Penn State Hershey Young Women's Health Study is an ongoing epidemiologic study of the determinants of cardiovascular, reproductive, and bone health in women. The study was initiated in spring 1990 with the enrollment of 112 healthy, premenarcheal adolescents who are representative of Caucasian females attending public schools in Pennsylvania.
Major Outcome Measures
The study participants were seen every six months during the first four years of the study and yearly thereafter. Bone and body composition measures have been made by dual energy x-ray absorptiometry, which quantitatively measures bone mineral density, percent body fat, and percent lean body mass. Reproductive hormones were measured from 24 hour urine samples during the first four years and from fasting serum samples, thereafter. (1,2) Cardiovascular health has been assessed by blood pressure measurements, waist/hip measurements, cardiolipoprotein profiles from fasting serum samples and by a variety of fitness measurements. We measure aerobic capacity by bicycle ergometry, physical activity by an integrated sports exercise history, and muscle strength by push-ups, curl-ups, hand grip, the wall-sit, and by Biodex instrumentation. Nutrition intake assessment is made from three-day prospective diet records completed by the participants and analyzed with Nutritionist V software.
Bone Acquisition During Adolescence
Since females gain 40-50 percent of their skeletal mass during adolescence, it is important to understand how this gain may be affected by lifestyle factors that may be modified to optimize peak bone mass. During the first year of the calcium supplementation program, we observed that the supplemented groups had significantly greater rates of bone acquisition. (3,4) However, these differences persisted only during the period of supplementation. At one year postintervention and thereafter, the supplemented and placebo groups were no longer different. (5) We were also able to assess adolescent bone gain as a function of total calcium intake -- that is, the sum of habitual dietary intake plus calcium supplements. We compared bone acquisition measures and peak bone mineral density of the subjects as a function of their average calcium intake during ages 12-20. No significant relationship between calcium intake between the range of 500-1900 mg/d with any of the bone measures was observed. (6) In contrast, we observed that physical activity and specific fitness measurements are positively associated with bone gain and particularly with bone mineral density of the hip. (17)
Bone mineral density (BMD) is widely used as a surrogate measure for bone strength as it is positively correlated (r = 0.7-0.8) with in vitro measures of bone strength. To provide us with a more direct measurement of bone strength of the individuals in our study population, we recently began a collaborative study with researchers at the Johns Hopkins University and at the Center for Locomotion Studies at the University Park Campus of Penn State to use new technology to measure bone geometry and bone structure from the dual energy x-ray absorptiometry scans. These measurements will provide important insight into relationships between bone size, bone structure, and bone strength.
Longitudinal endocrine measurements during ages 12-20 allowed us to construct a natural history of maturation of the female reproductive system. It had been previously thought that after each woman reaches menarche, it took several years to establish regular ovulation cycles. Our results indicate that this maturation occurs within months rather than within years. (15)
We've also been able to measure the natural history of oral contraceptive (OC) use in a typical population of healthy young women. By age 20, approximately half of the study population were using OCs. As OC use depresses ovarian estrogen and testosterone production, it was of considerable interest for us to determine the effect of OC use on bone acquisition and peak bone mass. This question was explored with a case-control research plan, and we determined that the contemporary generation of low dose OCs do not have any measurable impact upon adolescent bone acquisition or peak bone mass. Using the same research plan, we inspected relationships among OC use, weight gain, and percent body fat, as perceived weight gain and increased body fat are the most frequently given reasons by adult women for discontinuing OC use. Among our study population, there was NO effect of OC use on either weight gain or percent body fat. These findings are of clinical importance as they allow physicians who counsel young women about contraception to allay their fears about weight gain or changes in body composition. (18)
Many cross-sectional epidemiologic studies have shown that fruit and vegetable intakes are important in reducing coronary heart disease (CHD) in adults. We assessed fruit and vegetable consumption among our cohort and compared it to cardiolipoprotein profiles. We observed that fruit consumption was significantly correlated with increased fitness, decreased body fat and better cardiolipoprotein profiles. Further, the young women who are in the top 20 percent for aerobic capacity consumed, on average, four fruit servings per day. (10)
We also studied cardiovascular disease (CVD) risk factors in this cohort with respect to use of oral contraceptives (OC). As expected, the OC user group had lower serum levels of estradiol, testosterone, lutenizing hormone, and follicle stimulating hormone. Compared to the non-user group, the OC user group had higher total cholesterol, LDL-cholesterol, triglycerides, and total circulating cortisol levels. However, each of these values was within acceptable clinical ranges.
A lack of longitudinal nutrition data has prevented investigation of the development of nutrient intake patterns in young women. We used the data from 30 days of prospectively collected nutrient intake records for each subject as they progressed from age 12 to age 18 to determine whether their dietary patterns remain consistent or track. Rank and correlation analyses and longitudinal linear models were used in these analyses and they showed that the subjects did not track strongly with respect to any nutrient variable. (16) Application of these results crosses health, education, and behavioral realms. The absence of strong tracking of nutrient intake among teenage women implies that researchers must exercise caution when interpreting associations among nutrient intake and health outcomes in adolescent females.
