The risks of bad behaviors are well known but not necessarily well understood. Most people are aware that binging on red meat, cigarettes and whiskey on a regular basis isn’t good for us -- but how to make sense of the severity of the risk? When a study reports that adults who ate an extra portion of red meat had a 13% greater chance of dying over the course of a study that spanned more than 20 years, what does that really mean? And what is a sensible person to do about it?
Writing in the journal BMJ (subscription required) on Monday, University of Cambridge biostatistician and risk communication expert David Spiegelhalter (who blogs about uncertainty here) suggested that the typical response is likely to be a shrug -- and with good reason. “People tend to dismiss effects that are perceived to lie in the distant future,” he wrote, going on to quote author (and legendary drinker) Kingsley Amis’ observation that “no pleasure is worth giving up for the sake of two more years in a geriatrichome.”
But a pleasure might be worth giving up, Spiegelhalter suggested, if people did it for the sake of the time they stood to lose every single day. By expressing a lost year of life in the far smaller, but more fathomable, units of microlives per day -- defined as chunks of 30 minutes, or one-millionth of the average person’s life after age 35 -- the risks might become keenly comprehensible.
For example, Spiegelhalter wrote, “A lifelong habit of eating burgers for lunch is, when averaged over the lifetimes of many people, associated with a loss of half an hour a day in life expectancy. Which is, unless you are a quite a slow eater, longer than it takes to eat the burger.”
Referencing an assortment of epidemiological studies, Spiegelhalter calculated that, “averaged over a lifetime habit, a microlife can be ‘lost’ from smoking two cigarettes, being 5 kg [about 10 pounds] overweight, having the second and third alcoholic drink of the day, watching two hours of television, or eating a burger.”
Simply being a man (versus being a woman) was associated with a loss of four microlives per day. People living in 2010 versus those living in 1910 gained 15 microlives per day. Men living in 2010 versus living in 1980 added eight microlives per day; women, five.
In promoting the article, which appeared in a special Christmas issue of BMJ, the journal seemed to suggest that all those potential microlives lost might be a particular concern for revelers over the holidays. "It may be the season to eat, drink and be merry, but each day of over-indulging can take several hours off your life,” the journal ominously warned in a news release.
But before you panic, partygoers: Spiegelhalter’s argument doesn’t have much to do with holiday noshing per se -- the paper noted explicitly that the microlife risks do not apply to single exposures (i.e., that blowout office party) and don’t take into account differences between individuals. Drinking a little too much eggnog while waiting for St. Nick probably isn’t going to shift your time of death up by half an hour. On average, however, when people drink too much eggnog every day for 30 years, it’s problematic.
Perhaps it’s better to think of the holiday season as a good time to be reminded of the cumulative effects of habitual overindulgence, and a chance to make things right in 2013. In addition to the scary statistics about microlives lost, the BMJ paper also noted behaviors that “gain” microlives, including eating fruits and vegetables, exercising, taking statins as needed and drinking coffee.
New Year’s resolutions, anyone?