Jewish World Review Sept. 6, 2002 / 29 Elul, 5762




Physical Activity Among Teenaged Girls

By Robert A. Wascher, M.D., F.A.C.S.

http://www.NewsAndOpinion.com | In the current issue of the New England Journal of Medicine (NEJM) is a study that tracked the weekly physical activity levels of 1,213 African American girls and 1,166 Caucasian girls over a period of 10 years. The girls all entered the study at age 9 or 10, and were 18 or 19 years of age at the conclusions of the study.

Using a standardized measure of physical activity referred to as metabolic equivalents (MET), the study's authors found that the black girls exerted a median of 27.3 METs per week at the beginning of the study, while he white girls expended a median of 30.8 METs per week. Ten years later, the black girls reported a leisure-time median of 0 METs per week (a 100% decline), while the white girls reported 11 METs per week (a 64% decline). By age 16 or 17, 56% of the black girls and 31% of the white girls reported no regular periods of exercise activity outside of school.

Lower levels of parental education were associated with a greater decline in physical activity among the white girls at both the younger and older age ranges during the course of the study. For the black girls, parental education levels were associated with lower physical activity levels only among the older girls. Teen pregnancy was significantly associated with decreased physical activity levels among the black girls, but not among the white girls.

On the other hand, cigarette smoking among white girls correlated with reduced levels of activity, but not for black girls. Obesity was strongly correlated with decreased levels of physical activity among both black and white girls.

This study identifies a dramatic decline in leisure-time physical activity levels as girls pass through adolescence, and is particularly striking among the African American girls who participated in this National Heart, Lung and Blood Institute study. While not all of the potential contributing factors to a decline in activity were addressed by this one study, it does, however, suggest that certain potentially modifiable behaviors appear to be involved.

Pregnancy, smoking, and progressive weight gain are the three areas that might be targeted in an effort to reduce physical inactivity. I suspect, however, that these three behaviors may, themselves, often result from other root causes. The idealization of the female body in our culture has resulted in an epidemic of eating disorders and suicide attempts (and other self-esteem related symptoms) among teenage girls who find themselves unable to live up to society's expectations.

Households with two working parents, or single parent households, require teenagers to act with greater independence, and often with lesser supervision than in previous eras. Teenage pregnancy and smoking no longer carry the social stigma that they did 10 or 20 years ago.

The gradual marginalization of physical education classes in public schools, and particularly for middle school and high school girls, has further reduced both the motivation and the opportunity for young girls to develop the habit of engaging in regular exercise.

Finally, the same factors that have resulted in over 60% of adult Americans becoming overweight are also affecting our youngsters. Harried lifestyles combined with easy access to cheap high-fat high-calorie food, the prevalence of effort-saving appliances, and a growing preference for leisure-time activities that are sedentary in nature are all contributing factors to inactivity and obesity.

WALKING WOMEN & CARDIOVASCULAR DISEASE

There is a large body of evidence to support the cardiovascular benefits of regular and moderate exercise in men. Women, who tend to experience fewer heart attacks than men during middle age, have not been studied as extensively as men. In this week's NEJM is a study that compared the cardiovascular effects of walking with more vigorous exercise in 73,743 postmenopausal women aged 50 to 79 years. The study also addressed the impact of prolonged sitting upon cardiovascular health. All study volunteers were free of known cardiovascular disease or cancer at the outset of the study.

Not surprisingly, increasing levels of physical activity were associated with a decreased incidence of heart attack and other signs of coronary artery disease, and these results held up for both black and white women irrespective of age or body mass. The women who were in the top 20% in terms of weekly physical activity experienced a 53% reduction in the clinical incidence of coronary artery disease when compared to the women in the bottom 20%.

Frequent walking and vigorous aerobic exercise were both associated with a similar degree of reduction in the risk of cardiovascular disease. A brisker walking pace and a fewer number of hours spent sitting were also predictive of a lower risk of cardiovascular disease. Bottom line: even relatively modest regular exercise, such as walking at a brisk pace, can pay large dividends in terms of cardiovascular health. On the other hand, too much time spent glued to a chair or sofa will significantly increase your risk of coronary artery disease.

C-REACTIVE PROTEIN & ESTROGEN REPLACEMENT THERAPY

Recently, the Women's Health Initiative study reported that, contrary to previous belief, estrogen replacement therapy (at least when combined with progesterone) appears to actually increase the risk of coronary artery disease. Previous studies have found no apparent reduction in the incidence of heart disease among women taking estrogen alone. One mechanism that has been postulated whereby estrogen replacement therapy might increase the risk of heart disease is through an increase in blood levels of C-reactive protein (CRP).

