The world’s oldest man, Yasutaro Koide recently died at the age of 112. Commentators as usual, focused on his reported “secret to longevity”: not smoking, drinking or overdoing it. No surprises there. But speculation on the basis of one individual is not necessarily the most helpful way of addressing this human quest for the Philosopher’s Stone.
The “very old” do spark our interest – but is our search for a secret to longevity actually misguided? Wouldn’t you rather live healthier than live longer in poor health? Surely, what we really want to know is how do we live well in old age.
Clearly as scientists we try to illuminate these questions using populations of people not just odd individuals. Many previous attempts have approached this question by looking for differences between young and old people, but this approach is often biased by the many social and cultural developments that happen between generations, including diet changes. Time itself should not be the focus – at least, in part, because time is one thing we are unlikely to be able to stop.
The real question behind our interest in people who survive into old age is how some manage to stay robust and fit while others become debilitated and dependent. To this end, recent scientific interest has turned to investigating the predictors of frailty within populations of roughly the same age. Frailty is a measure of how physically and mentally healthy an individual is. Studies show frailer older adults have an increased levels of low grade inflammation – so-called “inflammaging”.
New research published in Genome Medicine by Matt Jackson, from our group at King’s College London, investigated this question in an unlikely place – poo. Recent evidence indicates that our immune and inflammatory systems are trained and educated in our gut, through key interactions with gut bacteria. So we asked if changes in our gut bacteria could be part of the process of inflammation driving frailty.
Our recent work found that the frailer an individual, the lower the diversity of gut bacteria they have. We looked at stool samples from more than 700 healthy British twins and found that a group of bacteria belonging to the species with a tricky and slightly unpleasant name, Faecalibacterium prausnitzii, were found in higher amounts in the healthier twins. This is a particularly interesting microbe as it has been linked with good health in many other diseases such as inflammatory bowel disease and is believed to reduce inflammation of the gut. Could this bug help protect against frailty?
There were other microbes seen in increased amounts within the frailer twins. One was Eubacterium dolichum, which has been seen to increase in unhealthy Western diets. We found the same picture when comparing frailer, more elderly, individuals from the ELDERMET study, by the University of Cork. This suggests that dietary changes might be an easy way to encourage healthy ageing.
Our study does not yet clarify whether the changes to the gut bacteria are a cause of poor ageing itself or are just a consequence of frailty – longitudinal studies that follow people over several years will be needed to sort this out. But these results are exciting for researchers in the ageing field and suggest that if you want to age well you should perhaps do fewer crosswords and spend more time looking after your microbial garden, for example by eating plenty of plant fibre, for example in a Mediterranean-type diet.