Does Spermidine delay aging in humans?

Spermidine is a polyamine, and plays an essential role in cell growth, proliferation and renewal. But as we get older, our natural levels of spermidine decrease, reducing the ability of our cells to renew and repair themselves.

About one third of the spermidine level in the body is produced by our own cells, the rest is absorbed through the food we eat and certain bacteria found in our digestive tract. Originally isolated from semen, there are a variety of dietary sources of spermidine including grapefruit, soy products, legumes, corn, whole grain, chickpeas, peas, green peppers, broccoli, oranges, green tea, rice bran, and fresh green pepper. It can also be found in shitake mushrooms, amaranth grain, wheat germ, cauliflower, broccoli, and a variety of mature cheeses, and durian.

It is worth noting that much of the Mediterranean diet contains spermidine rich foods. This may go some way to explain the phenomena of “blue zones” and why people there often live longer than elsewhere.

We begin to age on a cellular level. Spermidine is crucial in the process of cell renewal because it increases autophagy, which removes damaged proteins from cells. Autophagy (ancient Greek for "self - (auto) eating (phagein)") is a cell recycling process in which cells break down damaged or unusable cell components and generate energy as a result. Damaged cell components contribute significantly to the development of age-related diseases, so the use of aged cell components in this way keeps the cell fresh and healthy.

Autophagy is therefore essential for the protection against diseases and can help inhibit the aging process. A 20-year-long study at the University of Innsbruck found that eating more spermidine-rich foods correlated with a 5-year increase in life expectancy and lower overall mortality.

Recent epidemiological evidence suggests that increased uptake of spermidine with food also reduces overall cardiovascular, by protecting against artery-blocking plaques and cancer-related mortality in humans. It may even improve vaccine protection in older adults.

Studies also suggest spermidine may help prevent memory loss and slow cognitive decline because it has a neuroprotective effect against the damage caused by inflammation and oxidative stress. A 2018 study found that older adults who took spermidine daily saw a significant improvement in memory and cognitive performance. Autophagy also helps clear out toxic proteins linked to neurodegenerative diseases such as Parkinson‘s and Alzheimer‘s.

Polyamines like spermidine were originally relevant to cancer research because of their role in cell proliferation and growth. Disturbance of polyamine metabolism was observed in several types of cancer, including skin, breast, lung, prostate, and colon. However, more recent cancer research studies have focused on spermidine as a caloric restriction mimetic (CRM). CRMs are molecules that limit cancer cells’ access to nutrients, thus making them more vulnerable to anti-cancer treatments. As an autophagy activator, spermidine therefore also has potential for both cancer prevention and treatment, especially to limit tumour growth.

A balanced diet, especially one rich in fruits and vegetables, can help maintain high levels of spermidine, but it is also available in powder or tablet form as a supplement, usually containing natural spermidine from wheat germ extract.