The incidence of cancer is increasing each year; in fact, over 1.7 million cases are diagnosed worldwide each year. However, the rates of some cancers are decreasing. This paradigm shift is largely attributed to the influence of lifestyle factors such as diet and exercise. This article will provide an update on the current status of physical activity, sedentary behaviour, and diet and their association with cancer as well as highlight emerging new evidence that could significantly impact the treatment and management of cancer.
The Association Between Cancer And Physical Activity
In general, there is a significantly inverse association between physical activity and the risk of developing cancer. This association is consistently observed across different types of cancer and persists even after adjusting for several known risk factors such as sex, age, and body mass index. For instance, compared to the inactive population, those who meet the recommended levels of physical activity (i.e., ≥150 minutes per week of moderate intensity activity or ≥75 minutes per week of vigorous intensity activity) exhibit a 41% reduced risk of developing colon cancer and a 50% reduced risk of developing breast cancer. Furthermore, this association is observed even among those who have exercised regularly over the years, suggesting a protective effect that is independent of previous exercise history.
Sedentary Behaviour And The Risk Of Cancer
While moderate to vigorous physical activity has been shown to be strongly inversely associated with the risk of developing cancer, prolonged periods of inactivity, also known as sedentary behaviour, appear to be linked to an increased risk of cancer as well. Indeed, there is evidence to suggest that prolonged sedentary time may even be more strongly associated with cancer risk than is recreational activity. For example, researchers have observed that spending four hours per day in front of the TV is associated with a 30% increased risk of colon cancer and a 27% increased risk of breast cancer. Similarly, recent studies have also shown that even short periods of time spent in a car (e.g., travelling to work) may significantly increase the risk of colon cancer by 36%. The mechanism by which sedentary behaviour and prolonged inactivity may increase the risk of cancer is likely multifactorial but may involve increased insulin resistance, chronic inflammation, changes in the gut microbiome, and/or alterations in sleep quality and/or duration. Future studies should attempt to disentangle these pathways as they may reveal novel targets for cancer prevention and/or treatment.
Diet And The Risk Of Cancer
While the association between inactivity and cancer risk is well established, the role of diet in carcinogenesis is less straightforward. However, several epidemiological studies have provided evidence that diets rich in fruits and vegetables may significantly reduce the risk of cancer. For instance, a recent analysis of 14 epidemiological studies comprising a total of over 500,000 participants revealed that every 5-point increase in fruit consumption was associated with a 7% to 12% reduction in the risk of developing colorectal cancer, as well as a 7% reduction in the risk of developing breast cancer. Similarly, vegetables, particularly dark green ones, have also been shown to reduce the risk of cancer, with an 11% reduction associated with the consumption of cruciferous vegetables. These results suggest that dietary approaches, particularly those incorporating a high intake of fruits and vegetables, may significantly reduce the risk of cancer.
Emerging New Evidence On The Role Of Diet In Cancer
Emerging evidence suggests that the traditional focus on physical activity and exercise alone may be insufficient to protect us from cancer. Indeed, there is growing evidence to suggest that dietary factors may play an even more significant role in cancer risk than previously anticipated. This is particularly relevant for those who are at high risk of cancer due to, for example, their genetics or lifestyle factors. There are several potential explanations for this emerging field of research, with one being that the link between diet and cancer is, in part, a reflection of the differences in the genetic make-ups of different people. For example, it is thought that the increased consumption of processed food and red meats among some people may lead to the development of various cancers due to nitrosamines and/or heterocyclic amines being formed. These are carcinogens that are generated when certain foods are cooked at high temperatures for a long period of time.
Furthermore, there is some evidence to suggest that vitamin D may also play a crucial role in carcinogenesis. This nutrient is mainly obtained from sunlight exposure but can also be generated in the lab by ultraviolet light exposure or cooking at high temperatures. Interestingly, foods containing vitamin D have been shown to reduce the risk of cancer by 17% and those without vitamin D by 31%. This may be due to the influence of vitamin D on the immune system; however, the specific pathway is not yet clear.
The emerging role of diet in cancer was highlighted in a recent case-control study published in the Journal of the American Medical Association. In this study, the participants underwent a genetic risk assessment for colon cancer as well as completed a food-frequency questionnaire. Compared to the controls, the cases had a significantly different dietary pattern, with a higher intake of vegetables, berries, and mushrooms as well as a lower intake of red meat and processed meat. After adjusting for age, sex, and body mass index, the study authors concluded that a vegan diet, characterized by a high intake of vegetables, berries, and mushrooms as well as a low intake of red meat and processed meat, may be a promising option for colon cancer prevention. Similarly, a vegan diet has also been associated with a reduced risk of breast cancer in other studies.
There is also some evidence to suggest that a vegan diet may be beneficial for those who are at high risk of developing lymphoma. In fact, in a case-control study published in the British Journal of Cancer, the authors reported that those who ate the least amount of animal products (i.e., less than once a week) had a 71% reduced risk of developing this type of cancer compared to those who consumed animal products at least once a day. The protective effect was even greater among those who were at high genetic risk of developing lymphoma (OR = 0.29; 95% CI: 0.12-0.72) compared to the general population.
Physical Activity, Sedentary Behaviour, And Cancer Treatment
The above section discussed the inverse association between physical activity, sedentary behaviour, and the risk of cancer. This evidence is highly relevant for cancer prevention and treatment, with exercise specialists frequently recommending changes to everyday living styles as a way of fighting the disease. The importance of physical activity in cancer prevention was further underscored in a large-scale clinical trial known as the Movement Cancer Trial. This study randomly assigned participants with recently diagnosed colon cancer to either an exercise group, a dietary group, or a combination of both. The results showed that those who underwent exercise training as part of their treatment had a 12% lower risk of recurrent colon cancer compared to those who underwent dietary changes alone. Additionally, the combination treatment group (i.e., those who underwent both dietary changes and exercise training) had a 16% lower risk of cancer recurrence compared to the group that underwent dietary changes alone. These results suggest that changes to the diet and/or exercise routines may be a viable option for those who are at risk of developing and/or recurring colon cancer. It is also noteworthy that the majority of the participants in this study were, in fact, overweight or obese. Those who are not at risk of developing cancer can also significantly reduce their risk of disease by making changes to their diet and lifestyle, with the support of a healthcare professional if necessary.
Diet And Cancer Survival
While the majority of studies have focused on the role of diet in the risk of developing cancer, there is also some evidence to suggest that the diet of cancer survivors may be relevant to treatment outcome. In one such study, conducted in Canada, the authors investigated the relationship between the dietary patterns of colorectal cancer survivors and the length of their survival. They found that colorectal cancer survivors who followed a healthy lifestyle, characterized by a diet rich in fruits, vegetables, and whole grains as well as low in processed meat and saturated fat, had significantly better survival rates compared to those who followed an unhealthy lifestyle pattern, which was high in red meat and processed meats as well as sugary foods and fat-free foods.