Children and teens in the U.S have a high risk of developing high blood pressure, according to a new study conducted by researchers at the Harvard Medical School, Boston. Researchers said that the risk of high blood pressure among children increased by about 27 percent during a 13 year study period.

According to researchers, rising obesity, expanding waistlines and increase in salt consumption may be the reason behind the rise of blood pressure among children and teens.

Centers of Disease Control and Prevention (CDC), says that about 18 percent of all children and teens in the U.S are affected by obesity. According to the agency, children now are getting heavier than ever. In the past few years childhood obesity has almost tripled.

In 2012, a related study had found that even with a rise in obesity rates, there has been no sign of rising blood pressure among children in the country. High blood pressure is a serious condition that can lead to coronary heart disease, heart failure, kidney failure, stroke and many such diseases. According to National Heart Lung and Blood Institute, a person may be suffering from high blood pressure and not know about it for years because the disease usually has no signs or symptoms.

The new study found that the risk of high blood pressure grew by about 27 percent during a thirteen year period.

"High blood pressure is dangerous in part because many people don't know they have it," said Bernard Rosner, Ph.D., lead author of the study and professor of medicine at Harvard Medical School in Boston, Mass. "It's a very sneaky thing. Blood pressure has to be measured regularly to keep on top of it."

The study was based on data obtained from 3,200 children aged from 8 to 17 enrolled in the National Health and Nutrition Examination Survey (NHANES) III in 1988-1994. They compared the health records of these children with that of over 8,300 in NHANES in 1999-2008. Researchers accounted for other factors such as race, age and sodium intake.

In both the groups, over 80 percent children had salt intake of over 2,300 milligrams. But in the second group of children, few consumed salt of over 3,450 milligrams.

The study found that although boys had higher blood pressure levels and were obese, the rates for blood pressure and obesity increased drastically for girls during the study period. African-American children had 28 percent blood pressure than non-Hispanic white children. Also, children who consumed high amounts of salt had a 36 percent increase in risk of blood pressure when compared with children whose salt consumption was low.

The average sodium intake for Americans aged 2 years and older is 3,436 mg per day, according to Centers for Disease Control and Prevention. Also, salt in the diet doesn't just come from the salt-shaker at the table, but also from the processed food. A recent study also indicated that at least 75 percent of all pre-packaged foods marketed for toddlers have high level of sodium.