How long a person spends sitting should now be part of CVD risk assessment - as well as how much they exercise.
Too much sitting – independent of exercise levels – is a distinct risk factor that clinicians can use to guide cardiovascular disease prevention and rehabilitation, experts say.
Public health guidelines needed to explicitly address sedentary behaviour, given its independent association with cardiovascular disease, said researchers in Nature Reviews Cardiology after their review found that simple interventions could reduce sitting times and increase physical activity.
Evidence is building that prolonged sitting could blunt the well-established benefits of exercise, the authors said. And alongside this sitting-induced “exercise resistance”, sitting might also increase cardiovascular disease risk by acting through a variety of mechanisms including vascular function, blood pressure, blood glucose and cerebral blood flow.
The Health Department currently had specific physical activity guidelines for the general population, but recommendations on sitting extended only to limiting recreational screen time to less than two hours per day for children and to “reduce” sedentary time for adults.
“Traditionally we have focused on moving more for all promotional efforts in the physical activity area,” said Professor David Dunstan, lead author and head of physical activity research at the Baker Institute in Melbourne.
“But increasingly we’re seeing from observational and experimental research that we need to consider both ‘sitting less’ and ‘moving more’ because the interplay appears to be of great importance for many medical conditions … the overwhelming evidence is that if you’re physically inactive, and you’re sitting for high amounts of time, you are most at risk.”
Professor Dunstan said two simple questions could help clinicians assess patients’ risk: “roughly how many hours do you spend sitting?”, and “how many minutes do you spend on physical activity in a usual day?”
For highly sedentary workers, Professor Dunstan encouraged standing up and moving for six minutes every half-hour to an hour, in addition to a brisk 30-minute walk before or after work.
“If someone is retired, the TV screen can be quite pervasive in the home, so try using advertisement breaks to move around, break up those prolonged uninterrupted periods of sitting … think about little chores you could do while watching TV, such as folding the washing or doing the dishes,” he said.
A starting goal might be reducing total sitting time by 30 minutes per day, which might initially involve standing or light-intensity activities to build up patients’ physical conditioning.
The team’s review of more than 30 trials of interventions to reduce sitting time in adults found environmental change such as a sit-stand desk was most effective, reducing sitting by around 40 minutes a day.
This was followed by interventions combining environmental and educational components, such as smartphone apps and educational programs reminding people to move at set intervals (36-minute reductions).
Given the authors also said device-based estimates from large cohorts now suggested adults sit more than previously suggested by self-reports (between almost eight and 11.5 hours a day rather than between five and eight), the reductions might not seem significant.
“But if it can translate into 40 minutes of more moving, it’s likely to have quite powerful benefits for people living with a condition like type 2 diabetes,” Professor Dunstan said.
“It’s important to note a lot of the studies on reduction of sitting time have been in generally healthy populations – we simply don’t have the evidence at present for those clinical conditions that GPs are going to be seeing.”
