A little zinc late in life helped old worms keep making proteins, and live a few days longer

Every cell depends on proteins, and keeping them in good shape is a full-time job. Cells build proteins on ribosomes, molecular machines that read genetic instructions, then fold them, repair them and break down the damaged ones. With age this system frays: proteins misfold and clump together, which is a hallmark of aging and of diseases such as Alzheimer's.

Zinc is a trace metal that many proteins need to hold their shape. Ribosomes are among the biggest users: several of their parts grip a zinc atom. Older people are often short of zinc, which has mostly been studied for its effects on the immune system. This study asked a different question: does losing zinc with age harm the protein-making machinery itself, and does giving it back help?

The work was done in C. elegans, a roundworm about a millimetre long that lives only a few weeks and is widely used to study aging. It is a preprint, so it is not yet peer-reviewed.

What they did

The team, based in Poland, first measured six metals in worms at intervals over 16 days of adult life. They then took old worms, six days after they had stopped laying eggs, and moved them to plates with different amounts of zinc chloride, from very little to a lot. Starting this late meant that any effect would be on aging itself, not on growth or reproduction.

They followed how long the worms lived and how well they moved, measured thousands of proteins at once (proteomics), tested how much new protein the worms were making, and challenged them with heat and a toxic chemical. Finally they used two worm strains that carry disease-like proteins in their muscles: one with a long repeat of the amino acid glutamine, like the protein behind Huntington's disease, and one with human amyloid-beta, which clumps in Alzheimer's disease.

What they found

• Zinc drains away with age. After a small rise early in adulthood, the worms' zinc fell steadily, to about 90% below its starting level by day 13. No other metal measured dropped like this.
• A low dose helped, a high dose killed. At the best dose (10 micromolar), median remaining life went from 9 to 12 days, and the worms moved more. At the two highest doses, half of the worms were dead within a day. A chemical that soaks up zinc cancelled the gain in movement, so the effect needed zinc itself.
• More ribosome parts, more protein. After one day on zinc, 236 proteins went up and 249 went down. The biggest group going up was ribosome building blocks. By day three, the worms were making about 36% more new protein. Yet they did not make more ribosomal RNA, the other main ingredient of ribosomes, which suggests zinc helped existing ribosomes rather than building new ones.
• Better defences. An antioxidant enzyme whose activity fell with age returned to young levels, and treated worms survived longer under heat and under a chemical that causes oxidative damage.
• Less clumping. In the glutamine-repeat worms, zinc slowed the build-up of clumps (about 52 versus 72 per worm after three days) and raised median survival from 5 to 7 days. Worms with amyloid-beta became paralysed more slowly.

What to keep in mind

• Worms are not people. These are small animals on a lab dish, and a few extra days in a worm's life cannot be translated into human years. The study did not test zinc in mammals or people.
• The dose window was narrow. The same metal was toxic at higher doses. The authors also note that earlier worm studies found that a lot of zinc shortened life and removing zinc lengthened it; they suggest the effect depends on how much zinc the animal had to begin with.
• Short-lived changes. Most of the protein changes had faded after three days of treatment.
• Some steps are still guesses. The team saw a rise in a gene used for autophagy, the cell's recycling system, but notes that this alone does not show that recycling actually increased. How zinc protects the ribosome is a proposed explanation, not yet proven.
• Not a reason to take supplements. Too much zinc causes problems in people too, and this study gives no human dose.

Why it matters

Many aging studies slow ribosomes down to extend life. This one points to something different: that in old animals the problem may be not how much protein is made but how well the machinery works, and that a common trace metal lost with age may be part of it. The authors see late-life zinc as a lead worth testing against protein-clumping diseases. Studies in mammals, and then careful trials in people, would be needed before anyone can say whether it matters for human aging.