By Dr. Brian McDonough, Medical Editor

PHILADELPHIA (CBS) - According to a Swedish study of 700,000 people, your fitness level as a teen may have future heart health implications: the exercise you do as an adolescent may actually reduce heart attack risk in the future.

For every 15% increase in aerobic activity these men engaged in as teens, there was a corresponding 18% decrease in their risk of heart attack 30 years later.

There is another interesting point in the study - no matter how much exercise was measured, obese and overweight men still had a higher risk of heart attack than lean and normal weight men.

The bottom line: physical fitness cannot alone compensate for the cardiovascular risk associated with obesity.