The study included a younger group, averaging 12.8 years of age, and an older group averaging 15.8 years; the allowed "for the observation of longitudinal changes from early to mid adolescence and mid to late adolescence."

Girls in both groups spent less time in moderate to vigorous physical activity as they got older, the researchers found. The younger set of girls were active for 5.9 hours a week, but their activity dropped to 4.9 hours weekly when they reached high school age. Among the older group of girls, average time spent being moderately to vigorously physically active fell from 5.1 hours to 3.5 hours a week. Among boys, however, time spent being active only fell among the older teens, from 6.5 to 5.1 hours per week.

Computer activity showed the sharpest increase among boys; from 11.4 hours to 15.2 hours weekly for the younger teens, and from 10.4 to 14.2 hours a week among the older boys. For girls, the only increase in computer use was seen among the older group, from 8.8 to 12.5 hours a week.

"Although technologic advances long have been credited for declines in occupation-related physical activity, these are among the first data-driven findings to suggest that such changes have an important impact on leisure time activity, particularly among youth," the researchers write.

They conclude: "Developing effective health promotion strategies that address a wide array of changing behavioral patterns will be important in promoting long-term health and active lifestyles among adolescents and young adults."

SOURCE: Pediatrics, December 2006.

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Heavier men have lower PSA levels, study shows

Last Updated: 2006-12-11 15:22:25 -0400 (Reuters Health)

NEW YORK (Reuters Health) - On average, men's levels of prostate-specific antigen (PSA) decrease as their body mass index (BMI) rises, a new study shows.

PSA is a marker for prostate cancer risk when levels are abnormally high. However, the findings are not likely to have a major influence on the usefulness of PSA as a cancer screening test, Dr. Jay H. Fowke of Vanderbilt University Medical Center in Nashville and colleagues conclude.

Past research has suggested that men with higher BMIs might have lower PSA levels, Fowke and his team note in the medical journal Cancer, while white men may have lower PSA levels, on average, than blacks. To investigate how BMI and ethnicity influence PSA, together and separately, the researchers looked at 150 African-American men and 149 whites, none of whom had been diagnosed with prostate cancer. Study participants ranged in age from 40 to 79.

As BMI rose, the researchers found, PSA levels declined, with the average level for lean men 22% higher than for obese men. The relationship was seen in blacks and whites, and was stronger among men younger than 60. Blacks' PSA levels were roughly 40% higher than whites', but there was no difference in the influence of BMI on PSA between blacks and whites.

The differences seen in the study would likely be relevant only in situations where obese men have somewhat elevated PSA levels, on the borderline of suspicion for prostate cancer, and who have to decide whether to undergo a biopsy to test for prostate cancer, Fowke and his colleagues write.

While some researchers have suggested ethnic differences in PSA levels may be due to body size, they add, their findings suggest that ethnicity's influence on PSA is independent of BMI.

SOURCE: Cancer, November 15, 2006.

Copyright © 2006 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.