Regular exercise may help keep teenagers’ blood pressure in check, regardless of their body weight, a new study suggests.

Researchers found that among nearly 1,300 Canadian teenagers they followed for five years, declining exercise levels over time were linked to small increases in blood pressure.

Gains in body fat were also linked to blood pressure increases, but excess weight did not fully account for the relationship between exercise and blood pressure changes -especially in girls.

The implication, the researchers report in the American Journal of Epidemiology, is that both weight and exercise habits independently affect teenagers’ blood pressure.

And that means that getting teens off the couch might help keep their blood pressure under better control, write Katerina Maximova and colleagues of McGill University in Montreal.

The findings are based on 1,293 boys and girls who were 12 to 13 years old at the start of the study. The teens reported on their typical physical activity levels and had their body fat and blood pressure measured at the outset, and then periodically over five years.

For each exercise assessment, the teenagers reported the number of times in the past week they had engaged in moderate to vigorous activities - like biking, walking or jogging - for at least 5 minutes.

Overall, the researchers found, the teens’ blood pressure inched upward for each session of exercise they lost over time. The increase amounted to less than one point in systolic blood pressure - the top number in a blood pressure reading - but the findings do suggest that sedentary lifestyles directly affect teenagers’ blood pressure, according to Maximova’s team.

And that, they write, could have “important public health implications.”

High blood pressure and other heart disease risk factors like type 2 diabetes and High cholesterol were once uncommon, or unheard of, in children and teenagers. But rates of these conditions in teenagers have risen since the 1990s, in tandem with escalating obesity rates.

A study of Canadian teenagers published last month found that between 2002 and 2008, the percentage with at least one heart disease risk factor - such as high blood pressure or High cholesterol - rose from 17 percent to 21 percent.

Those researchers also noted that more than half of Canadian children between the ages of 5 and 17 are not getting enough exercise.

And while young people may not see immediate health effects, studies show that teens who are overweight, inactive and carrying heart disease risk factors tend to become adults with those same problems.

The American Heart Association recommends that all children ages 3 and older have their blood pressure checked yearly. Diet changes and exercise are usually the first-line treatment for high blood pressure in teenagers, though some may also need medication.

When it comes to exercise, experts generally recommend that kids strive for 30 minutes of moderate activity, like brisk walking, on most days of the week, as well as 20 minutes of vigorous exercise, like running or bicycling, at least three days per week.

SOURCE: American Journal of Epidemiology, November 1, 2009.