It is really very difficult to force people to live more healthily than they want. The federal government has mandated safer cars, but research has consistently shown that such mandates lead people to drive more recklessly. (See also this study from the Review of Economics and Statistics.) The number of accidents actually increases after safety features such as seat belts are mandated for cars. True, the occupants of a car are more likely to survive an individual accident, but generally the number of accidents increases by enough to offset the safety benefits. In addition, more pedestrians and bicyclists are struck by cars.

This finding also applies to NASCAR drivers. And bicyclists are more likely to get hit by cars when they wear safety helmets.

This phenomenon is so pervasive that economists have even given it a name: the Peltzman effect, after the University of Chicago economist who first discovered it in 1975.

And it hasn’t been noticed just for automobile safety and food. The effect has shown up in childproof medicine bottles, where the childproof tops result in parents’ storing medicine in places that children find easier to reach, thus offsetting the benefits of the tops.

Possibly most relevant for Mayor Bloomberg, Peltzman recently noticed the result again in research showing that even great medical breakthroughs have little long-run effect on mortality rates. One of the most significant medical breakthroughs in human history was the development of antibiotics and other anti-infective drugs. Today, people no longer face a high risk of dying from past scourges like scarlet fever or tuberculosis. But these health benefits were offset when people began taking more risks, which led to more accidents, or when they changed their diet and exercise habits.