“I’m as old as my tongue and a little bit older than my teeth,” my grandmother always used to say when asked impertinently about her age.
But if she were still alive today, we might be more interested in the bugs living in or on her to work out how long she’d been around.
That’s because the biggest study to date of microbiome and age, published today in the journal mSystems, has found that the microbes on our skin, in our mouths and in our guts are good predictors of our chronological age, or the number of years we’ve been alive.
American, British and Chinese researchers analysed publicly available microbiota data from 8,959 samples in 10 different studies — 4,434 poo samples, 2,550 saliva samples and 1,975 skin samples.
What they were trying to work out was how well different microbiomes across the body could predict age through how they change as we get older, and whether such predictions would be accurate across populations, said lead author Shi Huang, a bioinformatician from the University of California San Diego.
Using machine learning, skin samples taken from either the hand or the forehead could predict a person’s age to within 3.8 years, and it didn’t matter whether the sample was taken from a man or a woman.
Saliva samples could predict your age to within 4.5 years and your poo — a measure of the microbes in your gut, and the only one of the three to show differences due to sex — was the least accurate, predicting your age to within 11.5 years.
That your skin microbiome gave the best prediction of your age didn’t surprise Emad El-Omar, director of the Microbiome Research Centre at UNSW Sydney, who wasn’t involved in the research.
“The metabolic activity of the gut microbiome is equivalent to the liver,” Professor El-Omar said, “so to a great extent there’s a lot of things that influence this, and it would be incredibly unlikely that it would fit exactly your chronological age.”
“The skin is a more accurate picture because it’s the simplest and the least complex, and the mouth is somewhat in between.”
Our microbiomes have a profound effect on our health
Aside from being inherently fascinating, why does any of this matter when you could just — gasp! — ask someone how old they are?
Well our microbiomes have a profound effect on our health, Professor El-Omar said, and without what is now accepted as this extra organ that we’re all carrying around most of our healthy normal bodily functions would not be the same.
“And everything we do in our lifestyle has an impact on [our microbiomes] either being very healthy and diverse and strong and rich, or the opposite which is basically what precipitates disease,” he said.
The bigger question that the study alludes to, is what does this kind of microbiome or “microbial age” — which is a surrogate of your chronological age — imply about your fitness and your healthy age?
“In other words, you could be 100 years old, but you’ve got a microbiome of a 50-year-old or a 20-year-old because you’re so healthy,” Professor El-Omar said.
The research team hypothesised that if they could predict human chronological age using microbial abundance profiles, they could build a reference microbiota age for healthy individuals from different age groups, Dr Huang said.
“By comparing a given individual microbiota age to the reference, we can intuitively see how far away you are from ‘normal’ at different ages,” he said.
This then provides valuable information on how healthy you are.
In the future, Professor El-Omar said he had no doubt we would see interventions that target our microbiomes to reverse the effects of ageing or to prevent the onset of age-related disease.
“The beauty of the microbiome field is it’s actually eminently manipulatable,” he said.