Traffic congestion may not only add stress...but weight and other health problems as well.Michelle Gielan has that story and more in today's health watch report.Your chances of becoming a professional athlete may depend on your birthday.A new study out of Australia suggests kids born earlier in the year are more likely to become athletes.The author of the report says being born earlier gives many children a size advantage over their classmates which translates into success on the playing field.Traffic congestion may increase a child's risk for obesity.A new study says that's because when it's not safe to play outside, kids are more likely to stay indoors and play computer games or watch television.Researchers suggest air pollution which can negatively impact asthma andAnd.. your social status may depend on the makeup of your brain.Researchers conducted brain scans of volunteers to assess their levels of social status.They found those with higher levels of dopamine -- which plays a major role in motivation and reward -- were also more like to have higher social standing.Those are some of today's top medical stories.I'm Michelle Gielan - CBS News - New York