How to Offset the Effects of Sitting too Much

Doctor: You spend too much time sitting.

Patient: I understand.

Doctor: Exactly.

That's not the dumbest joke I know, but it's close.

Our hypothetical patient should be asking the doctor some questions. In particular: How much sitting is bad for my health? And: What's the best way to offset the effects of sitting too much?

This newsletter is prompted by new data that addresses both questions. It's also a reflection on how to bridge the gap between scientific data and practical need. We need concrete answers to these questions, but extracting guidance from the data can be tricky.

Why is this important?

Health experts never stop warning us about the perils of a sedentary lifestyle. Study after study has linked physical inactivity to health problems ranging from cardiovascular disease to obesity and premature death.

The source of these problems may be sitting rather than other forms of sedentariness. A 2020 study showed that the Hadza, a hunter-gatherer society in Tanzania known for good cardiovascular health, are just as sedentary as we are. (Americans average about 9.5 hours of sedentariness per day; among the Hadza, it's 9.9 hours.) But here's a key difference: The Hadza often squat, or kneel, or assume other postures that require much more lower limb muscular activity than just sitting in a chair.

Meanwhile, we have desk jobs and easy chairs and couches and Netflix and countless other reasons for sitting with little muscular activity other than typing or operating a remote. So, we might want to ask: How much sitting is problematic, and what should we do to counteract the effects? (I'll be addressing the latter question first. Spoiler alert: I'm not going to recommend squatting.)

A new study

I want to focus on one of the better-designed health studies I've encountered in recent months. This study, currently in press at Circulation, was led by Dr. Joanna Blodgett at the Institute of Sports Exercise and Health in London.

Blodgett and her team looked at how blood pressure is affected by six behaviors:

• sleeping

• sedentary behavior (sitting or reclining)

• standing

• slow walking

• fast walking

• exercise-like activity

("Exercise-like activity" includes conventional exercise as well as mildly strenuous behaviors like climbing stairs.)

Blodgett and colleagues obtained data for 14,761 adults. In theory, the researchers could've asked each participant how much time they spent each day sleeping, sitting, etc. The actual approach to measurement was more careful. For a seven-day period, day and night, each participant wore something called an accelerometer taped to one thigh.

An accelerometer is a small device that records changes in the speed and direction of movement. Although not infallible, a thigh-mounted accelerometer can reliably distinguish between the six behaviors bullet-pointed above.

The purpose of the study was to see how the amount of time spent per day on each behavior was related to changes in systolic and diastolic blood pressure, as measured at the beginning and ending of the seven-day period.

—Systolic blood pressure (SBP) is the highest pressure in your arteries when your heart beats. This is the first number in a blood pressure reading (e.g., the 126 in a reading of 126/82).

—Diastolic blood pressure (DBP) is the pressure in your arteries when your heart rests. This is the second number in a blood pressure reading.

Main findings

Here's how the Washington Post summarized the findings:

That's not a bad summary, but there's more good news – and some grounds for caution – that ought to be shared.

Recall that six behaviors were recorded in this study: sleeping, sedentary behavior (sitting or reclining), standing, slow walking, fast walking, and exercise-like activity.

Blodgett and colleagues treated these behaviors as comprehensive and exclusive. That is, they assumed that at any moment of the day, a person will be engaged in one and only one of them. This enabled something called reallocation analyses, or estimates of what would happen if a person spent more time doing any one behavior as opposed to the others.

Here are some of the main findings:

• Systolic blood pressure (SBP) improves significantly with 5 more minutes per day of exercise-like activity. The largest improvement occurs when exercise-like activity replaces sedentariness.

• SBP improves by 2 mmHg when exercise-like activity replaces any one of the other behaviors for just over 20 minutes per day. This would mean, for instance, that after a week, resting blood pressure would drop from 124/80 to 122/80.

• Diastolic blood pressure (DPB) improves significantly when 5 minutes of exercise-like activity per day replaces 5 minutes of sedentary activity.

• DBP improves by 1 mmHg when exercise-like activity replaces any one of the other behaviors for around 10 to 15 minutes per day.

In the Appendix, I dive a bit more deeply into the findings, and I include some comments shared with me by Dr. Blodgett and an independent expert about the meaning of the data. The bottom line is good news: Just a little bit of additional activity each day can lower your blood pressure.

Some cautions

1. Type of activity matters.

The healthiest alternative to sitting isn't merely getting up.

For instance, Blodgett and colleagues found no meaningful benefits for standing. One of her co-authors, Matthew Ahmadi, published a study last month that drew similar conclusions. (In fact, Ahmadi's data suggests that standing more than 2 hours per day increases the risk of orthostatic circulatory problems like hypotension and varicose veins.) Thus, a standing desk is not in itself a solution to the problem of sitting too much.

Blodgett's data also didn't show much benefit of walking. Other studies concur that walking a little more each day wouldn't be helpful. You'd either need to walk substantially more, or engage in 5 minutes of light walking following every 30 minutes of sitting.

In short, what's needed every day is a bit more exercise, or "exercise-like activity", whether that means climbing stairs or joining your kid at the playground or rearranging a closet.

2. Increasing exercise may by offset by compensation effects.

Studies show that when people start exercise programs, they may unconsciously reduce the frequency or intensity of non-exercise activities. A person starts doing YouTube cardio workouts; their walks in the park then become shorter and less frequent.

If the new data inspires you to exercise 5 minutes more per day, you have to make sure to replace sedentary behavior without slacking off in other areas. Simply exercising more isn't enough.

