Newsletter #304

Surveys have suggested that Americans spend as much as 13 hours of their waking day sitting.

This is obviously not ideal.

A pile of epidemiological evidence indicates that sitting for long periods of time is linked to greater risk of cardiovascular disease and mortality. For instance, one meta-analysis of 18 studies found that the highest levels of sedentary behavior were associated with 147% higher risk of cardiovascular disease and 90% higher risk of dying from heart disease.

On the other hand, accumulating more steps per day is associated with significantly lower mortality risk. When researchers followed more than 2,000 middle-aged adults for about eleven years, they found that people who got at least 7,000 steps per day had a 50%-70% lower risk of mortality during the follow-up period..

So far, this sounds straightforward and consistent — sitting a lot is bad, and walking more is good.

But what complicates the interpretation of all of this research is that relatively high levels of sedentary time and relatively high doses of walking are actually not mutually exclusive. In other words, a given individual can have a lifestyle that exhibits both simultaneously. Indeed, it is a pretty common pattern nowadays for knowledge-based workers to sit for 8-10 hours per day, but also engage in long bouts of walking, as well as structured exercise. I bet a lot of you fit this profile!

However, most studies that have assessed the impacts of sedentary behavior and physical activity look at them separately, and are not designed to investigate how they relate to or influence one another.

So, can higher levels of movement (in the form of steps) effectively counteract negative effects of prolonged sitting?

Researchers in Australia recently tried to tackle this question.

We know that accumulating more daily steps is health promoting. However, it remains unclear whether and to what extent these effects are modulated by sedentary time.

Researchers affiliated with the University of Sydney's Charles Perkins Centre analyzed data from 72,174 participants in the UK Biobank. These individuals had worn accelerometers for at least seven days to objectively measure physical activity — capturing both their daily step count and the amount of time that they spent being sedentary.

In these subjects, the median sedentary time was 10.6 hours. Accordingly, the researchers split participants into two groups based on this median, classifying those who were sedentary for more than 10.5 hours per day as having high sedentary time, and those who spent less than 10.5 hours per day as having low sedentary time. Participants were followed on average for about seven years.

To see how these behaviors influenced long-term health outcomes, the research team referred to hospital records and death registries for data on cardiovascular disease and mortality respectively.

First, the researchers took the bottom fifth percentile of daily steps (2200 steps) and used that group as a comparator for all other levels. They found, unsurprisingly, that any amount of daily steps above 2200 per day was linked to lower risk of CVD and risk of dying during the study period.

The optimal dose for lowering both cardiovascular disease and mortality occurred somewhere between 9,000-10,500, and this was largely true across both high sedentary and low sedentary groups. This was linked to a reduction in mortality risk of 39%, and lowered cardiovascular disease incidence by 21%.

There were, nevertheless, some slight differences between the groups. For instance, the high sedentary group enjoyed somewhat greater relative reductions in mortality in response to an equivalent number of steps, which perhaps lends support to the notion of compensation.

As the researchers explain: "Our findings emphasise the importance of increasing daily steps particularly among adults who are highly sedentary. In the high sedentary time group, the stronger association could be attributable to the more pronounced impact of daily step accumulation in individuals who are at a higher risk of mortality from the adverse effects of sedentary time."

Finally, if you're not able to achieve the "optimal dose," don't sweat it too much: about half of the benefits for cardiovascular disease and dying from any cause was achieved in those who got between 4,000-4,500 steps per day.

One of the reasons why we are so sedentary, obviously, is because of the transformational innovations of the past 150 years, such as automobiles, labor-saving appliances, and other modern conveniences. In other words, we sit around more because we can — and because changes in the economy incentivize it.

The Old Order Amish, however, remain committed to a pre-industrial lifestyle. Studying their activity patterns grants us a window into the way that our ancestors might have lived.

When researchers equipped 98 members of the Old Order Amish with pedometers to gain insight into their physical activity patterns, the results were eye-opening. The men got on average 18,425 steps per day, and the women accrued 14,196 steps daily. This was accompanied by 3.4-10 hours per week of vigorous physical activity, and around 40 hours of moderate physical activity weekly.

Notably, just 9% of the women, and 0% of the men, were obese.

Even on their least active day – their day of rest, so to speak — the Amish were still getting close to 10,000 steps!

If you’re trying to increase your step count, a tracker of some kind is essential. Fitbit is a perennial favorite in this space, and it is one that we continue to rely upon here.

(And of course, you can easily sync your Fitbit data to your humanOS Dashboard for a more complete view of your activity patterns over the course of time).

In this course, we:

Wishing you the best,

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