Someone on this forum recently asked about placating the worries of loved-one, surrounding the risk of dying in a marathon. First the headline... if my understanding is correct, my first marathon next week will, on average, on one hand cost me 2 hours off the length of my life... but on the other... it has already added at least 15 days to my life... and this amount will continue to grow. But that is not, of course, the full story.

On average, everyone running a marathon has a 7 in 1,000,000 chance of dying. That would cut about 30 years off the lifespan that I can expect. So, if 1 million people just like me ran a marathon, then on average, 7 would die, but 999,993 would live on a further 30 years. Those few sudden deaths would, on average, cost those million people about 2 hours of their lives (little comfort if you are one of the 7.... but hey, you know what I mean)

BUT... every single day you spend at 5kg overweight, you lose 30 minutes off your life. Tick tock, tick tock... every day. As it happens, I have lost exactly 5kg during training... and have been at this lower weight for at least a month. So that's 15 days added. And I understand that if you also run 30 minutes a day, the other health benefits add 30 minutes per day to your life. So that's a bit more in the bank too.

This comes from a really interesting programme 'Tails You Win:the science of chance' last night on bbc4. One concept that was discussed was that of a unit of measurement of the chance of death.... the micromort (=1 in a million chance of death).

Some stats were flashed up, with 'running a marathon' = 7 micromorts. My daughter was not impressed, with my marathon around the corner.

This sounded a bit risky to me... especially as it is a global figure. Undoubtedly it's the average risk for the whole starting line up, which will include lots of young fit people.. Those of us in our late forties, undertaking our first marathons, and still carrying a bit of a belly around the course... presumably we have more than our fair share of micromorts.

But to put into context, there are the big health benefits mentioned at the top of this post. Another context is to think of the other risks we accept.

If you live just 20 miles from the event, and travel there and back by motorbike, your journey will equal 7 micromorts

Cars are a lot safer, but still 1750 miles = 7 micromorts

walking 17 miles = 1 micromort.

Skydiving = 7 micromorts.

But an interesting point... the tv presenter is 59yrs old. He has 7000 micromorts chance of dying of any cause in the next 12 months. So adding 7 more isn't really a lot.

I think this is useful in putting the risks into perspective.

You can read more yourself on a related website, which seems to be written by the presenter of the programme... Prof Spiegelhalter www.understandinguncertainty.org/