Why Do We Feel Stiff in the Morning? Blame Biological Clocks

Your biological clock doesn’t just control when you fall asleep. It may also regulate inflammation in the body. New research on the cells from the joint tissue of humans and mice found that the circadian rhythm helps repress inflammation during the night. The study, conducted by University of Manchester biologists, was published by the Federation of American Societies for Experimental Biology (FASEB) in the FASEB Journal. 

The study, focused mainly on chronic inflammatory diseases like rheumatoid arthritis, found that mice with arthritis (which had been induced by collagen injection) showed different amounts of swelling as the day went on. The mice were kept in a windowless container where the researchers could precisely control the light. They found that six hours after the lights went on, the mice’s paws were significantly more swollen than they were in the middle of “nighttime” in the habitat, when inflammation was at its lowest. Certain cells in joints, called fibroblast-like synoviocytes (FLS), have a 24-hour clock that dictates the body’s response to inflammation.

When the researchers studied mice who had been genetically altered to lack a gene involved in these cells’ biological clock mechanism, the mice’s joints were more inflamed, and the inflammation didn’t go down during the night as before. When they administered a drug designed to activate the proteins (CRYPTOCHROMES 1 and 2) created by that clock-related gene, it protected against inflammation.

The researchers also tested human FLS cells to ensure that they, too, had a circadian rhythm, although obviously they didn’t tamper with human genes to further their analysis, as they did with the mice.

The study not only suggests that there could be new ways of targeting inflammation with drugs, but also that timing when patients with chronic inflammation take their drugs might make a major difference. And even for those of us without rheumatoid arthritis, joints’ biological rhythms still affect our lives. As your body stops suppressing inflammation—as you wake up in the morning—you start to feel stiff, explaining why you want to stretch so much in the morning.

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