A Workout for Your Brain

In this article we dive into the fascinating connection between muscle health and brain function as explored in two recent narrative reviews by Oudbier et al and another by Sui et al. These studies highlight how physical activity influences myokine secretion—key signaling molecules from muscles that impact cognitive health. The review delves into the complex mechanisms linking muscle loss (sarcopenia) with cognitive decline, including inflammation, insulin resistance, and mitochondrial dysfunction. Learn how exercise not only preserves muscle mass but also supports brain health, offering insights into the importance of staying active for long-term cognitive well-being.

Unlocking the Muscle-Brain Connection

Recent scientific investigations have shed light on a compelling association between muscle health and cognitive function in older adults. A comprehensive review by Oudbier et al and another by Sui et al. delves into over a hundred studies to explore how the decline of skeletal muscle mass—known as sarcopenia—might be linked to the onset of dementia.

The Complex Relationship Between Muscles and Mind

While it's well-established that muscle strength and physical performance correlate with cognitive abilities, the precise mechanisms and direction of this relationship remain elusive. The review by Oudbier and colleagues seeks to unravel these complexities by examining four key physiological pathways that may bridge muscle deterioration and cognitive decline: systemic inflammation, insulin resistance, abnormal protein accumulation, and mitochondrial dysfunction. Topics you will no doubt hear me talk about more often than not in relation to health and longevity. 

Myokines: The Messengers Between Muscles and Brain

Skeletal muscles are not just for movement; they act as endocrine organs that secrete myokines—proteins and peptides that communicate with other body systems. Some myokines, like cathepsin B, can cross the blood-brain barrier and promote neurogenesis - the growing of new nerve cells. Others have anti-inflammatory effects that benefit both the body and the brain. For example, muscle-derived brain-derived neurotrophic factor (BDNF - another topic you’ll here me harp on about) supports the growth and maintenance of neurons and their mitochondria, essential for energy production and reducing oxidative stress.

Physical inactivity reduces the secretion of these beneficial myokines, potentially initiating a downward spiral of health effects. This reduction can exacerbate systemic inflammation, worsen insulin resistance, contribute to harmful protein accumulations, and impair mitochondrial function—all factors linked to cognitive decline and negative psychological states. 

A New Hypothesis on Causality

Based on these interconnected mechanisms, Oudbier et al. propose that muscle loss and lack of physical activity decrease myokine secretion, which then triggers a cascade of negative effects leading to cognitive decline. This hypothesis suggests that exercise isn't just beneficial—it's crucial for maintaining cognitive health. Physical inactivity doesn't leave you at a neutral baseline; it actively impairs essential physiological processes.

Evidence Supporting the Link

Most of the current evidence comes from epidemiological studies showing strong, consistent associations between low muscle mass and impaired cognition. While these studies can't prove causation, the addition of plausible biological mechanisms strengthens the argument. The review highlights that while muscle loss may lead to cognitive decline, the reverse might also be true—dementia could contribute to muscle deterioration through effects on motor function.

Figure: Three-Year Decline in Executive Function, by Muscularity. ALM = Lean Muscle Mass in the upper limb. 

The Takeaway

While further research is needed to fully understand these relationships, the message is clear: maintaining muscle mass through regular physical activity is likely vital for preserving cognitive function as we age. This isn't just about staying physically fit; it's about protecting your brain health.

For a deeper dive into this research, read the original review by Oudbier et al.: Linking Loss of Muscle Mass With Cognitive Decline: Is Inflammation the Underlying Mechanism? and the review by Sui et al. can be accessed here.