CRP is a protein that plays an important role in the inflammatory process, and elevated levels of CRP in the blood are now known to be linked to an increased risk of developing coronary artery disease (in addition to directly lowering cholesterol and LDL levels, the statin drugs also appear to lower levels of CRP in the blood). As reported in the current issue of the journal Circulation, a study was performed that compared the effects of conjugated oral estrogen pills (the most common form of estrogen replacement taken by postmenopausal women) with a skin patch that slowly releases a form of estrogen known as estradiol.

A total of 189 women were included in the study, and were randomized to receive either the oral estrogen pills or the transdermal estradiol patch. All women also received a progesterone pill as well, to protect them from developing estrogen-induced uterine cancer. In the women receiving the oral estrogen pills, CRP levels increased, on average, by 48% after 6 months. The women who received the estradiol patch, however, experienced a more modest 10% increase in CRP levels.

At one year, the women receiving oral estrogen had CRP levels that were 64% higher than were present at the beginning of the study, while the women who used the estradiol patch experienced a 3% increase in blood CRP levels. While these results do not prove that oral estrogens increase the risk of heart disease solely through elevated CRP levels (or that transdermal estradiol can prevent this adverse estrogen-related effect), this study nonetheless strongly suggests that such a mechanism may in fact be in play. The scientific evidence linking rising blood levels of CRP with increasing incidences of heart disease is expansive and solid. Whether or not the transdermal form of estrogen actually minimizes the risk of estrogen-related heart disease requires additional study.

The impact of the transdermal estradiol patch on the risk of breast and ovarian cancer, also needs to be thoroughly studied as well.

JWR contributor Dr. Robert A. Wascher is a senior research fellow in molecular & surgical oncology at the John Wayne Cancer Institute in Santa Monica, CA. Comment by clicking here.

Up

08/30/02: Babbling babies & brain function; homocysteine levels, vitamins & coronary artery disease; St. John's Wort & chemotherapy

08/16/02: A New Weapon Against Anthrax?; cataracts & motor vehicle accidents; gingko biloba takes a hit; air pollution & heart function during exercise; breast cancer genes & the estimated risk of breast cancer

08/09/02: Botulinum Toxin & Post-Stroke Spasticity; Intestinal Hormone Kills Appetite; Bone Marrow Cells Improve Blood Flow in Vascular Disease; Effectiveness of Restraining Orders on Domestic Violence

08/02/02: Mammography Saves Lives!; Obesity & the Risk of Heart Failure; High Sugar Diets & the Risk of Colon Cancer; Abuse During Childhood & Possible Effects of Genes on Antisocial Behaviors

07/26/02: Cancer: Nature vs. Nurture; Cardiorespiratory Fitness & Inflammation; Kidney Transplants from Cadaver Donors; Aircraft Cabin Air Recirculation & the Common Cold

07/19/02: PCBs & the Gender of Babies; Breastfeeding & the Risk of Breast Cancer; More Bad News About Hormone replacement Therapy

07/12/02: A cancer surgeon's perspective on hormone replacement therapy

07/08/02: Hormone replacement therapy & the risk of disease; more good news about statins; antioxidant vitamins & disease prevention; more

06/28/02: Antioxidants & the Risk of Alzheimer's Disease; Effects of Exercise on the Hearts of Patients with Mild Hypertension; Statins reduce cardiac events following angioplasty; more

06/21/02: Sex & violence and Advertising: Do Advertisers Get What they Pay For?; Don't Drink the Water (or the Salsa Either!); Vasectomy & Prostate Cancer Risk; Update on Smoking & Disease

06/14/02: Young Men, Obesity & Heart Disease; Breastfeeding & Obesity; Irritable Bowel Syndrome & rectal pain threshold; more data on cox-2 inhibitors & cancer; more

06/07/02: New coronary artery stent reduces risk of restenosis; possible cause of Parkinson's Disease identified; more

05/31/02: New biological insights into obesity & weight loss; broccoli kills cancer-causing stomach bug; anti-inflammatory drugs and the risk of heart attack

05/24/02: Molecular detection of tumor cells in the blood & prognosis; Cox-2 & breast/lung cancers; BRCA2 gene mutations & the risk of breast cancer; breast density & the risk of breast cancer

05/19/02: Moderate alcohol intake and blood sugar levels; more good news for tea drinkers; blood potassium levels & the risk of cardiovascular disease; ethnic differences in diabetic complications

05/10/02: Tea drinkers and the risk of death following heart attack; duration of breastfeeding & adult intelligence; abdominal aortic aneurysms: surgery or observation?

