Older female mice given semaglutide lived 92 days longer; they were not followed for life against mice eating the same reduced amount of food
Older female mice given semaglutide lived 92 days longer; they were not followed for life against mice eating the same reduced amount of food
On September 2, Nature published a study of 79 twenty-month-old female mice: 40 received semaglutide daily, while 39 received control injections of saline, a salt solution without the drug. Median lifespan, the age by which half of each group had died, was 834 days in the semaglutide group and 742 days in the control group. Semaglutide reduced food intake by 24%, so interpreting the 92-day difference depends on the study design.
The 92-day difference came from comparing two daily regimens: semaglutide and saline. Semaglutide suppresses appetite, and calorie restriction can itself extend lifespan in mice. A lifelong group eating the same 24% less food would have allowed the researchers to measure how much of the difference was associated with the drug and how much with the reduced food intake.
Gerontologist Martin Borch Jensen raised this specific question: why did the study include a calorie-restriction comparison but no lifespan curve for mice with matched food intake? In a follow-up, he describes the difference as notable but considers the “+12%” figure premature as an estimate of the drug’s own effect, because both the treatment and the amount of food changed in the experiment. The authors separately compared semaglutide with 24% calorie restriction in a five-month group. Mice in these two groups ate the same amount of food, and the researchers assessed movement, memory, and the body’s response to glucose. The lifelong 92-day figure came from a different pair of groups.
In the lifelong part of the experiment, both groups received daily injections. A separate group receiving no injections would have allowed the researchers to measure how repeated procedures affected baseline survival. A subsequent lifelong experiment with matched food intake and a no-injection group could separate the contributions of the drug, reduced food intake, and daily injections.