating vegetables and fruits into a diet to support cancer prevention, it is recommended that at least five servings be consumed.^[14] In addition to including plants in the diet, effort should be made to reduce the intake of sugar. High sugar intake (in the form of sugar-sweetened beverages), compared to zero intake, contributed to greater than a 30% increased risk of developing the disease.^[15] Further, fibre intake is often overlooked for its ability to support healthy prostate health, which is accomplished by supporting normal hormone regulation. It has been found that daily dietary fibre intake greater than 20 g, compared to less than 13 g, corresponded to approximately 50% decreased risk of prostate cancer.^[16] Lastly, adding three to five cups of green tea per day to one’s dietary regimen can have positive impacts on overall cancer prevention.^[17]

 Conclusion

As it stands, the three risk factors for prostate cancer are nonmodifiable: family history, age, and ethnicity. However, one’s health is not defined solely by these factors, and effort must be made to encourage lifestyle choices that are supportive of the greatest potential for health, regardless of nonmodifiable factors. The American Cancer Society, the US Department of Health and Human Services, the International Union Against Cancer, the World Cancer Research Fund, the American Institute for Cancer Research, the Harvard Center for Cancer Prevention, the Canadian Cancer Society, and Health Canada generally recommend at least 30 minutes of moderate to vigorous physical activity five days per week for general cancer prevention.^[8] Physical activity in this context includes anything at an intensity that brings the participant to a sweat, including brisk walking, heavy housework, or recreational sports. Based on this analysis of research pertaining to prostate cancer specifically, no definitive conclusion can be made with respect to physical activity on its own for primary prevention. Future research, taking the aforementioned limitations into consideration, and encompassing a strategic and synergistic combination of dietary and lifestyle changes, is warranted. However, despite inconsistent findings, physical activity has been associated with prostate cancer risk reductions averaging 10–30% and positive impacts on prostate cancer severity and progression.^[7–12] Moreover, physical activity has been shown to decrease insulin levels, blood glucose levels, plasma lipid concentration, body mass index, and is associated with overall healthier lifestyle habits.^[6] Combined with the fact that there are no adverse effects (except with strenuous physical activity) and this intervention can be free of cost, three hours per week of vigorous physical activity should be advised to men of all age groups, particularly to those ≤ 18 and ≥ 65, as an adjunctive tool for the mitigation of prostate cancer risk.