A large study has found that body mass index, waist circumference and diabetes are all associated with an increased risk for liver cancer. Liver cancer is the sixth most common cancer, and its incidence has tripled since the mid-1970s in the United States.

For the study, in Cancer Research, researchers pooled data from 14 prospective studies with more than 1.5 million participants. After controlling for age, sex, alcohol use, smoking and race, they found that being overweight increased the relative risk for liver cancer by between 21 percent and 142 percent as B.M.I. increased. For each 2-inch increase in waist circumference, the risk of liver cancer increased by 8 percent, even after controlling for B.M.I. And those with Type 2 diabetes had more than double the risk of liver cancer, even among the non-obese.

There was no association of B.M.I. with cancer if the patient had hepatitis, a cause of liver cancer so strong that it overwhelms any other cause. But among those without hepatitis, the increased risk was significant.

“This study underscores that the parallel increase in obesity is part of the increase in liver cancer rates,” said the lead author, Peter T. Campbell, an epidemiologist with the American Cancer Society. “Now we have to accept the fact that obesity and Type 2 diabetes are strongly associated with liver cancer.”