Sitting and Risk for Cancer Death; Moving Even a Little Helps

Laird Harrison

June 23, 2020

Being sedentary was associated with a greatly increased risk for cancer death, but even very light exercise, such as a short daily walk, can help, say researchers reporting data from a cohort of people who wore accelerometers.

The study was published on June 18 in JAMA Oncology.

The finding offers hope for people who are unable to engage in more vigorous activities, such as running or cycling, said lead author Susan Gilchrist, MD, an associate professor of clinical cancer prevention and cardiology at the University of Texas MD Anderson Cancer Center in Houston.

"It gives people some realistic goals for what they can do for themselves," Gilchrist told Medscape Medical News.

Some previous studies have found an association between sedentary activity and cancer mortality, but others have shown no association. All have relied on participants' self-reports as to their own activity, but most people underestimate how much time they spend sitting, she commented. Also, researchers have had trouble teasing out the benefits of exercise from the harm of motionlessness, Gilchrist said.

To overcome these limitations, her team analyzed data from a cohort of 8002 people who were part of the Reasons for Geographic and Racial Differences in Stroke (REGARDS) and who wore accelerometers. REGARDS is a national study of stroke risk factors. It involved 30,239 black and white US adults older than 44 years who were recruited between 2003 and 2007.

One group of participants wore accelerometers on their hips during waking hours for 7 consecutive days. The mean age of these participants was 69.8 years, and 45.8% were men. None were being treated for cancer at baseline.

The REGARDS researchers collected the accelerometer data from 2009 to 2012. The mean follow-up period was 5.3 years. During that time, 268 participants died of cancer.

The team reports that those participants who died of cancer had spent more minutes per day being sedentary, were sedentary for longer periods at a stretch, and performed less light-intensity physical activity (LIPA) and moderate- to vigorous-intensity physical activity (MVPA).

LIPA generally includes activities such as light housework, shopping, cooking, and easy gardening; MVPA encompasses a wide range of more strenuous activity, including brisk walking, running, dancing, and digging ditches.

The researchers found that participants who spent the most time being sedentary were 82% more likely to die from cancer (hazard ratio [HR], 1.82; 95% confidence interval [CI], 1.27 – 2.60).

The researchers adjusted for age, race, sex, region of residence, educational level, season the accelerometer was worn, current smoking, alcohol use, body mass index, diabetes, hypertension, dyslipidemia, history of coronary heart disease, history of stroke, and MVPA. Even after these adjustments, they found that the most sedentary people were 52% more likely to die of cancer (HR, 1.52; 95% CI, 1.02 – 2.27).

People who were sedentary for the longest bouts were also 61% more likely to die of cancer (HR, 1.61; 95% CI, 1.16 – 2.24), but after the researchers adjusted for the other factors, the increased risk was no longer statistically significant (HR, 1.36; 95% CI, 0.96 – 1.93).

For every 1 hour that participants spent being sedentary, their risk of dying from cancer increased by 16% (HR, 1.16; 95% CI, 1.03 – 1.31).

On the other hand, substituting 30 minutes of sedentary time with 30 minutes of MVPA a day lowered the risk for cancer death by 31% (HR, 0.69; 95% CI, 0.48 – 0.97). Thirty minutes of LIPA per day reduced the risk by 8% (HR, 0.92; 95% CI, 0.86 – 0.97).

"The thing that surprised me was that light activity was significant," Gilchrist said. "I thought that you would have to replace the sitting activity with moderate to vigorous activity."

This kind of granular association would have been hard to uncover with self-reported data, she said. It is good news for people with sedentary lifestyles and for the physicians trying to help them, she added.

Gilchrist works with patients who find exercise difficult in the best of times and have given up since the COVID-19 pandemic has made group activities and gyms more dangerous. "Let's move around the house for 10 minutes," she tells them. "Let's go to the mailbox and back."

She acknowledged several limitations to the study. Among the most important is that the patients wore the accelerometers on their hips, so the devices couldn't detect differences between sitting and standing and so would not capture activities such as washing dishes.

Although only a clinical trial could prove cause and effect, this study made an important contribution because it provided objective measurements and because it spanned 13 years, said Nigel Brockton, PhD, vice president of research at the American Institute for Cancer Research in Washington, DC.

"This helps with the messaging," he said. "So many people are wearing wearable devices to quantify their own activity."

It is significant that the association of physical activity and cancer mortality in this study was independent of body mass index, Brockton said. Although it's not yet clear how exercise might reduce cancer, the evidence so far points to effects on both metabolism and inflammation, he said.

In the next phase of her research, Gilchrist hopes to zero in on the effects of physical activity on specific types of cancer. That might help answer some of these biochemical questions.

Gilchrist has served as a consultant for Outcomes4Me. Brockton has disclosed no relevant financial relationships.

JAMA Oncol. Published online June 18, 2020. Abstract

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