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Jody Holmes, 46, was diagnosed with breast cancer at 42 and participated in the exercise intervention in the UBC study.John Lehmann/The Globe and Mail

Up until her diagnosis of breast cancer, at age 42, Jody Holmes had a memory "like a steel trap," she said. Holmes, a conservation biologist and director at the Rainforest Solutions Project, was one of the architects of a historic 2009 agreement with the B.C. government, forestry industry and First Nations to conserve Canada's Great Bear Rainforest.

But after a double mastectomy and two years of radiation and chemotherapy, she began to suffer from what cancer survivors call "chemo brain." Holmes, now 46, said she had trouble finding the right words and remembering people's names, and felt "a relatively high level of fuzziness about how to get things done."

Then, last year, Holmes agreed to join 18 other women in a small study looking at whether exercise could improve post-chemotherapy cognitive impairment.

During the 24-week study period, Holmes got 150 minutes of vigorous aerobic exercise each week, including two 45-minute sessions with a trainer at a treadmill or elliptical machine and two half-hour sessions of cycling or swimming on her own.

Partway through the study, she said, her thinking became clearer and she began to have an easier time planning meals, after-school activities for her eight-year-old daughter and chores for the week.

"I felt I was a little more in control of my life," Holmes said, adding that her co-workers began to say things like, "Wow, you're back."

Chemo brain – also known as "chemo fog" – is a common yet nebulous side effect of cancer treatments. Months or even years after radiation and chemotherapy, cancer survivors may suffer from mental confusion and problems with short-term memory that interfere with their ability to follow the gist of a conversation, put names to faces and do everyday tasks, such as folding laundry, in a normal period of time.

Some studies suggest that up to 50 per cent of breast-cancer patients experience symptoms of chemo brain. According to the Mayo Clinic, the cognitive impairments may be caused by chemotherapy as well as other cancer treatments, including radiation, hormone treatment, stem-cell transplant and surgery.

Researchers have yet to come up with a clear definition and reliable diagnostic test for chemo brain, said Dr. Kristin Campbell, lead researcher of the exercise study and an assistant professor of physical therapy at the University of British Columbia.

Nevertheless, it's a "real issue," Campbell said.

She added that doctors have little guidance on how to help cancer survivors suffering from cognitive impairment, even though chemo brain can be bad enough to prevent patients from returning to their normal jobs.

Campbell and colleagues recruited women treated for early-stage breast cancer in advance of the pilot study, presented in early June at the annual meeting of the American Society of Clinical Oncology in Chicago. All participants, aged 40 to 65, were sedentary in the previous six months and had symptoms of chemo brain, but no risk factors for cognitive impairment other than cancer treatments.

At the beginning and end of the 24-week study period, the women completed standard questionnaires to assess their perceived cognitive impairments, had neuropsychological tests to measure how well they remembered things in categories such as animals or weapons, and their brain activity measured with functional MRI.

At the end of the study, women in both the control and exercise groups showed little difference in their neuropsychological test results and self-reported cognitive functioning. However, the brain-imaging tests showed significantly increased activity in the exercise group in brain regions known to support task performance, attention and decision-making, Campbell said.

"The main thing we're excited about are the neuro-imaging findings," she said.

Previous studies have shown that exercise may support brain health by improving blood flow to the brain and boosting neurotransmitters that support brain function. The benefits of exercise may not be unique to chemo-brain sufferers, Campbell pointed out, "but exercise may help these women with some of the symptoms they are experiencing," she said.

Campbell speculated that a larger follow-up study might show correlation between the brain-imaging results and neuropsychological tests. But based on the study's preliminary results, "it's worth pursuing more research," she said.

In the meantime, Holmes has no way of knowing whether her chemo fog would have lifted with time alone. Nevertheless, Holmes said she does her best to maintain her workout routine, since regular exercise seems to increase her energy levels and improve her moods.

Now that it's summer, Holmes is swimming outdoors for 45 minutes, five days a week, and describes her saltwater swims at Vancouver's Kitsilano Pool as "my idea of heaven."