Life Wellbeing Book excerpt: Norman Swan explains how our lives are measured by the ‘kidney clock’
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Book excerpt: Norman Swan explains how our lives are measured by the ‘kidney clock’

Our kidneys may reflect our real age, writes Dr Norman Swan. Photo: Getty/TND
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How old are you really?

It’s all very well saying you’re 39 or 69 but all of us know people in their 30s who look decrepit and people in their 70s who look young, are so bursting with wellbeing they put the rest of us to shame and can climb Kilimanjaro before breakfast.

It makes a mockery of chronological age.

Our biological age – how old you are on the inside – can, to a significant extent, defy time. But how do you know how old you are on the inside?

The kidney clock

People tend not to think about their kidneys unless something goes wrong with them and research is suggesting that’s a mistake. In fact, our kidneys may reflect our real age. It’s also known that by the time the standard test of kidney function – the creatinine level in your blood – is registering as abnormal, you’ve already lost 30–40 per cent of your kidney function. At that point – and it’s probably a tipping point – your kidney damage starts to multiply your risk of heart disease and stroke. If someone has reduced kidney function, they’re probably a lot older biologically than their last birthday would indicate.

It looks as though the activity levels of certain genes in the kidneys correlate with our biological age better than the time we’ve had in our mortal coils. Researchers are finding that it has a lot to do with how energy is made in cells and the tissue- damaging oxygen free radicals produced as a by-product. This ties in with the inflammation story because that, too, has a link to free radicals. It’s not that our kidneys control how we age, it’s more that they may be clocks – windows through which we can see what’s truly happening inside ourselves. How these energy pathway genes work in muscle may also be a good indicator of ageing.

There’s also a possibility that a simple blood test can give advanced warning that our kidneys might be going over the hill. The test is called cystatin C and is showing promise although there’s lots of work to be done to see if it’s reliable enough to be widely used.

Preserving kidneys

The common things that damage kidneys are: your mother’s health when she was pregnant with you (if it was poor or she smoked, then you could have been born with small kidneys with less reserve for ageing); smoking; high blood pressure; and possibly inflammation from being too fat, having diabetes or not getting enough exercise.

What you can do is: keep your blood pressure low by losing weight; exercising; limiting salt and alcohol intake or taking medications if necessary; not smoking; possibly avoiding advanced glycation end products (AGEs, see Brown Isn’t Such a Good Colour); and adopting a Mediterranean style diet.

This is an edited extract from So you think you know what’s good for you? by Dr Norman Swan, published by Hachette Australia. RRP $39.99.