Cases of Cancers Linked With Obesity Increase

Story first appeared in the Wall Street Journal.

Several cancers linked to obesity and a sedentary lifestyle rose every year from 1999 through 2008, even as improved screening and a sharp decline in the number of smokers have helped push down the rate of new cancer diagnoses overall across the U.S., according to a report released Wednesday.

Rates of cancers of the kidney, pancreas, lower esophagus and uterus increased annually through 2008, the latest data available, according to the Annual Report to the Nation on the Status of Cancer. Rates of breast cancer in women at least 50 years old declined 1.3% annually from 1999 to 2005 but rose slightly between 2005 and 2008.

The data add to a growing body of evidence that obesity raises the risk of these and some other cancers. As many as one-third of common cancers in industrialized nations are linked to excess weight and lack of physical activity, according to the International Agency for Research on Cancer. Obesity rates leveled off in the U.S. a decade ago, but an estimated 68.8% of adults remain overweight or obese, according to the CDC, and cancers can take years to develop.

Obesity-related cancers include common ones, such as breast and colorectal cancer, as well as less common ones, such as pancreatic cancer. Excess weight can also decrease the chance of survival once a patient is diagnosed.

The report, published online Wednesday in the journal Cancer, is by researchers from the CDC, the North American Association of Central Cancer Registries, the National Cancer Institute, and the American Cancer Society.

The evidence of a causal link with cancer, while not yet definitive, is far clearer with excess weight and lack of physical activity than with specific foods or nutrients.

The rising rates contrast with the progress made in recent years against major killers such as lung cancer, scientists say. While tobacco use has plummeted since the 1960s, obesity rates have soared.

Overall, rates of new cancer diagnosis have been declining slightly since the mid-1990s. They fell 0.6% annually among men between 1998 and 2008. But the declines aren't uniform. Among women, rates fell 0.5% annually between 1998 and 2006 and then leveled off between 2006 and 2008.

A review of more than 7,000 studies found evidence of a link between excess weight and several cancers, according to the report. While the precise link isn't understood, fat cells can encourage the body to produce more substances such as insulin or hormones that can stimulate tumor growth, scientists say. Obese postmenopausal women may have higher levels of free estrogens and androgens, a risk factor for breast, ovarian and uterine cancers. Adenocarcinoma, in the lower esophagus, develops mostly in people who suffer from chronic stomach-acid reflux, often triggered by excess weight.

Not all of the obesity-related cancers are on the rise. Rates of colorectal cancer declined 2.6% yearly between 1999 and 2008, thanks in large part to widespread screening.  Whether the rise in obesity-related cancers will continue is unknown.