Girls become less physically active once they reach teens.

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Author: Wright, Catherine

Issues at the state and community levels

PHYSICAL activity declines sharply among girls during adolescence, and black girls in particular are at risk of becoming sedentary, according to a recent study.

The study, which was published in the Sept. 5 issue of the New England Journal of Medicine, involved 1,200 black girls and 1,170 white girls who were enrolled in the National Heart, Lung and Blood Institute Growth and Health Study. Sue Kimm, MD, MPH, of the University of Pittsburgh School of Medicine, and colleagues followed the study subjects for 10 years, from childhood to late adolescence. The researchers asked the girls about their leisure-time activity several times during the study period.

Black girls reported getting less exercise than white girls at all ages. The frequency of physical activity decreased during the study period among both blacks and whites, but the decline was particularly steep among black teenagers. By the eighth year of the study, when the subjects were 16 or 17 years old, 56 percent of black adolescent girls and 31 percent of whites reported that they did not engage in any physical activity during their free time.

"Two things astonished us: the extent of the decline in eight years' time, and the prevalence of inactivity," Kimm told The Nation's Health.

The study authors identified certain risk factors associated with low physical activity levels. Girls who had a high body mass index at a young age became less active during the study period. Parental education was another factor: daughters of parents with a high school education or less were less likely to be physically active than girls who had at least one college-educated parent. Among older adolescents, reduced physical activity was linked to pregnancy in black teens and to cigarette smoking in whites. However, those factors did not account for the majority of the decline in activity.

The study authors concluded that the decline in physical activity among teenage girls was a serious health risk, particularly given the recent rise in obesity rates among young people.

Another study published in the same issue of the journal highlighted the importance of exercise for women. JoAnn Mason, MD, DrPH, of Harvard Medical School, and colleagues assessed the impact of physical exercise on cardiovascular disease risk in women. The researchers followed 73,740 women ages 50 to 79 and examined the association between physical activity levels and cardiovascular disease.

Higher levels of physical activity were strongly associated with reduced cardiovascular disease risk. Walking was as protective against heart disease as more strenuous forms of exercise: Women who either walked or exercised vigorously for at least 2.5 hours per week were approximately 30 percent less likely to develop heart disease than women who got less exercise, according to the study. Women who walked at a rapid pace -- greater than four miles per hour -- were at even lower risk of cardiovascular disease. Furthermore, women who both walked and exercised vigorously were less likely to develop heart disease than those who engaged in only one form of exercise.

Conversely, women who were seated for 16 hours or more every day developed cardiovascular disease at a higher rate than those who were less sedentary.

Exercise was found to be beneficial for all women in the study, regardless of age, race, smoking status, socioeconomic status or body mass index.

For more information, visit the New England Journal of Medicine Web site at <http://content.nejm.org>.

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By Catherine Wright