05/03/02: Risk of adverse drug reactions from newly released medications; preoperative beta-blockers may reduce heart bypass deaths; shape-shifting plastics may alter surgical practice; weight loss supplement may cause liver damage
04/26/02: Angry young men & risk of premature cardiovascular disease; stay-at-home dads & risk of cardiovascular disease; more on the effects of statins; dairy consumption and the risk of pre-diabetes; smallpox vaccine: good to the last drop?
04/19/02: Change your sex by drinking water?; Anti-inflammatory RXs may reduce growth of breast cancer cells; radiation treatment reduces repeat narrowing of bypass grafts
04/05/02: Fish & Omega-3 fatty acid consumption and cardiac health; news briefs
04/05/02: Can coffee reduce your risk of tooth decay?; exercise & blood pressure; a single high-fat meal reduces coronary artery function
04/01/02: Pre-diabetes: a newly defined category of health risk; teen television viewing and subsequent aggressive behavior; the benefits of strength training in the elderly; more ...
03/22/02: Bacteria, antibiotics & heart disease; mammograms: the debate continues; calcium & the risk of colon cancer ... and more
03/15/02: Mammography debate continues; statins & fracture risk; physical fitness & the risk of death; other intriguing findings
03/08/02: Blows to the chest & sudden cardiac death; air quality & the risk of lung cancer; tomatoes and your prostate
03/01/02: Diet & the risk of ovarian cancer; lifetime risk of developing high blood pressure; Osteoporosis prevention with a once-a-year injection?
02/26/02: The continuing controversy regarding screening mammography
02/22/02: Lowering body temperature after heart attack improves outcome; A silver lining for the chronically sleep-deprived?
02/15/02: Hormone replacement therapy & the risk of breast cancer; use it or lose it: Alzheimer's disease & cognitive stimulation; stress, divorce & death; child daycare, infections & parental guilt
02/08/02: Possible breakthrough in early cancer diagnosis; mammography: the controversy continues; CPR techniques revisited
02/01/02: Antibiotics in livestock feed & human disease; genetic detection of early colon cancer in the stool; genetic analysis of breast cancers may help decide treatment
01/25/02: Drug increases lifespan (if you're a fly...); workplace attitudes and smoking cessation; effects of inadequate sleep on surgeons
01/18/02: Lifelong effects of premature birth; smokers under the knife; aspirin and cardiovascular health
01/11/02: Estrogen levels in the blood & breast cancer risk; Heart attack: sex and survival; dangerous lettuce invaders
01/09/02: Cancer & aging: Two sides of the same coin?
01/04/02: Vitamin a & the risk of hip fracture in postmenopausal women; ovarian cancer risk and oral contraceptives
12/28/01: Magnetic Resonance Imaging (MRI) detects coronary artery disease; new development in obesity research; adverse childhood experiences & the risk of suicide attempts
12/21/01: Vaccination of children controls hepatitis a in the community; a possible cure for sickle cell disease; leptin and the risk of heart attacks
12/14/01: Chernobyl and the Risk of Thyroid Cancer in hildren; children & obesity; gastroesophageal reflux disease update
12/07/01: Update on school shootings; new implantable heart-assist device approved for further evaluation; prevention of fungal infections in pre-term babies
11/30/01: Flu vaccination in asthmatics; low-tar cigarettes are not less harmful; beans and your heart
11/21/01: Modified smallpox vaccine may reduce risk of cervical cancer; New approach to breast cancer diagnosis; New non-invasive prenatal diagnostic test for down's syndrome
11/16/01: Cholesterol-lowering drugs reduce risk of heart attack; supplemental radiation therapy reduces risk of breast cancer recurrence; brains of women may answer age-old questions
11/09/01: Bio-warfare (redux); my gray matter is bigger than yours; mad elk disease?
11/02/01: Making sense of bio-warfare
10/26/01: The impact of mammography on deaths due to breast cancer; diet & exercise may slow cancer cell growth; antidepressants and the risk of heart disease
10/19/01: New insights into autism; the wiley appendix
10/12/01: More bad news about obesity links to other diseases…Hey dad, can I borrow the car keys?
10/05/01: California leads nation in reduction of tobacco-related disease; exercise as an antidepressant?
09/25/01: Advances in the detection of breast cancer; primary care physician awareness of peripheral arterial disease; arsenic in the water
09/17/01: In perspective
09/12/01: Genes may hold secret to long life; men and women: cognitive function in the elderly; physical activity, obesity and the risk of pancreatic cancer
09/05/01: English milk cows prefer Beethoven and Simon & Garfunkel over Bananarama; new prostate cancer prevention study: looking for a few good men; exercise & diet can help prevent diabetes
08/28/01: Arthritis drugs may be linked with increased risk of heart disease; errors in blood clotting tests can be fatal; infant soy formula not associated with reproductive side effects

© 2002, Dr. Robert A. Wascher