IF you want to get an idea of how fast you’re ageing, you can get a clue from looking at your own, a genetics expert has suggested.

The number on your passport isn’t the only indicator of how well you’ll stand the test of time.

Experts increasingly look towards biological age to predict someone’s risk of disease, age-related decline and how long they might live for.

Signs of ageing are of course visible to the naked eye – such as grey hair, wrinkles, increased stiffness as you move – but the process also happens in your cells, and this is what biological age refers to.

If someone has a lower biological age compared to their chronological age, suggesting they are ageing slower, they may enjoy a longer healthspan – the number of years they live while healthy, active and free of disease.

According to Dr David Sinclair, a tenured Professor in the Department of Genetics at Harvard Medical School, your nails might be able to shed some light on your biological age.

Speaking on an episode of his podcast Lifespan, he said “the rate of your nail growth is a really good indicator of how you’re ageing or not ageing”.

Dr Sinclair said this came about from a study conducted in 1979 by researchers at the Orentreich Foundation for the Advancement of Sciences.

“The linear nail growth rate is a simple, inexpensive, noninvasive technique for the measurement of ageing,” study authors wrote.

“The rate of linear nail growth decreases 50 per cent over the life spans of humans,” they added.

Scientists attached tiny measuring tapes to the fingernails of 271 people – aged between 10 and 100 and tracked their growth over years.

They also used the data of one participant who measured how much his nails grew between the ages of 32 and 36, recording how long it would take for their nails to reach a specific length.

Researchers found that weekly fingernail growth rate decreased by about 0.5 per cent per year from the age of 30. 

“Men had a more rapid [growth] rate than women until the sixth decade”, they wrote, but “by the eighth decade women had a more rapid rate than men”.

If nails grow faster and you need to cut them more often than other people your age, it could be a sign you’re ageing at a slower rate than average, the researchers suggested.

Dr Sinclair said of the findings: “We now know for sure that the rate of nail growth decreases by about 0.5 per a year and if you measure that it’s a really good indicator of how old you are biologically.”

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The genetics expert said he applies the study’s findings to his own life – though he doesn’t go to the trouble of meticulously measuring how much they’ve grown.

“I do pay attention to whether my nails are slowing down in their growth or not,” he said.

“Every time I have to cut my nails, I’m thinking, how long ago did I cut my nails?”

Nail growth depends on a steady supply of nutrients and oxygen, which are delivered through the bloodstream.

As we age, blood circulation can decrease, particularly in the extremities, which may result in slower nail growth over time.

Your fingernails may also reveal other clues about your health, aside from how fast you’re ageing – as they can be affected by hormonal changes or nutrient deficiencies.

It’s normal for nails to become thicker or break more easily as you get older.

They may also become harder, softer or more brittle during pregnancy.

But brittle nails could be a sign you’re low in iron, or it could show that you have gut health problems.

Meanwhile, yellowing could indicate you have a fungal infection – or in some cases that you might have diabetes.

The disease can cause other signs in your nails, such as puffy nail beds and thickening.

A stripe along your nail is something you definitely want to get checked out, as it could be a sign of melanoma.

And clubbing – when your nails take on rounded, bulging shape, giving the appearance of an upside-down spoon – this can be a sign of underlying health conditions that need to be treated, such as lung disease or cancer or cardiovascular disease.