A youthful brain and immune system may be key to a long life

When it comes to living a long life, it seems not all organs are created equal. Scientists have found that having a youthful brain or immune system may be key – more so than having a slowly ageing heart or lungs.

We already knew that organs age at different rates, but it is unclear which ones have the biggest influence on lifespan, says Hamilton Se-Hwee Oh at the Icahn School of Medicine at Mount Sinai in New York.

So, Oh and his colleagues analysed the levels of nearly 3000 proteins in blood samples collected from more than 44,000 people who enrolled in the UK Biobank study when they were between 40 and 70 years old.

Using genetic data from past studies, the team was able to build a picture of where these proteins were in the body, pinpointing dozens of proteins that are especially abundant in 11 areas: the immune system, heart, brain, liver, lungs, muscles, pancreas, kidneys, gut and fat tissue. The high levels of these proteins indicate they are important in the proper functioning of these organs and body systems.

Next, the team trained machine-learning models to guess how old the participants were based on data from about half of them, creating a separate model for each of the 11 parts of the body. While these estimations generally matched the participants’ ages fairly well, some models overestimated or underestimated it, supporting the idea that organs age at different rates, says Oh.

The researchers used the trained models to predict the organ and immune system ages of the remaining half of the participants, who were followed for an average of 11 years after their blood was sampled.

Oh and his colleagues found that having one prematurely aged organ, or an aged immune system, was linked to a 1.5- to 3-fold increased risk of death during the follow-up period, with the risk rising alongside the number of aged areas.

For the most part, having organs like a heart or lungs that appeared to be substantially younger than expected wasn’t linked to a reduced risk of death during the study period. The exceptions were those with the most youthful brains or immune systems, whose risk of death was reduced by about 40 per cent – rising to 56 per cent if both of these parts of the body were particularly youthful.

“The brain and immune system coordinate a lot of other things around the body, so if those go wrong, it’s not too surprising they might have outsized effects on lifespan,” says Alan Cohen at Columbia University in New York.

But it is unlikely that protein markers perfectly reflect the ageing process, says Cohen. “We may have incomplete knowledge of what proteins really come from what organs, and the proteins from a given organ might be better represented in the blood than other organs; that could be why certain organs pop out as more important,” he says.

What’s more, the participants were mainly wealthy and of European ancestry, so further studies involving more ethnically and economically diverse people should verify the findings, says Richard Siow at King’s College London. Oh says the team is planning research that addresses this.

Even if the findings hold true, we don’t have ways to specifically reduce ageing of the brain and immune system, says Oh. However, identifying markers of brain and immune ageing could help to develop drugs that target these to boost longevity.