Does spermidine actually do anything against ageing?
Animal research and population studies provide indications that spermidine can slow ageing processes, but evidence from randomised trials in humans is still largely absent. It is too early to recommend a supplement, but eating spermidine-rich food is at least harmless.
Spermidine is a substance that occurs naturally in your body and is also found in food, such as wheat germ, mushrooms and cheese. Its concentration declines as you get older, and lower levels are associated with more age-related conditions. Whether that decline is a cause or a consequence has not yet been established in humans.
The most solid evidence concerns the mechanism: spermidine stimulates cells to undergo autophagy, the process by which damaged material is cleared away. This has been demonstrated in multiple organisms and cell types. If you block that clean-up process, the protective effect disappears. Animal experiments also show that spermidine extended lifespan in yeast cells, fruit flies, roundworms and human immune cells in the lab, and that in mice it preserved heart function at older ages and reduced oxidative damage.
In humans the evidence is still indirect. Large population studies show that people who obtain more spermidine through their diet have less cardiovascular disease, less cognitive decline and lower mortality from cancer and cardiovascular disease. These are associations, not proven causes: people who eat a lot of spermidine-rich food may also live more healthily in other ways.
Randomised trials in humans, in which participants are randomly assigned a supplement or a placebo, are scarce at this point. Studies are under way, but completed results are largely lacking. If you want to use spermidine as a supplement, you therefore do not yet know whether the effects seen in animal research will also occur in you, or at what dose.
All claims are based on reviews and lab/animal research (PMID 19801973, 24481223, 27841876, 30306826, 33852843, 37004845, 37326367, 38181790). Human evidence is limited to observational population studies; randomised trials in humans have not yet been completed.
Does taurine work against ageing?
Taurine supplements have not yet been proven as an anti-ageing intervention in humans. The animal results are promising and mechanistically supported, but clinical trials in humans are still entirely absent.
Does taking resveratrol make sense as an anti-ageing strategy?
For humans there is no convincing evidence that resveratrol supplements do anything against ageing; the animal research is interesting but has not yet translated into clinical practice, so hold off on supplements until better human data are available.
What do we really know about metformin and ageing?
Metformin may extend your healthy years by helping to prevent disease, from diabetes to heart and vascular disease. Whether it also slows ageing itself in people without diabetes is for the TAME trial to show, the first large study to test that directly. If you are considering it for that reason, expect stomach and bowel complaints and a falling folate level.
What do we know about rapamycin as an anti-ageing agent in humans?
Rapamycin shows early positive signals in humans for immune function and skin, but long-term safety is unknown and side effects such as infections and unfavourable blood lipids are a real risk. Use outside a clinical trial is premature.
Do multivitamins help with healthy ageing?
Daily multivitamins appear to offer modest protection for older adults' memory, but for most other aspects of healthy ageing the effect is small or absent. If you have a confirmed deficiency in vitamins or minerals, supplementation is certainly worthwhile; do not regard it as a wonder remedy.
Does quercetin work against ageing and inflammation?
Quercetin shows promising signals in the laboratory and in animals, but in humans there is not yet solid evidence. Taking supplements on the basis of this early-stage research gets too far ahead of the science.