Coffee and beer may affect the human genome, a finding that could one day contribute to the prevention and treatment of human diseases, Israeli scientists say. Studies on a kind of yeast that shares many important genetic similarities with humans showed that caffeine shortens and alcohol lengthens telomeres, the end points of chromosomal DNA implicated in aging and cancer, scientists at Tel Aviv University reported Thursday. Telomeres, made of DNA and proteins and marking the ends of the strands of DNA in our chromosomes, are essential to ensuring the DNA strands are repaired and copied correctly. Every time a cell duplicates, the chromosomes are copied into the new cell with slightly shorter telomeres until after many duplications the telomeres become too short and the cell dies. Only fetal and cancer cells have mechanisms to avoid this fate, so they go on reproducing forever, the scientists said. While more laboratory work is needed to prove a causal relationship, not a mere correlation, between telomere length and aging or cancer, the researchers said, the suggestion human telomeres might be affected by caffeine or alcohol could some day lead to both medical treatments and dietary guidelines. "For the first time we've identified a few environmental factors that alter telomere length, and we've shown how they do it," Martin Kupiec of the university's Department of Molecular Microbiology and Biotechnology said. "What we learned may one day contribute to the prevention and treatment of human diseases."