It was late 2024, and I was sitting in a room above Birmingham’s Queen Elizabeth Hospital receiving a test called IMM-AGE which would estimate the age of my immune system. I was taking the test for the second time in a matter of months as part of my reporting for The Age Code, my book investigating the link between what we eat and how well we age.
The IMM-AGE algorithm was assessing the various populations of immune cells in my blood, and characterising them based on 12 different metrics, for example, the numbers of new white blood cells or T cells you’re generating, or the balance of pro-inflammatory immune cells to inflammation resolving cells.
Ageing scientists are interested in this for several reasons. Signs of accelerated immune ageing in a relatively young person could point to an increased vulnerability to autoimmune conditions such as rheumatoid arthritis. In later life, a person’s immune age says a lot about their ability to fight off infections, and their susceptibility to serious diseases like cancer, heart disease and Alzheimer’s. Some researchers have found it to be a better predictor of how long someone is likely to live than standard measures such as cholesterol.
“Immune ageing and inflammation play a very important role in frailty,” says Niharika Duggal, an assistant professor at the University of Birmingham’s Department of Inflammation and Ageing, whose research lab was carrying out the test. “For instance, the more of these inflammatory proteins you’re producing called cytokines, they can drive loss of muscle.”
In future, it’s possible that IMM-AGE could be incorporated in health check-ups. For now, it remains a research tool, but one which is already revealing new secrets about the kinds of activities which can speed up and slow down immune ageing. And as I cover in my book, one of the biggest things which influences immune health is our diet.
Less fat, more T cells
I was returning to Birmingham to find out whether a two-month dietary experiment, aimed at reducing my calorie intake and boosting the amounts of nutrients in my diet through excluding all highly processed foods and replacing them with whole foods, had made a difference to my immune health.
After my two month dietary experiment, my immune age had reduced by two years
It turned out that it had. IMM-AGE revealed that a particular population of inflammatory immune cells had almost halved, while the so-called regulatory T cells which dampen inflammation and tune the immune system had doubled. Even in this short time, my immune age had reduced by two years. This matched with Duggal’s findings from various studies.
She explained that many of us experience premature immune ageing because of the steady acquisition of visceral or internal fat over many years, typically exacerbated by a high proportion of ultra-processed foods in our diet. This fat begins to clog up a small gland called the thymus, which is responsible for ensuring that we have a fresh supply of new T cells. As the thymus becomes ever more filled with fat, it shrinks, and the T cell pool diminishes, increasing our risk of disease.
Another key reason was likely because I had been consuming less saturated fat and more dietary fibre and omega-3 rich foods like oily fish, a balance which Duggal has found to be critical for immune health. This is linked to how these foods are metabolised within the gut. Saturated fats are broken down into inflammatory substances called ceramides, while fibre and omega-3s lead to the production of anti-inflammatory chemicals known as short-chain fatty acids and resolvins.
Duggal says that a heavy imbalance of ceramides to short-chain fatty acids and resolvins can lead to a condition known as leaky gut, where microbes seep into the circulation where they chronically aggravate immune cells. “It’s how the immune system ages,” she says. “We have a cohort of people we’re following who are in their sixties who all seem to be protected from some features of immune ageing. Some of the key features are that their fibre intake is very good, and their saturated fat intake is moderate.”
The boost of positive stress
But there’s also another key theory shared by ageing scientists, namely that a certain amount of positive stress — known as hormesis — can be highly beneficial for the immune system.
Exercise serves as one form of positive stress, and some of the healthy immune agers who Duggal is studying are keen cyclists. But diet can be another. Researchers have long been intrigued by findings that people who consume a higher proportion of plant chemicals known as polyphenols in their diet seem to stay cognitively sharper for longer, and there are now various ideas for why.
Take pomegranates for example. Older adults who consume pomegranate supplements before open heart surgery — a traumatic operation which can often precipitate cognitive decline — were found to not only preserve their memory and cognition, but actually experienced improvements. Other researchers have found benefits to brain health from consuming passion fruit.
Rich Hartman, a researcher at Loma Linda University, told me that his working theory is that plant chemicals within some of these fruits are metabolised into substances which nudge the brain’s immune system into action. “A lot of the compounds these plants produce are irritants,” he says. “The thinking is that they’re prompting the brain to ramp up its protective mechanisms.”
While it’s possible that we may ultimately be able to develop drugs which can help reverse features of immune ageing, for now the most evidence for keeping your immune system in good health for longer lies on your plate.
