Does spermidine actually do anything against ageing?

Spermidine helps cells clean themselves up, a process called cellular autophagy. This effect has been demonstrated in yeast, fruit flies, roundworms, mice and human cells, and the lifespan of all those organisms increased. In mice, dietary spermidine also protected the heart: less thickening of the heart muscle, better cardiac relaxation and healthier energy centres within the cell. That effect disappeared as soon as a specific autophagy protein was absent, showing that it works through this clean-up pathway.

In humans the evidence is still more indirect. A study of 829 participants followed over twenty years found that people who eat more spermidine die less often; the difference corresponded to the mortality risk of someone who is 5.7 years younger. Higher intake was also associated with lower blood pressure and fewer cardiovascular diseases. But these are associations, not proof of cause and effect. People who eat a lot of spermidine, through wholegrain cereals, legumes and fermented products, may live more healthily in several other ways as well. In addition, several authors of the positive mouse studies have a financial interest in a company developing spermidine extracts.

As a supplement, spermidine is available as a capsule or powder, usually derived from wheat germ; the label will say 'spermidine' or 'wheat germ extract'. No proven effective dose in humans has been established, and how long you would need to take it is likewise unknown. Which brand or form you choose makes no difference based on the available research. Because there are as yet no good comparative studies in humans, it cannot be recommended as a supplement; it is too poorly studied to say with confidence that a pill does the same thing as spermidine-rich food.

Getting more spermidine through your diet is a low-threshold and safe starting point. No concrete upper limits have been established regarding the safety of high doses.