3. Exercise doesn't necessarily offset the effects of excessive sitting.

A recent study showed that after sitting more than 13.5 hours per day for four consecutive days, one hour of vigorous treadmill work created no metabolic changes. It's as peoples' bodies had become "resistant" to the expected benefits. Another study found diminishing benefits of exercise after 11 to 12 hours of sitting per day. The implication is that you can't count on physical exercise to offset the effects of excessive sitting.

Of course, sitting too much has other physical downsides, ranging from lower back pain to gluteal amnesia, or "dead butt syndrome" (which is not quite as horrifying as it sounds, but still…nobody would want it). If you're glued to a screen for work and/or play, you may be contending with other issues ranging from eye strain to repetitive stress injuries – all good reasons to get up, look away, and move around.

Two takeaways

1. How much sitting is too much?

I know you want a number. I will give you one. But I want to stress that it's going to be a crude estimate. You can't take the findings of observational health studies too literally. Measurements tend to be imprecise. The same study, conducted with a different sample, would yield different estimates. And no study can capture all the distinctions shown to be relevant in other research. For instance, Blodgett's "exercise-like activities" gloms together all sorts of things, while other studies show distinctions between the benefits of, say, light as opposed to vigorous exercise.

Having said all that, recent data from independently-run studies shows risks of impaired cardiovascular, neurological, and cellular health beginning at around 10 hours of sitting per day. Beyond that point, the more one sits, the greater the risk.

This is not to say that if you sit that much, you should worry. The increased risk with each additional hour of sitting per day (or some equivalent) is relatively small. Moreover, estimates of risk are generalizations about groups of people that don't guarantee what will happen to individuals. If you move to a city with a high crime rate, you may never personally experience a crime.

The best thing you can do, if you don't want to be a crime victim, is to take steps to avoid becoming one. In the same way, if you're sitting 10 hours per day or more, you can take steps (literally) to mitigate risk. I recommend that. Meanwhile, there's no benefit to sitting around (literally) and wondering if you're sitting too much.

2. What's the best way to offset the effects of sitting too much?

The data suggests that if you sit for long periods of time, two strategies can help:

(a) Periodic breaks, during which you move around rather than merely standing (e.g., 5 minutes of walking following each 30-minute period of sitting).

(b) Regular exercise. For instance, the CDC recommends 150 minutes of moderate-intensity exercise per week, including 2 days in which the focus is on building muscular strength.

The CDC recommendation translates into just over 21 minutes of exercise per day, or half an hour 5 days a week. This feels like a lot if you're busy, but it's likely good for you. Blodgett's data indicates benefits for blood pressure after just one week. A study published this September showed that adults who exercise vigorously for half an hour per day have cholesterol levels (TC/HDL ratios) comparable to sedentary people who are 5 years younger, as well as BMIs comparable to those of sedentary people 10 years younger. Again, don't take the specific numbers too seriously. I doubt you'd lose any benefits by exercising 29 as opposed to 30 minutes per day.

(I practice what I preach, but not necessarily because I preach it. I've been an endurance runner for over three decades, and the older I get, the more creaky my legs feel if I sit for long periods without taking frequent breaks to stretch or walk around. Also, whenever possible, I try to combine screen time with exercise. I'm starting to forget what John Oliver looks like upright, because I typically see him in the midst of doing planks or leg lifts.)

Thanks for reading!

---

Appendix: Statistical significance, clinical meaningfulness, and more good news

One of the appealing things about the Blodgett et al. study is that the researchers explicitly distinguished between statistical significance and clinical meaningfulness. Health researchers often fail to do this.

A statistically significant finding is one that's considered unlikely to be due to chance, but significant findings aren't necessarily meaningful. If a thousand people take a weight loss drug for one year and every person loses an ounce, the drug may be found significantly more effective than a placebo – the drug really does reduce weight – but the benefits are meaningless. Losing an ounce per year won't translate into health benefits or even be noticed.

Blodgett and colleagues found that over the course of a week, 5 extra minutes of exercise-like activity would reduce both blood pressure variables by approximately half an mmHg. So, for instance, 129/78 would become something like 128.5/77.5. The researchers were careful to distinguish this statistically significant finding from clinically meaningful ones, such as improvements in blood pressure resulting from an extra 15 or 20+ minutes per day in exercise-like activities.

Still, they framed that significant, half-an-mmHg change in positive terms. As Blodgett told the Washington Post, "any difference helps."

I found this a little confusing – isn't anything that benefits your health clinically meaningful? – and so for clarification I reached out to Dr. Blodgett as well as to Dr. Naveed Sattar, a professor of cardiometabolic medicine at University of Glasgow.

In her email to me, Dr. Blodgett implied that what's clinically meaningful is what would be noticed in a clinical setting:

"A statistically significant difference can sometimes be negligible and not noticeable at a clinical level. That’s why we aimed to demonstrate both aspects..."

I take this to mean that because blood pressure readings are expressed as whole numbers, a change of half an mmHg isn't clinically meaningful because it won't be detected. (If you're a math person, you can imagine scenarios in which that's not literally true, but there's no value here in splitting hairs or BP readings.)

Dr. Sattar agreed that the small change in blood pressure accruing from the extra 5 minutes of exercise-like activities would be beneficial, while adding that you'd have to continue engaging in the activities to continue reaping the benefits. As he put it,

"any reduction [in blood pressure] if maintained, will reduce risk long term.... And so, key is for people to develop new sustainable habits to include...more activity."

In short, it looks like a little bit of extra activity is a good thing, particularly for folks with higher blood pressure, given the clear connections between high blood pressure and cardiovascular disease, strokes, and other health problems.

Although studies linking blood pressure reductions to improved health often look at larger increments of change (e.g., 5 mmHg), the effects appear to be continuous – a point that Dr. Sattar mentioned in his email to me – which is to say that every little bit helps.