The researchers analyzed 16 studies that included nearly 900,000 people from around the world and found that people with prediabetes had a 15 percent overall increased risk of cancer. People with prediabetes have blood sugar levels that are higher than normal, but not high enough to be considered full-blown diabetes.

The review also revealed significant associations between prediabetes and specific types of cancer, including stomach, colorectal, liver, pancreas, breast and endometrial cancers.

There was no link between prediabetes and lung, prostate, ovarian, kidney or bladder cancers, according to the study published Sept. 8 in the journal Diabetologia.

The study found an association but not a cause-and-effect relationship between prediabetes and certain cancers. However, the findings have important health implications, said the researchers, noting that rates of prediabetes and diabetes are rising in many developing and developed nations. For example, the rate of prediabetes among Americans aged 18 and older rose from 29 percent in 1999-2002 to 36 percent in 2007-10.

"Considering the high prevalence of prediabetes, as well as the robust and significant association between prediabetes and cancer demonstrated in our study, successful intervention in this large population could have a major public health impact," study leader Yuli Huang, a professor from the First People's Hospital of Shunde District, China, and colleagues said in a journal news release.

The study authors said the diabetes drug metformin is believed to help protect against cancer.

"Notably, metformin mediates an approximately 30 percent reduction in the lifetime risk of cancer in diabetic patients," the researchers said in the news release.

It's unknown whether metformin would reduce cancer risk in people with prediabetes, and large-scale and long-term studies are needed to determine if that's the case, the study authors said.