Where is spermidine found?

Your body gets spermidine from three sources: your own cells, your gut bacteria, and the food you eat. Around two-thirds is produced internally, with the rest coming from diet. The richest food sources include wheat germ, natto, shiitake mushrooms, aged cheeses, and peas.

The challenge is that internal production declines with age, making dietary and supplemental sources increasingly important over time.

What causes spermidine levels to decline?

Studies measuring polyamine levels in blood and tissue have found that spermidine concentrations decline significantly from early adulthood onward. Several factors appear to contribute to this:

Age: the most consistent driver; cellular production slows as we get older

Diet: spermidine-rich foods are not always well represented in modern diets

Gut microbiome changes: the gut bacteria responsible for producing polyamines can become less active with age.

Reduced dietary diversity: a less varied diet provides fewer of the precursors needed for the body's own polyamine synthesis

This results in a gradual reduction in a compound that plays a central role in cellular maintenance.

The autophagy connection

Autophagy is your cells' essential renewal and recycling process that keeps your biology running as it should. It is one of the body's most important cellular maintenance systems, and the evidence for spermidine's role in supporting it continues to grow.

Autophagy slows with age. Its declining activity has been associated with a range of age-related changes, making the compounds that support it increasingly relevant as we get older.

Food derived vs. synthetic spermidine

The challenge of increasing your spermidine levels is consistency, quantity, and quality. The food-derived versus synthetic distinction matters here.

Not all spermidine is created equal. Food-derived spermidine has been part of the human diet for thousands of years and is backed by a growing body of human research, while synthetic spermidine has been studied mostly in animal models. The EFSA considers up to 6mg per day of food-derived spermidine safe, a guideline with no synthetic equivalent, meaning the majority of synthetic products are sold at unstudied doses.

Food-derived spermidine also occurs naturally alongside spermine and putrescine, two companion polyamines that work together in a recycling loop, a synergy synthetic versions lack. 

The polyamine recycling loop

Spermidine belongs to a group of compounds called polyamines. You may not have heard of them by name, but your body has been using them since before you were born. 

The three main polyamines in the human body are:

• Putrescine - a precursor that the body uses to produce spermidine
• Spermidine - the central polyamine with the strongest research backing for longevity support
• Spermine - a downstream polyamine that works alongside spermidine

These three don't operate in isolation. They exist in a dynamic recycling loop, converting into one another as your body's needs change. This is one reason why food-derived spermidine supplements offer advantages over isolated synthetic spermidine: the full polyamine matrix is present, as nature intended.