Chronic inflammation is a sizable component of aging. The immune system becomes inappropriately overactive, disrupting its normal participation in tissue maintenance, and producing alterations in the signaling environment that change the behavior of other cells for the worse. Inflammation appears to be important in the age-related decline of stem cell activity, for example. It is certainly important in the maintenance of muscle tissue. The study here is far from the only one to show a link between chronic inflammation and the age-related loss of muscle mass and strength, a condition known as sarcopenia.
Skeletal muscle plays an integral role in maintaining homeostasis across organ systems. Skeletal muscle is plastic, changing dynamically in response to physical activity, load, injury, illness, and ageing. The age-related loss of skeletal muscle strength, muscle mass, and physical performance (sarcopenia), has been associated with falls and fractures in older populations, and remains a largely undiagnosed condition. Beyond ageing, sarcopenia is associated with age-related diseases such as dementia, chronic obstructive pulmonary disease, and cardiovascular disease. In older adults, several of these diseases coincide with decline in muscle mass and whether this is caused by ageing or disease is largely unknown. However, a common feature underlying both conditions is inflammation.
Chronic inflammation, characterised by higher systemic cytokine and acute phase protein circulation, is not only linked to ageing 'inflammaging' but also muscle mass loss. Tumor necrosis factor α (TNFα) released from diseased tissues has been shown to exert endocrine effects on skeletal muscle. In vitro studies have shown that TNFα is a key endocrine stimulus for contractile dysfunction in chronic inflammation and that the muscle derived reactive oxygen species (ROS) and nitric oxide (NO) participate in depressing specific force of muscle fibre, which can lead to muscle atrophy. Furthermore Interleukin (IL)-6, a key cytokine involved in low-grade chronic inflammation, has been shown to facilitate muscle atrophy via blunting muscle anabolism and energy homeostasis.
The aim of this systematic review and meta-analysis was to determine the relationship between systemic inflammation, muscle strength, and/or muscle mass in adults. Overall, 168 articles; 149 cross-sectional articles (n = 76,899 participants, 47.0% male) and 19 longitudinal articles (n = 12,295 participants, 31.9% male) met inclusion criteria. Independent of disease state, higher levels of C reactive protein (CRP), Interleukin (IL)-6, and Tumor necrosis factor (TNF)α were associated with lower handgrip and knee extension strength and muscle mass. Furthermore, higher levels of systemic inflammatory markers appeared to be associated with lower muscle strength and muscle mass over time.