- Lloyd T, Eggli DF: Measurement of bone mineral content and bone density in twelve year old Caucasian girls. J Nucl Med 33:1143-1143, 1992.
- Lloyd T, Rollings N, Andon MB, Demers LM, Eggli DF, Kieselhorst K, Kulin H,Landis JR, Martel JK, Orr G, Smith P: Determinants of bone density in young women: I. Relationships between pubertal development, total body bone mass, and total body bone density in premenstrual females. J Clin Endocrinol Metab 75:383-387, 1992.
- Lloyd T, Andon MB, Rollings N, Martel JK, Landis JR, Demers LM, Eggli DF,Kieselhorst K, Kulin HE: Calcium supplementation increases total body bone mineral density in adolescent girls. JAMA 270:841-844, 1993.
- Lloyd T, Andon MD, Rollings N, Martel JK, Landis JR, Demers LM, Eggli DF,Kieselhorst K, Kulin HE: Peak bone mineral density in young women. JAMA 270:2926, 1993.
- Lloyd T, Buchanan JR: Premenstrual osteoporosis: contributions of exercise and dietary practices. Dietary Fiber Plenum Press, New York, 1990, pp 89-104.
- Andon MB, Lloyd T, Matkovic V: Supplementation trials with calcium citrate malate:Evidence in favor of increasing the calcium RDA during childhood and adolescence. J Nutr 124 (S Suppl):1412S-1417S, 1994.
- Chinchilli VM, Martel JK, Kumanyika S, Lloyd T: A weighted concordance correlation coefficient for repeated measurement designs. Biometrics, 52:341-353, 1996.
- Lloyd T, Martel JK, Rollings N, Andon MB, Kulin H, Demers LM, Eggli DF,Kieselhorst K, Chinchilli V: The effect of calcium supplementation and Tanner Stageon bone density, content and area on teenage women. Osteoporos Int, 6:276-283, 1996.
- Lloyd T, Chinchilli VM, Rollings N, Kieselhorst K, Tregea DF, Henderson NA,Sinoway LI: Fruit consumption, fitness and cardiovascular risk factors in teenage women. Am J Clin Nutr, 67:624-630, 1998.
- Lloyd T, Johnson-Rollings N, Kieselhorst K, Mauger E: Dietary caffeine intake is not correlated with adolescent bone gain. J Am Coll Nutr, 17:454-457, 1998.
- Lloyd T, Chinchilli VM, Johnson-Rollings N, Eggli DF, Kulin HK: Body composition development changes of adolescent white females. Arch Pediatr Adolesc Med, 152:998-1002, 1998.
- Lloyd T, Eggli DF, Miller KL, Eggli KD, Dodson WC. Radiation dose from DXA scanning to reproductive tissues of females. J Clin Densitometry, 1:379-383, 1998.
- Lloyd T, Johnson-Rollings N, Chinchilli VM, Martel JK: Renton of healthy, teenage women in a longitudinal study: The Penn State Young Women's Health Study. J Clin Res Prac 1(1):33-39, 1999.
- Legro RS, Lin NM, Demers LM, Lloyd T. Rapid maturation of the reproductive axis during perimenarche independent of body composition. J Clin Endocrinol Metab 84(3):1-5, 2000.
- Cardamone-Cusatis D, Chinchilli VM, Johnson-Rollings N, Kieselhorst K, Stallings VA, Lloyd T. Longitudinal nutrient intake patterns of United States adolescent women: The Penn State Young Women's Health Study. J Adolesc Health 26:194-204, 2000.
- Lloyd T, Chinchilli VM, Johnson-Rollings N, Kieselhorst K, Eggli DF, Marcus R. Proximal femur bone density (BMD) of young women reflects their sports-exercise histories but not their teenage calorie intake. Pediatrics 106:40-44, 2000.
- Lloyd T, Taylor DS, Lin H-M, Matthews AE, Eggli DF, Legro RS. Oral contraceptive use by teenage women does not affect peak bone mass: A longitudinal study. Fertil Steril 74:734-738, 2000.
- Lloyd T, Taylor DS. Calcium intake and peak bone mass. J Am Med Womens Assoc 56:49-52, 2001.
- Lloyd T, Beck TJ, Lin H-M, Tulchinsky M, Eggli DF, Seeman E, Cavanagh PF. Contributions of exercise, fitness, body composition and calcium intake during adolescence to peak bone measures in young women. Bone 30(2):416-421, 2002.
- Lloyd T, Lin H-M, Eggli DF, Dodson WC, Demers LM, Legro RS. Adolescent Caucasian mothers have reduced adult hipbone density. Fertil Steril 77:136-140, 2002.
- Lloyd T, Lin H-M, Mathews AE, Bentley CM, Legro RS. Oral contraceptive use by teenage women does not affect body composition. Obstetrics and Gynecology in press.