Smoking alters several genes associated with health problems for smokers, such as increased risk for cancer and diabetes, researchers in Sweden say. A study, published in the journal Human Molecular Genetics, identified a large number of genes that were altered in smokers but found no such effect of non-smoke tobacco. People inherit genes from their parents at birth. Later in life the genetic material can be changed by epigenetic modifications, i.e. chemical alterations of the DNA the affect the activity of the genes. Such alterations are normally caused by aging but can also result from environmental factors and lifestyle, the researchers said. "This means that the epigenetic modifications are likely not caused by substances in the tobacco, but by the hundreds of different elements that are formed when the tobacco is burnt," study leader Asa Johansson, a researcher at Uppsala University and Uppsala Clinical Research Center, said in a statement. Previous research showed smokers have an increased risk of developing diabetes and many types of cancer. Smokers also have a reduced immune defense and lower sperm quality. The results from the study also showed that genes that increase the risk for cancer and diabetes, or are important for the immune response or sperm quality, are affected by smoking, Johansson said. "Our results therefore indicate that the increased disease risk associated with smoking is partly a caused by epigenetic changes," Johansson said.