Cigarettes made in the U.S. contain more cancerous tobacco-specific nitrosamines (TSNAs) than those from other countries, a new study says.

CNN reported June 1 that the U.S. Centers for Disease Control and Prevention (CDC) compared levels of TSNAs in smokers who used U.S. brands Marlboro, Newport Light, and Camel Light to smokers of Players Lights and DuMaurier from Canada, Peter Jackson and Peter Stuyvesant brands from Australia, and Benson & Hedges and Silk Cup Purple from the U.K.

TSNA levels were three times higher in the mouths of the U.S. smokers, the study found, and twice as high in their urine samples.

Researchers said the levels of TSNA are mostly determined by how the tobacco is cured, as well as the heating process humidity, and the type of fertilizer used to grow the plant.

The study appears in the June 2010 issue of the journal Cancer Epidemiology, Biomarkers and Prevention.