Poor levels of physical activity coupled with an unhealthy diet are raising the risk of today's teens growing up to have serious health complications, says a new study.

The data for the study came from over 4,200 participants between 12 and 19 years of age who were enrolled in the National Health and Nutrition Surveys. Researchers found that about 80 percent of this sample group, representing more than 33 million U.S. kids, had a poor diet.

The study also found that less than 50 percent of all girls and just about 67 percent of boys got the recommended amount of exercises.

And, a third of all teenagers in the country had poor or intermediate cholesterol levels. The study, researchers said, provides a snapshot of the way teens in the U.S. are living now.

"The far less-than-optimal physical activity levels and dietary intake of current U.S. teenagers, is translating into obesity and overweight that, in turn, is likely influencing worsening rates of high blood pressure, high cholesterol and blood glucose at these young ages," said Christina M. Shay, from the University of Oklahoma, and lead author of the study.

Centers for Disease Control and Prevention (CDC), says that 17 percent of all children in the U.S. or 12.5 million children and teens in the country are affected by obesity. Obesity can be a risk factor for many health complications that may last a lifetime.

"The status of heart health during childhood has been shown to be a strong predictor of heart health in adulthood. Members of the medical and scientific community, parents, teachers and legislators all need to focus their efforts on the prevention and improvement of all aspects of cardiovascular health - particularly optimal physical activity levels and diet-as early in life as possible, beginning at birth," Shay said.

The study is published in the journal Circulation.