Semaglutide Extends Lifespan in Older Mice, Outperforming Calorie Restriction on Some Measures

This is mouse research, not a human trial. The team, led by Danica Chen at the University of California, Berkeley, worked with female C57BL/6 mice that were 20 months old, which is late in a mouse's life. The mice received a daily injection of either semaglutide or a vehicle (an inactive control). The study text we reviewed does not give the number of animals per group, so we cannot report it here.

Why compare the drug with dieting? Calorie restriction, eating less without malnutrition, is one of the best-studied ways to slow ageing and extend lifespan in animals. The authors note it is hard to keep up. They set out to test whether a GLP-1 drug could act as a "calorie restriction mimetic", meaning something that captures its benefits without the diet.

The lifespan result came first. In the group treated for the rest of their lives, median lifespan was 834 days with semaglutide, against 742 days for controls. That is a gap of 92 days. The causes of death were similar in both groups. The authors say death was delayed across several categories unrelated to tumours, which fits a broad slowing of age-related decline.

A separate group was treated for three months and tested. Semaglutide cut food intake by 24%. The weight lost came mostly from body fat, with a higher share of lean mass. Treated mice moved and explored more in a new environment, did better on a memory maze, and performed better on balance, grip and treadmill tests. After adjusting for body weight, the grip result held. They also cleared blood sugar more effectively.

Tissue and gene analyses pointed the same way. Treated mice showed lower inflammation, fewer markers of cellular senescence (ageing cells that stop dividing), less DNA damage and better signs of mitochondrial function. Blood stem cells looked younger, and the brain region involved in memory showed more new neurons. Gene activity changes overlapped with those seen under calorie restriction, including lower inflammation and lipid-metabolism signals.

The direct comparison matters most for scientific relevance. In a longitudinal test against matched calorie restriction, semaglutide preserved baseline function and copied many of the diet's benefits by limiting age-related decline. It also produced gains above baseline, and better trajectories than the diet, in exploratory drive, spatial memory and glucose control. According to the ScienceDaily coverage, the mice were compared over five months, and metabolic rate stayed largely unchanged on the drug while it slowed on the restricted diet. The authors conclude the drug has effects beyond those explained by eating less.

Chen, quoted by ScienceDaily, said these differences "point to the possibility that GLP-1 drugs tap into a biological pathway independent of calorie restriction." Rafael de Cabo of the National Institute on Aging, who wrote a commentary, said that if these drugs slow ageing, "a wide range of clinical benefits is exactly what you'd expect to see." The NIH funded the work, according to the coverage.

Humans are a different matter. The study used only female mice, and the results do not show that these drugs extend human life. One early human signal comes from a small, separate study in npj Aging. It was a post hoc look at 41 people with HIV and fatty liver disease who took semaglutide for 24 weeks, with no control group. Across the group, the epigenetic ageing measures did not clearly improve. For example, the median change in the DunedinPACE pace-of-ageing score was slightly upward. Those whose score fell had greater liver fat reduction (p = 0.024). The authors call the results exploratory and say the group-wide changes cannot be attributed to the drug.

For now, the takeaway is modest. The mouse data suggest the benefits of GLP-1 drugs may go beyond weight loss and beyond simple calorie cutting. Whether that holds in people, and in healthy older adults without obesity or diabetes, is untested. Chen told ScienceDaily that future clinical studies may look at that group. Watch for those trials, and for work in male animals, which will show how far these results can be pushed.

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