WASHINGTON (AP) -- Tobacco companies deliberately changed the menthol levels in cigarettes depending upon whom they were marketing them to -- lower levels for young smokers who preferred the milder brands and higher levels to "lock in lifelong adult smokers," researchers at the Harvard School of Public Health concluded.

The researchers reviewed industry documents dating back decades on product development and on strategic plans for menthol products.

They said that the tobacco companies researched how controlling menthol levels could increase sales among specific groups. Milder brands with lower menthol levels appealed to younger smokers. The milder products were then marketed to young consumers.

One document from R.J. Reynolds noted that all three major menthol brands "built their franchise with YAS (younger adult smokers) ... using a low-menthol product strategy. However, as smokers acclimate to menthol, their demand for menthol increases over time."

In 1987, R.J. Reynolds marketed low-level menthol varieties to persuade consumers to switch from regular brands and to recruit new, young smokers, noting: "First-time smoker reaction is generally negative. ... Initial negatives can be alleviated with a low level of menthol."

Philip-Morris USA used a two-prong strategy to increase Marlboro's share in the menthol market by targeting young adults and older smokers, the researchers concluded. Marlboro Milds were introduced nationally in 2000 and became popular among young smokers. The entry of that product coincided with an increase in the menthol level of the regular Marlboro Menthol brand intended for older smokers. The milds were responsible for almost 80 percent of the company's menthol-category growth that year.

"For decades, the tobacco industry has carefully manipulated menthol content not only to lure youth but also to lock in lifelong adult customers," said Howard Koh, a co-author of the paper.

William Phelps, a spokesman for Philip Morris USA, the nation's largest tobacco company, said the study's conclusions were not supported by the facts cited. He said the study includes excerpts from several marketing documents. None talked about targeting youth or adolescents.

"At our company, our marketing goal is to find way to effectively and responsibly connect brands with adults who smoke," Phelps said. "Those brands are designed to meet the diverse preferences of adults who smoke. What we disagree with are the authors' conclusion that menthol levels were manipulated to gain market share among adolescents."

R.J. Reynolds said it agrees that individuals select their preferred menthol levels to create desired sensory effects while smoking, and that there is a broad range of menthol levels among popular brands. But the company said all of its products are made for and marketed to adults.

"The bottom line is minors should never use tobacco products and adults who do not use or have quit using tobacco products should not start. That is a guiding principle of the company," the company said in a statement. "It would appear this report is simply an effort to push support for federal regulation of the tobacco industry, not a scientific review of the menthol category."

Gregory Connolly, one of the report's co-authors, said the tobacco industry was careful not to talk about adolescents in the documents he reviewed, mostly from the '80s and '90s.

"They talk about young smokers. For me, that's just a euphemism for going after adolescent, first-time smokers," Connolly said.

Congress is considering legislation to give the Food and Drug Administration the power to regulate tobacco. And while the bill would ban fruit and candy flavorings, it would allow the continued sale of menthol-flavored brands. That has led to sharp criticism from some smoking control advocates, who argue that menthol lures some people to try cigarettes and helps keep others from trying to quit. The advocates are pressing for an amendment to ban menthol, an additive that gives cigarettes a mint flavor.

But Phelps said that would be a mistake. "We don't believe it's right to ban a particular ingredient because some people prefer the flavor that ingredient provides," he argued.

Philip Morris is the only one of the major tobacco companies supporting FDA regulation, and its backing for the legislation is considered important in gaining passage.

Phelps said the bill, as currently written, would allow the FDA to ban menthol if the agency determines through scientific investigation that the flavoring increases the harm associated with smoking.

Brands marketed as menthol cigarettes make up about 27 percent of the U.S. cigarette market. While overall cigarette sales have declined, sales of menthol cigarettes have been stable in recent years.

Data analyzed in the study indicates that significantly more adolescents and young adults smoke menthol cigarettes than older people. It also emphasizes that black smokers in the United States smoke menthol cigarettes, 70 percent as compared with about 30 percent of white smokers.

"We know that menthol cigarettes are disproportionately marketed to the African-American community and that starting at a young age, menthol cigarettes are the product of choice for black smokers," Dr. Cheryl G. Healton, president and chief executive officer of the American Legacy Foundation, which helped fund the study. "This research confirms that the industry is intentionally manipulating these products in order to get new smokers hooked."

The foundation describes its mission as building a world where young people reject tobacco and anyone can quit. The National Cancer Institute also funded the research.

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