Do Flexible People Live Longer?
This Week’s Research Highlight
Background
The link between aerobic fitness and survival has been long established in the scientific literature. People in the lowest quintile (bottom 20%) of aerobic fitness, determined via treadmill exercise testing, had a three-fold higher risk of death from all causes over an 8-year period, compared to those in the highest quintile.
Muscular strength, similarly, has emerged as a key factor in all-cause mortality in observational studies. Men in the lowest category of muscular strength were found to have a 1.5-2 times higher risk of dying from any cause, and this finding was independent of BMI, blood pressure, and aerobic fitness.
But one physical attribute that may be underappreciated with respect to long-term health is flexibility. Benefits of flexibility for survival are more subtle, and are only gradually starting to be unveiled.
Researchers in Rio de Janeiro previously found that the ability to sit and rise from the floor was a strong predictor of all-cause mortality. A low score on this simple functional assessment was associated with >6-fold higher all-cause mortality. In searching for physical attributes that might influence performance in the sitting-rising test, researchers subsequently determined that flexibility was a key predictor. Individuals who scored higher in an assessment of whole-body flexibility performed better at sitting and rising from the floor unassisted.
More recently, the same research team decided to directly investigate whether objectively measured flexibility was associated with lifespan. Let’s take a look at what they found.
Study
Brazilian researchers analyzed data from an ongoing cohort of 3139 participants, between the ages of 46 to 65, who underwent a medical examination, as well as a functional evaluation to assess their whole-body flexibility.
This was assessed using the Flexitest, which measures the range of motion of 20 joint movements in seven major body joints (2 in ankle, 2 in knee, 4 in hip, 3 in trunk, 2 in wrist, 2 in elbow and 5 in shoulder). Each movement is assessed on a scale of 0 to 4. When added together, a global score results, ranging from 0-80, which is known as the Flexindex.
This video shows what that assessment looks like, and below you can see a diagram of one of the joint movements and how it would be scored.
Participants were followed for an average of 12.9 years, and the researchers calculated how Flexindex scores were associated with risk of dying during the study period.
Rather than examine deaths from all causes, the researchers chose to restrict their analysis to natural and non-COVID mortality. This was done to exclude deaths that emerge from extraordinary circumstances, or from external causes that ostensibly would not be affected by physical flexibility.
Results
First of all, to no surprise, women were significantly more flexible than men: Flexindex was 35% higher in women, compared to men. Prior research examining the Flexindex has shown consistently greater scores for female than male participants, and this disparity only widens with age.
During an average follow-up of 12.9 years, 302 individuals (9.6%) comprising 224 men and 78 women died. Higher Flexindex scores were associated with lower mortality risk. In both male and female survivors, Flexindex was on average nearly 10% higher, compared to non-survivors.
After the researchers adjusted for age, BMI, and health status, they determined that men with a low Flexindex had a 1.87-times higher risk of dying during the follow-up period, compared to those with a high Flexindex. For women, a low Flexindex conferred a 4.78-times greater risk of dying due to natural or non-COVID causes.
Boring statistical side note: This apparent massive increase in mortality for inflexible women should maybe be taken with a grain of salt. The confidence interval for the hazard ratio for women was much wider than for the men (1.23-31.71 for women versus 1.50-2.33 for men).
This is probably because of the smaller sample size (only 1052 women in the study versus 2087 men) and much greater variation in flexibility scores within the female group.
As a result, there is less certainty about the estimated mortality risk for women, compared to men, and that 5-fold increase in mortality should be considered a less precise estimate.
In any case, the key takeaway here is that reduced body flexibility at midlife is strongly associated with higher mortality in middle-aged men and women.
Interpretation
A major strength of this study is that the researchers controlled for health status. Obviously, people who are critically ill are apt to be less mobile than healthier individuals.
Unfortunately, the researchers were not able to capture and control for variables related to physical activity. They did not have access to data related to past or current exercise habits, amount of sedentary time, or participation in sports or other activities.
Accordingly, I think these results must be treated with some skepticism. It’s not clear to me whether flexibility per se is responsible for the survival benefit observed here, or if flexibility might be acting as a proxy measure for physical activity and fitness. Generally speaking, if you move more, and challenge your body, you are going to be more mobile.
And this is likely to be even more critical among older individuals. As author de Araújo observed in a prior article:
"An interesting aspect is that the Flexindex value tends to vary more as the years go by, so that interquartile differences tend to increase in both men and women. This probably occurs, as with other human performance variables, due to progressively greater differences in the pattern of regular physical activity of individuals when they reach adulthood and in subsequent years."
People who exercise more experience an array of physiological adaptations, including greater joint mobility. But that specific one may not be playing a significant causal role in the remarkable reduction in mortality that we generally see in response to physical activity.
That having been said, stretching has been shown to have some intriguing health benefits, so cultivating flexibility may still be a worthwhile endeavor.
For example, stretching was shown to reduce tumor growth by 52% in mice that were injected with breast cancer cells. This was attributed to decreased levels of programmed cell death protein 1 (PD-1), a cell surface receptor that can obstruct the immune system from fighting cancer cells. Stretching also increased levels of specialized pro-resolving mediators (SPMs), which are cell-signaling molecules that play an important role in resolving inflammation.
Stretching is also surprisingly effective for modulating blood pressure. Older adults who were randomly assigned to perform a whole-body stretching routine on weekdays experienced significant reductions in blood pressure — surpassing another group who was assigned to perform moderate aerobic exercise. This is because when muscles are stretched, blood vessels also get stretched, which appears to reduce arterial stiffness and trigger the release of nitric oxide.
And of course, maintaining joint mobility is likely to be key for sustaining basic activities of daily living later in life, as the sitting-rising test demonstrated.
Random Trivia & Weird News
👸 Termite queens have the longest lifespan of any known insect — up to fifty years!
Termite queens are exceptional in many respects. Obviously, they are much bigger than other termite castes, often more than ten times as massive. They also control other members of their colony via chemical signaling, almost like something out of a sci-fi film: regulating their behavior and sexual development to ensure that the colony remains harmonious and functioning properly.
But perhaps the most intriguing distinction between termite queens and workers lies in their comparative lifespan. Worker termites normally only live around a few months up to perhaps a couple years. Meanwhile, termite queens can live for decades — remarkable not just among their own kind, but among insects in general.
This is particularly striking because termite queens are basically egg laying machines. They can produce thousands of eggs daily throughout their long lives. This challenges the typical trade-off observed in most animals, wherein higher reproductive output is linked to shorter lifespans.
Normally, energy invested in reproduction comes at the cost of somatic (body) maintenance, which in turn accelerates biological aging. But termite queens have somehow figured out how to reproduce prolifically while bypassing the molecular and cellular costs associated with reproduction. Perhaps research will unveil how they achieve this someday, and we can benefit in our own pursuit of healthspan and longevity.
Photo credit: Judith Korb
Podcasts We Loved This Week
- Venki Ramakrishnan: Why we age and how to slow it. Via The Proof.
- Claire Cain Miller: The parents aren’t all right. Via The New York Times Podcast.
Products We Like
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