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Consumption of soda and other sugary drinks fell by more than a fifth in low-income neighborhoods of Berkeley after the California city became the first in the U.S. to introduce a special tax last year, according to a study published Tuesday.

The peer-reviewed research is the first to measure the impact of the penny-per-ounce tax. It found that consumption declined 21 percent and many residents switched to water after the tax went into effect in March 2015, according to the study published online in the American Journal of Public Health.

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The study states that the results “suggest’’ that the tax lowered consumption but acknowledged other factors also could have been at play, including increased awareness about the health impact of sugary drinks.

The American Beverage Association, an industry group, said the Berkeley study has flaws and there is no indication the tax has had a measurable impact on public health. Street surveys relying on people’s recollections are “inherently unreliable,” said Brad Williams, an economist who does consulting work for the association.

Click for more from The Wall Street Journal.