One way we talk about saving money in health care is prevention: If we prevent a teenager from taking up smoking, for example, we might prevent the costly conditions, the lung cancers and cardiac conditions associated with tobacco use.

Turns out, like many things in health care, it's not quite so simple. New research published in the journal Health Affairs modeled what would happen if lots and lots of people stopped smoking, right this very minute. They find that life expectancy would increase by 3.7 years for smokers, while health-care costs, tethered to that extended longevity, would rise by $1,700.

The study uses data from TRICARE, the health-insurance program that covers 9.6 million active duty or retired military members and their families. Tobacco use cost the program about $560 million in extra spending in 2006, making it one area where the Department of Defense could potentially cut out some costs.

The researchers modeled what would change about TRICARE's health-care costs if its 612,332 smokers quit right away. They used demographic data, what we know about life expectancy and health-care costs for smokers and non-smokers, to see how that would change the program's spending.

Life expectancy went up by 3.7 years, with the changes most significant among the youngest smokers who expected to kick the habit. 

A full reduction in smoking would also cut into the health-care costs associated with tobacco use. The researchers estimate that, on average, this would work out to $5,600 in savings. 

Those, however, would be more than offset by the increased cost of extended longevity, with that prolonged lifespan expected to come at the cost of $7,300. The researchers contend the $1,700 is a pretty tiny number in the grand scheme of health-care costs, especially given the 3.7-year increase in life expectancy. To put it into context, that works out to about one-tenth of the cost of an average hospital stay in the United States.