CAMPAIGNING in the city last week, Democratic presidential candidate Bernie Sanders criticized Mayor Kenney's sugary-drink tax proposal as "regressive," saying the burden would unfairly fall on poor people, who on average drink more sugared soda and other soft drinks.

Sanders meant it was regressive in the economic sense. But, there is evidence the tax may be "progressive" in a public health sense by lowering the rate of diabetes and obesity, which also on average afflict more poor people.

That conclusion comes from a Harvard University study conducted by Steven Gortmaker and funded by several pro-health, anti-sugar groups. It's based on the assumption that higher prices on sugary drinks will reduce consumption.

Gortmaker estimated that the 3-cents-per-ounce drink tax could prevent 2,300 cases of diabetes a year and help thousands more avoid obesity. Over the next 10 years, that could save $200 million that would otherwise be spent on medical bills.

That is not small change. And the results of the study are not surprising.

For years, public health officials have tried to wean Americans off the empty calories in sodas and snack foods that have added sugar. Anyone who has ever gone on a diet (raise your hand if you have) knows the first step to take is to cut back on sugar intake: switch Coke to Diet Coke, for example.

Health experts estimate that adult males should limit their intake of sugar intake to 150 calories a day - equal to about nine teaspoons; women are urged to consume no more than 100 calories a day, the equivalent of six teaspoons.

Do Americans follow these recommendations? Of course not. Ever since infancy, we've been trained to crave sweet food and drink.

According to the latest figures, the average adult consumes 22 teaspoons of sugar a day, equal to about 365 calories. The average child consumes 32 teaspoons a day, equal to 531 calories.

Again, these are averages. Drinking soda morning, noon and night will send your sugar consumption off the charts.

Kenney has not said a word about the public health side of his sugary-drink proposal. To him, it is a matter of applying a tax to raise the money needed to expand pre-kindergarten to nearly every 3- and 4-year-old in the city.

But the public health side benefit shouldn't be overlooked. Governments often try to encourage or discourage behavior through tax policy. Example: It's been public policy goal to encourage home ownership, so mortgage interest payments are exempt from taxes.

Example 2: It's been a public health goal to reduce cigarette smoking to reduce the incidence of lung cancer and heart disease So, cigarette taxes tend to be high, restrictions are in place against advertising, regulators actively go after merchants who sell cigarettes to minors, and we have laws that prohibit smoking in many places. As a result, the number of adults who smoke has been in decline for decades: from 33 percent in 1980 to 17 percent in 2014. And it is expected to continue to decline. That decline has resulted in untold billions in savings on treating smoking-related diseases.

A local 3-cents-per-ounce on sugary drinks won't change the world. We have a long way to go to see such a steep drop in sugar consumption. But, it is a small step in the right direction. We call that progress.