How much sitting is bad for the heart?
Anyone else sitting around more? You aren't alone. Several studies have shown decreased levels of physical activity and increased sedentary time since the start of the pandemic. By now you probably know that exercise is good for the heart, but how does sedentary behavior affect your heart heart? How much sitting it too much? Here’s what the science says about sitting around and what I think you should do about it.
Physical inactivity is a risk factor for heart disease
Physical inactivity accounts for 9% of premature death worldwide and is independently responsible for many diseases, including 6% of heart disease. In fact, the relative risk of cardiovascular disease related to physical inactivity is similar in magnitude to cigarette smoking, high blood pressure, and cholesterol. So, moving our bodies is clearly important.
Physical inactivity is typically defined as not meeting the exercise goals as defined by national guidelines. As recommended by the American College of Cardiology/American Heart Association, this is currently 150 minutes of moderate intensity (or 75 minutes of vigorous activity) a week.
But what about what we do with the rest of our time? Despite the focus on moderate- and vigorous-intensity physical activity in the guidelines, this type of exercise activity accounts for a very small proportion of our time (0.2 hours of our day for the average American) as compared with other forms of activity. Does what we do on our “off time” affect the heart?
Sedentary lifestyle
Besides exercise, the other activity states that make up a 24-hour period for the average person include sleep, light-intensity physical activity, and sedentary behavior.
Sedentary behavior is defined as time spent in activities involving low levels of energy expenditure (such as sitting, watching television, and driving). Sedentary lifestyle (ie prolonged sitting time) has been identified as an independent risk factor for the development of premature heart disease. This is important because the average American spends almost 8 hours a day in sedentary activities.
What is non-exercise activity thermogenesis?
Non-exercise activity thermogenesis (or NEAT) is anything that isn’t sleeping, sitting, or exercise (aka “light-intensity physical activity”). It’s our non-exercise activity, or anything we do to move our bodies that isn't formal exercise such as walking to the coffee shop, stretching, standing, cooking, chores around the house, etc. It also includes more mild activity like fidgeting.
It is thought to have an important role in weight management, and can be responsible for up to 500 calories expended a day at its maximum.
How much sitting is too much sitting?
The increased risk of cardiovascular disease appears to emerge fairly consistently at between 8 to 10 hours of sedentary time a day.
In a large meta-analysis, researchers found that compared with the most active group (who sat <4 hours/day), those who sat the most (> 8 hours/day), had the highest risk of death. In another study, after adjustment for physical activity and other heart disease risk factors, high levels of sedentary time (>10 hours/d) was associated with an increased risk for cardiovascular disease.
Does exercising enough offset my risk of sitting around?
Importantly, the risk of prolonged sedentary time appears to be independent of time spent in formal exercise. This means that the risk associated with sitting for prolonged periods of time still applies to you even if you exercise regularly. So, you may not be off the hook even if you get in your 30 minute work outs every day.
One caveat. In the large meta-analysis cited above, individuals at the highest level of physical activity (ie 60-75 minutes of moderate to vigorous exercise a day) seemed to eliminate the increased risk of death associated with high sitting time. So if you’re exercising well above and beyond the guideline recommended amount a day, you may not experience adverse effects of prolonged sitting.
What happens to my body when I am just sitting around?
Several studies have shown worsening cardiometabolic parameters with high levels of sedentary time. Consistent with prior studies, one study found that when they measured sedentary time with accelerometers, prolonged sedentary time was associated with decreased HDL cholesterol, increased triglycerides, and worsening insulin resistance (increased fasting insulin, 2-hour glucose, and HOMA-IR). These findings were found even in those who met physical activity guidelines. The researchers postulated this may be due to the decreased uptake plasma triglycerides and free fatty acids by skeletal muscle during prolonged periods of sitting. Other studies have also found worsening of inflammatory markers like CRP.
So what should I do to decrease my risk of heart disease?
Although the evidence base is not quite as robust as it is for moderate- to vigorous-activity, guidelines recommend reducing sedentary time whenever possible. While it’s critical for our heart health to squeeze in the recommended levels of exercise a week, it’s also important that we try to construct our days such that we are moving our bodies in other ways as well.
One study found significant improvements in triglycerides and fasting glucose when participants shifted 2 hours of their day from sedentary time to standing; improvements were strengthened when participants further shifted those 2 hours from sitting to walking, with reductions in body mass index additionally seen.
Given that less of us are commuting to work, many of us are taking less steps a day and/or finding it less natural to move our bodies. In this context, ways you can increase your NEAT:
Get a standing desk. If this isn’t an option, take frequent standing/stretch breaks
Build in frequent breaks in your day to walk around the house or the block
Consider breaking up your day when possible for small errands. The dry cleaners in the morning, a walk for an herbal tea in the afternoon
Walking meetings
Pace while talking on the phone
If you are still commuting, walk or bike to work. Use the stairs. Park your car further from the store or office.
Let me know how it goes!
