Chronic low-grade inflammation
A persistent, mild elevation of inflammatory signals in the blood that tends to rise with age.
Chronic low-grade inflammation describes a background state in which inflammatory messengers stay slightly elevated for months or years, rather than spiking briefly to deal with an injury or infection and then settling. It is usually invisible day to day and is detected on a blood test rather than felt as symptoms.
It matters because this state is associated with adverse health outcomes as people age, and researchers use it as one window onto biological ageing. Because it is a marker rather than a disease, changes in it are best read as a signal that something in the body's regulation has shifted, not as proof that illness has been prevented.
The usual measurements are C-reactive protein, a general marker produced by the liver, and cytokines such as interleukin-6, interleukin-10 and tumour necrosis factor alpha, which are signalling proteins released by immune cells. Trials of exercise, diet and sleep often report these markers because they respond over weeks to months, far faster than hard clinical outcomes.