J shaped risk curves versus linear risk curves: drinking versus smoking

Too often, when I ask patients if they smoke cigarettes, I hear, “Oh, only 2 or 3 a day”, as if, not a problem, no big deal, like saying, “when I play Russian roulette, there’s only one bullet in the gun”.

There was a nice little article in JAMA recently explain why sometimes even a little bit matters.


If you plot relative risk of mortality on the y-axis, and number of cigarettes/day on the x-axis, you see a simple linear association. Each cigarette smoked increases mortality risk. So with  1-4 cigarettes/day, the relative risk is 1.5, 5-9 cigarettes 2.0, 20-24, 3.0.

In contrast, alcohol, measured in drinks/day, has a j shaped curve. “Consumption of up to 2 drinks/day in women and 4 drinks/day in men was associated with lower mortality than zero consumption, with about one-half drink per day associated with the lowest mortality risk.”

So, better not to smoke.

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