Estrogen and peptide YY are associated with bone mineral density in premenopausal exercising women

Background: In women with anorexia nervosa, elevated fasting peptide YY (PYY) is associated with decreased bone mineral density (BMD). Prior research from our lab has demonstrated that fasting total PYY concentrations are elevated in exercising women with amenorrhea compared to ovulatory exercising women. Purpose: The purpose of this study was to assess the association between fasting total PYY, average monthly estrogen exposure and BMD in non-obese premenopausal exercising women. Methods: Daily urine samples were collected and assessed for metabolites of estrone 1-glucuronide (E1G) and pregnandiol glucuronide (PdG) for at least one menstrual cycle if ovulatory or a 28-day monitoring period if amenorrheic. Fasting serum samples were pooled over the measurement period and analyzed for total PYY and leptin. BMD and body composition were assessed by dual-energy X-ray absorptiometry. Multiple regression analyses were performed to determine whether measures of body composition, estrogen status, exercise minutes, leptin and PYY explained a significant amount of the variance in BMD at multiple sites. Results: Premenopausal exercising women aged 23.8±0.9years with a mean BMI of 21.2±0.4kg/m ² exercised 346±48min/week and had a peak oxygen uptake of 49.1±1.8mL/kg/min. Thirty-nine percent (17/44) of the women had amenorrhea. Fasting total PYY concentrations were negatively associated with total body BMD (p=0.033) and total hip BMD (p=0.043). Mean E1G concentrations were positively associated with total body BMD (p=0.033) and lumbar spine (L2-L4) BMD (p=0.047). The proportion of variance in lumbar spine (L2-L4) BMD explained by body weight and E1G cycle mean was 16.4% (R ²=0.204, p=0.012). The proportion of variance in hip BMD explained by PYY cycle mean was 8.6% (R ²=0.109, p=0.033). The proportion of variance in total body BMD explained by body weight and E1G cycle mean was 21.9% (R ²=0.257, p=0.003). Conclusion: PYY, mean E1G and body weight are associated with BMD in premenopausal exercising women. Thus, elevated PYY and suppressed estrogen concentrations are associated with, and could be directly contributing to, low BMD in exercising women with amenorrhea, despite regular physical activity.