Regular physical activity prior to a cancer diagnosis may be linked to a lower risk of disease progression and mortality, according to a recent study published by Mabena et al in British Journal of Sports Medicine. The findings revealed that even relatively low levels of physical activity may be advantageous.
Background
Although there is compelling evidence that physical activity plays a key role in lowering the risk of cancer-related mortality, the evidence isn’t as conclusive for its role in disease progression.
Study Methods and Results
In the study, investigators analyzed anonymized data from the Discovery Health Medical Scheme (DHMS)—the largest open medical plan in South Africa, covering approximately 2.8 million beneficiaries—linked to the Vitality health promotion program. All Vitality health promotion program participants were rewarded for adopting healthy lifestyle behaviors, earning points for physical activity recorded by activity trackers, logged gym attendance, or registered participation in organized fitness activities.
Activity type, frequency, duration, and intensity were recorded and translated into weekly minutes of exercise.
In all, 28,248 Vitality health promotion program members with stage I cancers and comprehensive physical activity data for the year preceding diagnosis were included in the study, which spanned the period from 2007 to 2022. Breast and prostate cancers were the most common cancer types, comprising 44% of the study total. The length of time between initial diagnosis and disease progression, mortality, or exit from the study ranged from 1 month to nearly 13 years.
The investigators noted that cancer didn’t progress in 65.5% of the total sample, but cancer did progress in 34.5% of the sample. While 81% of the participants survived, 19% died prior to the completion of the study. The average time to mortality was 20 months and the average time to progression was 7 months.
Levels of physical activity in the year prior to diagnosis were categorized as none recorded (62%, n = 17,457); low, equal to 60 or fewer weekly minutes (13%, n = 3,722); and moderate to high, equal to 60 or more weekly minutes of moderate intensity physical activity (25%, n = 7,069).
After accounting for potentially influential factors—including age at diagnosis, sex, economic and social position, and coexisting conditions—rates of cancer progression and all-cause mortality were lower among those who were physically active in the year preceding their diagnosis.
The risk of disease progression was 16% lower among those who had engaged in low levels of physical activity in the preceding year compared with those who hadn’t recorded any physical activity, whereas the risk among those who had engaged in moderate to high levels were 27% lower.
Similarly, the risk of all-cause mortality was 33% lower among those who had engaged in low levels of physical activity compared with those who hadn’t recorded any, and 47% lower among those who had managed moderate to high levels.
Two years postdiagnosis, the likelihood of no disease progression among those with no recorded physical activity in the year before diagnosis was 74% compared with 78% and 80%, respectively, among those achieving low and moderate to high levels of physical activity.
While the likelihood of disease progression increased as time went on, it was still lower among the participants who had recorded some level of physical activity in the year preceding their diagnosis.
After 3 years, the likelihood of no disease progression was 71%, 75%, and 78%, respectively, among those who partook in no, low, and moderate to high levels of physical activity. After 5 years, the likelihood was 66%, 70%, and 73%, respectively.
Similar patterns were evident for all-cause mortality. Two years following cancer diagnosis, the probability of survival among those with no documented physical activity in the year preceding diagnosis was 91% compared with 94% and 95%, respectively, among those who had recorded low and moderate to high levels.
The equivalent probabilities of survival 3 years postdiagnosis were 88%, 92%, and 94%, respectively; and 84%, 90%, and 91%, respectively, after 5 years.
Conclusions
Because the study was observational in nature, the investigators were unable to establish cause and effect. They acknowledged that they weren’t able to account for other potentially influential factors, such as smoking and alcohol consumption, while the data on weight (body mass index) were incomplete.
However, there were several plausible biological explanations for the findings. Chief among them was the way in which physical activity strengthened immunity by increasing numbers of natural killer cells, lymphocytes, neutrophils, and eosinophils.
Physical activity may also lower the cancer progression risk of hormone-sensitive cancers such as breast and prostate cancers by regulating estrogen and testosterone levels.
“Physical activity may be considered to confer substantial benefits in terms of progression and overall mortality to those diagnosed with cancer,” the study authors emphasized. “In a world where cancer continues to be a significant public health burden, the promotion of physical activity can yield important benefits regarding the progression of cancer as well as its prevention and management,” they concluded.
Disclosure: For full disclosures of the study authors, visit bjsm.bmj.com.
