Although the overall cancer death rate has dropped among adults and children in the United States, cancers associated with obesity and sedentary lifestyles are on the rise from 1999 to 2008, according to a new comprehensive report. 

The findings show that the rate of new cancer cases has been declining at a rate of about half a percent each year since 1999, and in adults the incident rate has dropped by 1.5 percent annually and 1.7 percent in children, according to the Annual Report to the Nation on the Status of Cancer.

Cancer death rates have declined an average of 1.7 percent annually among men and 1.3 percent among women and children from 1998 to 2008.

The report, which was a collaborative effort between the Centers for Disease Control and Prevention, the North American Association of Central Cancer Registries, the National Cancer Institute and the American Cancer Society, marks the first time these groups have highlighted the relationship between obesity and cancer.

"This report emphasizes that the growing obesity problem and decreased overall physical activity in our society compared to decades ago have a real impact on multiple diseases, including cancer," Dr. Jeffrey Meyerhardt, an author of several studies investigating the impact of exercise on survival rates for colorectal cancer patients, said in a statement released on Wednesday.

The report was based on more than 7,000 studies that have linked obesity to increased risk for colorectal and postmenopausal breast cancers, as well as cancers of the esophagus, kidney, pancreas, and uterus and lower survival rate in cancer patients who are overweight and not active.

Researchers said that for more than three decades, excess weight, inadequate physical activity, and an unhealthy diet have been second only to tobacco as preventable causes of disease and death in the United States. While tobacco use has declined by a third since the 1960s, obesity rates have doubled, significantly impacting the diseases associated with these factors.

"While we currently see declines in incidence of many cancers, if obesity continues at the current rates, I believe these improvements in incidences will reverse and increase over time," Meyerhardt said.

Obesity and insufficient physical activity have been linked to an increased risk of cardiovascular disease, hypertension, diabetes, and arthritis, and many cancers, and according to researchers from the International Agency for Research on Cancer, as many as a third of common cancers in the developed world is linked to these lifestyle factors.

Researchers said that while obesity rates leveled off about a decade ago in the U.S., they estimate that about 68.8 percent of adults remain overweight or obese.

“In the United States, 2 in 3 adults are overweight or obese and fewer than half get enough physical activity,” John Seffrin, chief executive officer of the American Cancer Society, said in a statement released. “Between children and youth, 1 in 3 is overweight or obese, and fewer than 1 in 4 high school students get recommended levels of physical activity. Obesity and physical inactivity are critical problems facing all states. For people who do not smoke, excess weight and lack of sufficient physical activity may be among the most important risk factors for cancer.”

Researchers also detected an increased incidence of the deadly skin cancer melanoma, and melanoma rates have risen by about 2.5 percent annually in women and 2.3 percent in men since 1999.

Health experts say that the rising rate shows that skin cancer is an emerging epidemic and increased efforts to get people to use sunscreen and avoid tanning beds could have a major impact on the cancer incident rate. 

While the findings do not mean that there excess weight and lack of physical activity definitely causes cancer, there is a significantly clear correlation, and researchers said that the good news is that some of the cancer risks associated with lifestyle choices can be changed.

"Many of the things that are still a problem in these statistics are modifiable," said Benz. "If you watch your diet, exercise, and manage your weight, you can not only prevent your risk of getting many lethal forms of cancer, you will also increase your chances of doing well, if you should get almost any form of cancer." Dr. Edward Benz, president of Dana-Farber Cancer in Institute in Boston, who noted while the report is encouraging, the overall rate of cancer deaths is not declining nearly enough.

The findings will be published in the May issue of the journal Cancer.