Kristine Madsen, MD, is an Associate Professor in the School of Public Health at the University of California, Berkeley. She spoke with us about the impact of soda tax legislation on the health of communities.

Several cities had soda tax measures on the ballot this year that turned out to be successful. Where did these taxes pass?

Four cities passed a soda tax in 2016: three in California—San Francisco, Oakland, and Albany (a small town next to Berkeley)—along with Boulder, Colorado. In California, the legislation is similar: one cent per ounce on sugar-sweetened beverages; in Boulder, it’s two cents per ounce. Both Philadelphia and Illinois’ Cook County, which includes Chicago, also enacted beverage taxes this year, though these taxes included artificially sweetened drinks as well as sugar-sweetened beverages. [Editor's note: The Cook County sweetened beverage tax was repealed in October 2017.]

Berkeley was the first U.S. city to pass a soda tax, in 2015. What has the impact been?

Our study, which looked at the results after the tax was in place for six months, found that sugar-sweetened beverage consumption dropped by 21 percent vs. an increase of 4 percent in Oakland and San Francisco, two comparison cities that didn’t have the soda tax at that time. We looked at 3,000 adults age 18 to 90 from the three cities; and we focused on low-income neighborhoods in each city that had the highest Latino and African-American population and also the highest number of people with only a high school education. Why did we choose those neighborhoods? Because that’s where diabetes and obesity and advertising for sugar-sweetened beverages are the greatest.

Do we know if the reduction in consumption is a direct result of the tax, or could it be simply a growing awareness of the effect of sugary beverages on health?

I expect it’s both. Any major public health success we’ve had—widespread vaccination, reduced cigarette smoking, motor vehicle safety, control of communicable diseases—they’ve all relied on two things: legislation that holds people accountable or makes them pay a penalty for engaging in the unhealthy or risky behavior, and public awareness campaigns. The impact of any type of policy will be greater if paired with increased social awareness. When you put an issue to a vote, it increases public awareness. One thing to keep in mind: In 2014, San Francisco also had a soda tax on the ballot, but it lost by a small margin. This time, the city ran a campaign that more effectively communicated with the public—and it passed.

When a soda tax is imposed, can’t people simply go to another city to avoid the tax?

We asked Berkeley residents directly if they switched where they bought soda in response to the tax. Only 2 percent of the people we interviewed said they had switched cities.

What do people switch to drinking instead of sugary drinks?

The list of drinks was not exhaustive in our study. But we suspect that the switch was largely to water. With the 21 percent decrease in sugar-sweetened beverage consumption, we saw a 63 percent increase in water consumption in Berkeley versus a 19 percentincrease in the comparison communities of San Francisco and Oakland, which did not yet have soda taxes. (The overall increase in water consumption likely reflects that 2015 was the hottest summer on record in the Bay Area.) The much larger increase in Berkeley suggests that people in Berkeley replaced the sugar-sweetened beverages with water. This is the best possible outcome, from a public health perspective. It also means that those people saved money by not purchasing the now more-expensive soda.

Do we know whether a reduction in soda consumption is enough to impact obesity?

It will take a few years before we know what the health implications of soda taxes are. However, a study released this month used data from Mexico, which introduced a national soda tax in 2014, to predict long-term health outcomes. Using computer simulation, the researchers found that Mexico’s soda tax will lead to a profound decrease in obesity-related disease, like diabetes and coronary heart disease, with significant cost savings. As large cities like San Francisco, Philadelphia, and Chicago implement their beverage taxes, hopefully we will be able to make similar predictions for the health implications of taxes in the U.S.

What’s the opposition to the tax?

The industry is casting doubt on the longer-term health impact of reducing soda consumption via taxing soda. It’s put out false reports similar to what the tobacco industry did with smoking. They say there’s no evidence that added sugar causes cardiovascular disease, for example. But there are at least 37 randomized trials showing that diets high in added sugar cause disease, including higher blood sugar, higher blood lipids (like cholesterol), and higher blood pressure. Other research has shown that about half of the added sugar in the average American diet comes from soda and other sugar-sweetened beverages. So the evidence is clear—both that added sugar is bad for health, and that reducing soda consumption is a way to cut the added sugar in a person’s diet.