Dr. Lynn Silver Chalfin, Sonoma County's health officer for about a year and a half, announced her resignation this week in e-mails to co-workers and health care colleagues.

Silver Chalfin, 55, said Friday she was taking a public health job in the Bay Area but was not at liberty to disclose the position.

"I love the county. It's an amazing place," she said, adding that she hopes to collaborate with Sonoma County on health issues in the future.

Silver Chalfin's last day in the job that pays $202,555 a year will be Dec. 5.

Silver Chalfin said her departure has nothing to do with her strong advocacy for a controversial plan to put fluoride in most of the county's drinking water.

"I'm definitely not leaving because of fluoridation," she said, calling it "an absolutely correct and important public health policy."

Silver Chalfin, who previously served as assistant health commissioner in New York City, started work for the county part time in April 2012 and became the full-time health officer about four months later.

In New York, she pushed for a ban on artery-hardening trans fats in food establishments — the first such initiative in the nation — and a law requiring calorie labeling at fast-food restaurants.

Public health has been her life's work, including 15 years as a professor of public health in Brazil.

"She's highly skilled, has an amazing background," county spokesman Peter Rumble said. "It's a loss in the sense those skills aren't going to be here."

Silver Chalfin said her accomplishments include obtaining a $3.5 million community transformation grant that funded a variety of programs, including access to healthy foods, boosting physical activity and helping hospitals promote breast-feeding.

Other steps include a school-based dental health program starting this month, an order expanding flu vaccination for health care workers and educational campaigns next year on the health impacts of sugary drinks and nicotine addiction.

Silver Chalfin said she also worked on an "end of life initiative" aimed at encouraging people and their health care providers to discuss what treatment they want in the face of terminal disease.

Naomi Fuchs, CEO of Santa Rosa Community Health Centers, complimented Silver Chalfin's efforts.

"We'll miss her," Fuchs said. "She contributed a lot in her tenure, even if it was brief."

Supervisor Shirlee Zane credited Silver Chalfin with hard work on chronic disease, childhood obesity and dental health.

Fluoridation was the "part that a lot of people paid attention to," prompting "adamant criticism," Zane said.

In an assessment of the plan released in February, Silver Chalfin wrote that "it is more important to protect people's health than to protect some people's concern for their freedom to use unfluoridated water."

Some supervisors expressed concern over the anticipated $8.5 million cost of the fluoridation project, which would affect 350,000 residents served by the Sonoma County Water Agency in Windsor, Santa Rosa, Rohnert Park, Cotati, Petaluma, Sonoma, Forestville and the Valley of the Moon.

Brenda Adelman of Guerneville, an activist on Russian River water issues, said the county should drop the plan, calling fluoride "clearly a toxic substance" that poses various health concerns.

In discussions of the plan, Silver Chalfin did not provide "valid evidence as to its value," Adelman said.

The supervisors were scheduled to resume consideration of the fluoridation proposal in March, but Zane said that might be pushed back due to Silver Chalfin's departure.