Newsletter #299: Sedentary Time & Heart Health 🫀
We tend to think of heart disease as being an age-related condition. Something that people wrestle with as they get older. But that's really only because cardiovascular events, such as heart attacks, tend to occur later in life.
The truth is that the process of atherosclerosis begins far earlier than you might suspect. In fact, cardiovascular disease appears to start to take root in childhood.
This unsettling fact was initially recognized after an autopsy study conducted in hundreds of US soldiers who had been killed in action in Korea. These men were, on average, just 22 years old, yet more than 70% exhibited atherosclerosis in their coronary arteries.
Similarly, an examination of the aortas and coronary arteries of children who died in accidents revealed that more than half had lesions in their artery walls.
These discoveries suggest that if we want to prevent heart attacks and strokes later in life, we ideally would want to start as soon as possible. So what can we do to set kids up for good cardiovascular health for life?
Well, for one thing, physical activity is known to play a role in heart health, and our awareness of this relationship also goes way back, more than seventy years, to the classic epidemiological research of the late great Jeremy Morris.
Morris started to follow rates of coronary events in transit employees in London. He compared two professions: bus drivers and conductors. These men were similar socioeconomically, but had different levels of physical activity during their work shifts, as you might imagine. He found that the conductors had fewer than half as many heart attacks as the drivers.
With all of that in mind, a study was just published about six weeks ago that examines how different levels of physical activity (or the lack thereof) influence markers of cardiovascular risk in children as they enter adolescence and early adulthood. Let's take a look at what was found.
This Week’s Research Highlight
Less sedentary time and more light physical activity substantially reduces cardiovascular risk in children.
Epidemiologist Andrew Agbaje analyzed data from 792 children from a UK-based birth cohort. These individuals provided objective measures of their physical activity and sitting time via wrist-worn activity trackers on multiple occasions at the ages of 11, 15, and 24 years. The participants also underwent repeated blood work during clinic visits at these ages, in order to assess the relationship between their activity patterns and biomarkers of cardiovascular risk, such as LDL cholesterol.
Let's start by looking at how activity patterns evolved in these young people.
Over the course of 13 years, their moderate-to-vigorous physical activity stayed pretty stable, at around 50 minutes per day.
Meanwhile, levels of light physical activity decreased from 6 hours per day down to 3 hours per day. (“Light physical activity” basically encompasses anything that is less intense than a brisk walk, like standing, performing chores, etc.) Sedentary time concomitantly increased from 6 hours per day up to 9 hours per day.
In general, participating in more physical activity was associated with lower levels of cholesterol. However, gaining body fat (which is not uncommon when going from age 11 to 24) dramatically attenuated the beneficial effects of moderate-to-vigorous physical activity.
Increased light physical activity, in contrast, was not strongly mediated by fat mass, and had a 5- to 8-fold total cholesterol-lowering effect. On the opposite end of the spectrum, increased sedentary time contributed nearly 70% to the total rise in cholesterol observed between childhood and young adulthood.
So at first, the fact that light physical activity has a far more robust impact than more intense exercise seems pretty counterintuitive.
But if we go back to the work of Jeremy Morris, one could argue that seminal research is more of an illustration of the comparative impact of sitting versus standing/light activity — rather than the power of exercise per se.
Recall that the bus drivers were quite sedentary, sitting for most of their shifts, while conductors were on their feet for most of the day. But the conductors weren't engaging in moderate-to-vigorous physical activity. They were standing and walking up and down the aisles, and occasionally climbing stairs in double-decker buses. Indeed, this is evident in the average heart rate of the conductors during their work shifts, which was just 106 bpm, compared to 91 for the bus drivers.
More recent analyses suggest that time spent sitting has been found to be associated with increased mortality — including cardiovascular disease — and this is independent of exercise.
I think the simplest explanation for the greater lipid-lowering impact of light activity has to do with the amount of time that it can consume, and the extent to which it can displace sedentary time.
Moderate-to-vigorous exercise only takes up less than an hour, while sitting and light physical activity both occupy major chunks of the day. If we look at the patterns of activity in the subjects, we see that light physical activity and sedentary time appear to exist in opposition to one another in this study — as one increases, the other decreases. That makes sense, because if you're not sitting down, you're likely participating in some sort of light physical activity.
The key takeaway here is that if you want your kids to experience optimal cardiovascular health for life, it's smart to get them up and moving throughout the day, not just during sports or other structured activities. (Research in adults suggests that it is probably a good idea for the rest of us too!)
Random Trivia & Weird News
Contrary to popular belief, bats are not blind. However, they are nocturnal creatures, which means they often have to navigate and hunt in complete darkness. They pull this off via echolocation. Basically, bats emit lots of high-frequency sounds as they are flying. As these ultrasonic waves bounce off of objects, they create echoes, which the bats use to build a mental map of the world around them. This adaptation enables them to find food sources, such as insects, that would normally elude them in darkness.
However, some of their would-be prey have adapted in turn.
Certain species of tiger moths produce clicks at an extraordinary rate (as much as 4500 times per second). These clicks interfere with the echoes, making it extremely difficult for the bat to figure out where the moth is. Field studies have shown that this jamming lowers capture success by as much as 10-fold.
Podcasts We Loved This Week
- Stuart McGill: Lower back pain — causes, treatment, and prevention of lower back injuries and pain. Via Peter Attia.
- Ed Yong: Expanding our umwelt — understanding animal experiences. Via Science Friday.
Products We Like
As we enter February, most of us in the Northern Hemisphere haven’t been seeing quite as much sunshine for a while now. At this time, making sure that you’re getting your vitamin D is paramount.
Vitamin D seems to work synergistically with vitamin K2, so it makes a lot of sense to supplement them together. I’ve used this product for several winters now. It’s an inexpensive supplement, and Zhou’s products are lab-tested to ensure that you’re actually getting what you paid for.
humanOS Catalog Feature of the Week
In this course, we:
- Examine how physical activity is defined and measured
- Explore the physical activity of our ancient ancestors and modern day hunter-gatherers, to get a sense for “natural” patterns of physical activity for which we evolved
- Look at how physical activity and fitness affect health and lifespan
- Review the key components of a smart activity program, so you can get the right dose of physical activity for you!
Wishing you the best,