Physical activity appears to clear away brain fog and significantly improve cognitive function in breast cancer survivors experiencing poor working memory and executive function following chemotherapy, according to researchers.
In a national study of 299 women with a mean duration of 8 years since chemotherapy for breast cancer, objective measures showed that moderate-to-vigorous physical activity (MVPA) was directly associated with significantly fewer cancer-related symptoms, such as fatigue (P < .001), say Diane K. Ehlers, from the Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, and colleagues.
Less fatigue was associated with faster times on executive function tasks (P = .005) and greater accuracy on working memory tasks (P = .03), they write in an online report published July 4 in Breast Cancer Research and Treatment.
A direct effect of MVPA on executive function was observed (P = .03), but there was no evidence of a direct path from MVPA to working memory (P = .76), the reserachers comment. Indirect paths paths from MVPA to cognitive performance, through fatigue, were also significant, showing improvements to executive function and memory (P = .02 and P < .05, respectively).
"The data suggest that being more physically active could reduce two of the more commonly reported symptoms in breast cancer survivors: fatigue and cognitive impairment," said study leader, Edward McAuley, PhD, in a statement. "Most people think, 'If I exercise, I'll become tired.' In our study, exercise actually was associated with reduced fatigue, which in turn was associated with better cognitive function."
These results are consistent with the literature on aging and cognition, support previous studies in cancer survivors, and extend earlier research suggesting that the effects of MVPA on cancer-related cognitive impairment may be partially explained by the influence of exercise on such symptoms as fatigue, the resereachers comment. Patients with cancer often report significant fatigue, as well as problems with memory, shortened attention span, and decreased ability to multitask — all of which closely resemble the signs of cognitive decline seen with aging, they point out.
The direct effect of MVPA on executive function suggests that brain structure and function may also contribute to the impact of exercise on cognitive function in breast cancer survivors. "Most of the available literature on the effects of exercise on brain health in cancer patients and survivors has focused on the hippocampus and memory functions," the study authors write. "Our findings support this research and suggest that memory may be a strong candidate for modifiable lifestyle intervention among cancer survivors." More research into the influence of exercise on health and function on the prefrontal cortex is needed, they add.
In an interview, Dr Ehlers said that the current study makes one of the strongest cases to date for cancer-related cognitive impairment being a neurobiological problem. She noted the study's large national sample and use of objective measures of both physical activity and cognitive function (using multiple indicators of cognitive function) to demonstrate positive relationships among MVPA, executive function, and working memory.
"From our perspective, looking at cognitive functioning, we're really excited to observe that the impact of cancer treatment on cognitive function is much the same as age-related cognitive impairment and uses similar neural pathways. More and more neurobiological studies are documenting this at a brain health level," she said, adding: "Now we're thinking that this is a real thing."
The benefits of physical activity on health and quality of life are well documented, with evidence showing that exercise can reduce risk for cancer recurrence; decrease fatigue, depression, and anxiety; and improve self-esteem and quality of life. Despite this, surveillance data indicate that breast cancer survivors may have as little as 3.7 minutes of moderate to vigorous physical activity each day, the study authors point out. "Identification of evidence-based treatments is critically needed," they say, pointing to the fact that improved breast cancer survival is creating a fast-growing population "at the intersection of cancer and aging."
For the study, breast cancer survivors completed a battery of questionnaires and neuropsychological tests measuring fatigue and cognitive function using a special iPad application created just for the study. Cognitive function was determined based on performance measures across seven cognitive tasks testing executive function and working memory. Mean age of the participants was 58 years, and about two thirds reported at least one chronic condition. Each participant wore an accelerometer for 7 consecutive days to measure their average daily exercise activity.
"We found that higher levels of daily moderate-to-vigorous physical activity were associated with better performance on the cognitive tasks measuring attention, memory and multitasking," Ehlers said in a statement. "What was notable was that physical activity's effect on cognitive performance was mediated by fatigue. This provides evidence that physical activity interventions targeting fatigue in cancer patients and survivors might provide promising models for improving cognitive function as well."
The standard of care for cancer survivors needs to change, Dr Ehlers told Medscape Medical News. Although integrated models of care — " à la cardiac rehab" — might be ideal, "We're not there yet," she acknowledged. Integrative care is expensive, and doctors "simply don't have the time or the training to deliver a behavioral prescription," she pointed out.
More evidence for the benefits of MVPA from the current study will be presented at the upcoming International Psycho-Oncology Society (IPOS) Congress in Berlin. Measurements of anxiety and depression show that women who were active before and after diagnosis had the highest quality-of-life (QoL) scores and the lowest levels of fatigue, depression and anxiety, said Dr Ehlers. They also reveal that women who were inactive prior to diagnosis but who got active after treatment had almost the same high QoL scores, and low measures of anxiety and depression.
Paradoxically, the highest levels of fatigue, anxiety, and depression and the lowest QoL scores were reported by women who were active before diagnosis but who became inactive afterward. Similar scores were seen in women who never exercised.
"The message is to get active, it's never too late," Dr Ehlers said, noting that even 10-minute bouts of brisk walking can have benefits. "Now we're trying to get people to stay active throughout [cancer] treatment, looking at the best kinds of exercise, and how much."
The next study, for which an iPhone app has been developed, will focus on diverse populations of breast cancer survivors, including those who have just completed cancer treatment.
This study is supported by the American Cancer Society. The authors have disclosed no relevant financial relationships.