The city of Cambridge has decreased the target fluoride concentration in Cambridge drinking water by 30 percent, in accordance with new federal guidance.

This past April, the U.S. Department of Health and Human Services lowered its recommended level of fluoride in drinking water for the first time in half a century.

The new recommendation is for a single-target concentration of 0.7 milligrams of fluoride per liter of water. It updates and replaces the previous recommended range — 0.7 to 1.2 milligrams per liter — issued in 1962.

This decision was largely based on the fact that people living in the U.S. have access to many more sources of fluoride — such as toothpaste, mouth rinses, and processed foods — than they did in the past.

The result has been a national increase in dental fluorosis since the 1980s, a condition that causes permanent white stains in the tooth enamel that range from barely noticeable to, in severe form, teeth becoming rough and pitted. More than 90 percent of dental fluorisis in the U.S. is the very mild or mild form, according to the federal government.

The new federally recommended level of 0.7 milligrams of fluoride per liter of water is intended to maintain the protective benefits of water fluoridation while reducing occurrence of dental fluorosis.

The Cambridge Water Department decreased the target fluoride concentration in the city’s drinking water from 1 milligram of fluoride per liter of water to the recommended 0.7 milligrams of fluoride per liter of water on Sept. 16. The level of naturally occurring fluoride in the city’s water sources is extremely low.

“Adjusting the fluoridation concentration in the city’s water supply was a common sense decision so that children and adults are receiving an optimal level of protection,” said Claude Jacob, the city’s chief public health officer and director of the Cambridge Public Health Department, which recommended the change to the Cambridge city manager.

This past February, the Health Department hosted a community forum intended to address questions related to the safety and importance of community water fluoridation. The forum included a panel discussion and an opportunity for public comments and questions.

Following the panel, the Health Department conducted a review of academic literature on community water fluoridation and the pending federal recommendation. Jacob noted that the Health Department was prepared to make the recommendation to lower the target fluoride concentration independent of a formal change in federal policy.

While community water fluoridation has its detractors, it has led to dramatic declines in both the prevalence and severity of tooth decay in the U.S. since the 1960s.

“Fluoridation of the city’s water supply has brought significant public health benefits to the community by reducing tooth decay and the associated health effects from the bacteria responsible for this damage,” said Jacob.