Ghada Alsaleh still remembers the lab moment when the data first hinted at something remarkable: in a group of older adults whose immune systems were struggling to respond to vaccines, a simple daily supplement was lighting up their antibody production like a switch. The compound, spermidine—a natural molecule found in foods like broccoli, cheese, and lentils—was quietly doing something powerful in the bodies of people over 65 who had shown weak responses to three doses of a COVID-19 vaccine. As we age, our immune defenses weaken in a process called immunosenescence, leaving older adults more vulnerable to infections and less protected by vaccines. This vulnerability was stark during the pandemic, with over 92% of COVID-19 deaths occurring in those over 60. Even with vaccination, many older adults fail to produce strong antibody or T-cell responses, limiting protection. Researchers at NDORMS, led by Professor Katja Simon and Associate Professor Alsaleh, wanted to know if spermidine could help reverse some of this decline. In a pilot trial published in Aging Cell, 40 healthy adults over 65 were randomly assigned to take either a daily spermidine supplement or a placebo for 13 weeks after their third COVID-19 shot. The supplement proved safe and well tolerated, with no adverse effects. Crucially, about one-quarter of participants had shown poor antibody responses and clear signs of immune aging—such as DNA damage and cellular senescence—before the trial. Among this group, spermidine made a striking difference: it boosted antibody levels, strengthened B-cell activity, and improved the ability of antibodies to neutralize multiple SARS-CoV-2 variants. The team also found that spermidine reduced markers of cellular aging and stimulated autophagy, the body’s way of cleaning out damaged cells to keep the immune system running smoothly. “Our study suggests that biological aging of immune cells may be one reason why some older adults don’t respond well to vaccines, and that spermidine could help restore aspects of immune function in this group,” said Alsaleh. While the trial was small, its implications are large. If larger studies confirm these findings, spermidine could become a targeted intervention for older adults at risk of poor vaccine responses—potentially extending its benefits to flu and other vaccines. For now, the results offer a hopeful signal: the biology of aging may not be as fixed as we once thought, and nature might already hold some of the tools to help us age more resiliently.