Jeremy Laurance: Markers of physical health are determined at birth

The worst outcome of today's report from the Medical Research Council would be a sudden increase in bone-crunching handshakes delivered by men – or women – anxious to hold the Grim Reaper at bay.

That would not only be sadistically anti-social, it would be to misunderstand the nature of the finding.

Grip strength, and the other measures of physical capability, are markers of our state of health. They are determined, possibly as early as the womb, and are subsequently influenced by nutrition, physical fitness, smoking and other lifestyle factors.

Reversing a lifetime of louche living is not as simple as crushing another person's hand. But a weak grip could become a useful signal of when it is time to get off the sofa and on to the bike.

More work is needed to establish a "normal" grip strength for each sex and age group, and by how much a weaker grip, measured in kilograms, reduces life expectancy. The same is true of walking speed and the ability to rise out of a chair quickly or stand on one leg. Simple measures require simple cut-off points, which would enable us to say this is the stage at which intervention is required.

Until then, anyone who wants to know how long they will live should start by looking at their parents. The genes you are born with have the greatest influence on your longevity, and if your parents are long-lived then there is a good chance you will be too.

The die is cast at the moment of conception – everything that happens afterwards is tinkering around the edges.