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Aug. 23 (UPI) -- It isn't the time that older adults spend sitting, but rather the type of sedentary activity that affects dementia risk, a new study says. Watching TV may increase the risk, but curling up on the couch with a laptop may reduce it. Researchers said their National Institutes of Health-funded study also debunks the idea that if people are more physically active during the day, they are able to counter the negative effects of time spent sitting.
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According to the study, by reducing time spent in "cognitively passive" sedentary behaviors, such as TV time, and increasing time spent in "cognitively active" sedentary behaviors, such as computer time, adults aged 60 and older may benefit brain health -- even if they are very physically active.
The findings by researchers at the University of Southern California and University of Arizona were published this week in Proceedings of the National Academy of Sciences.
David Raichlen, the study's lead author and professor of biological sciences and anthropology at USC, said the study shows what people do while they're sitting matters -- and shifting from passive to active sedentary behaviors may reduce dementia risk.
"As with any observational study, we can't determine causality," he told UPI in an email. "But we think this study forms a strong foundation for future interventions to determine the best ways to alter sedentary behavior to improve brain health and reduce dementia risk."
According to Raichlen, a large body of research has focused on the associations of physical activity with brain health, but much less work has examined whether sedentary behaviors or inactivity is linked with risk of dementia in older adults.
So the researchers set out to investigate whether sitting around is associated with dementia regardless of whether people engage in physical activity.
"We found that sedentary behaviors were associated with dementia risk, but surprisingly, what we do when we're sedentary impacts the direction of that risk," Raichlen said.
He added: "Physical activity, while linked with reduced dementia risk overall, did not greatly alter the associations between sedentary behavior and brain health."
According to the researchers, watching TV doesn't involve much muscle activity or energy use, and previous research has shown uninterrupted sitting for long periods of time is related to reduced blood flow in the brain, But greater intellectual stimulation that occurs during computer use may counteract the negative effects of sitting.
The study included self-reported data from the U.K. Biobank, a biomedical database of 500,000-plus participants across the United Kingdom. It explored the two types of sedentary behavior, leisure-time computer use and TV watching, based on the biobank's questionnaires.
None of the 145,000-plus biobank participants aged 60 and older had a diagnosis of dementia at the start of the study. They used questionnaires to self-report information about levels of sedentary behavior during the 2006 to 2010 baseline period.
After roughly 12 years of follow up, the researchers used hospital inpatient records to seek dementia diagnoses -- and they found 3,507 positive cases.
They then adjusted for demographics that could affect brain health, such as age, sex, race/ethnicity and job type, as well as lifestyle characteristics, including exercise, smoking and alcohol use, time spent sleeping and engaging in social contact.
According to Raichlen, the researchers focused on older adults because they were interested in the development of late-onset dementia, rather than neurodegenerative diseases that affect younger adults or middle-aged adults.
"However, we did include a sensitivity analysis of the full sample [aged 40 and older] and the results were the same," he said.
