Here's a look at some of the top health news being talked about around the U.S. and the world today:

• Researchers say they're getting more and more inquiries from athletes about the rules on modifying genes to increase their endurance and muscle mass — and scientists warn they are unsure whether it is safe.

• Medical activists are joining forces and campaigning for time limits on how long medical residents can go without sleep and to increase supervision of residents. It's a move they say is necessary to increase patient safety.

• Samples of three of the top canned tuna brands in the U.S. reveals more than 50 percent had mercury levels higher than considered safe by the U.S. Environmental Protection agency.

• In one area of California, the life expectancy is 87.4 year - while only a zip code away, the life expectancy falls to 71.2 years. Reporters there investigated why in an in-depth series last month.

Tina Reed covers health and the environment for AnnArbor.com. You can reach her at tinareed@annarbor.com, call her at 734-623-2535 or find her on Twitter @TreedinAA.