A total of 260 of the 301 DISC female participants participated in the DISC06 Follow-Up Study. Of these, 30 were pregnant or breastfeeding within 12 weeks prior to or at their visits and were excluded from analyses. Characteristics of the remaining 230 participants are shown by DISC treatment group in . Approximately 90% of participants were White, 6% were Black and the remainder were other races. Participants’ ages ranged from 24.9 years to 29.7 years and did not differ by treatment group. Intervention and usual care group participants also did not differ in adiposity, menstrual and reproductive characteristics including age at menarche, number of full term pregnancies, and hormonal contraceptive use, or by cigarette smoking status. Every attempt was made to schedule DISC06 follow-up visits in the luteal phase of the menstrual cycle; 84% of intervention group participants’ visits and 80% of usual care group participants’ visits took place during the luteal phase.
Characteristics of DISC Intervention and Usual Care Group Participants at DISC06 Follow-Up Visits
Current diet composition at the DISC06 follow-up visit for the 218 participants who completed dietary recalls is shown in . Intervention group participants’ median reported energy intake was 1,602 kcal/day, which was slightly, but not statistically significantly, less than the median of 1,710 kcal/day reported by usual care group participants. The intervention group reported consuming a statistically significantly lower percent of calories as saturated fat compared to the usual care group; their median intakes were 9.8% and 11.3%, respectively. The intervention group also reported consuming a slightly lower percent of calories as total fat and monounsaturated fat and slightly less cholesterol/1000 kcal compared to the usual care group. In contrast, the intervention group reported consuming statistically significantly more dietary fiber compared to the usual care group. Reported intakes of polyunsaturated fat, protein and carbohydrates as percentages of calories did not differ by treatment group. Self-reported leisure-time physical activity levels at ages 14-17 years and over the past 12 months also did not differ.
Median Daily Nutrient Intakes and Leisure Physical Activity Levels of DISC Intervention and Usual Care Group Participants at DISC06 Follow-Up Visits
Estradiol, progesterone and SHBG were measured in serum from 87 participants who did not take hormonal contraceptives during the month before their DISC06 follow-up visit and who were in the luteal phase of their menstrual cycle. Unadjusted and adjusted mean hormone and SHBG concentrations are shown by treatment group in . Unadjusted serum estradiol concentrations did not differ substantially by treatment group. After adjustment for non-dietary variables, the intervention group's mean estradiol concentration was 131.3 pg/ml (95% confidence interval (CI) = 101.8-169.4 pg/ml), which was higher than the mean of 114.6 pg/ml (95% CI = 87.4-150.4 pg/ml) for the usual care group, but the difference was not statistically significant (p=.40). The difference became significant (p=.02), however, after further adjustment for current dietary fat and fiber intake; diet-adjusted mean luteal phase estradiol concentrations were 141.5 pg/ml (95% CI = 116.1-172.4 pg/ml) and 96.7 pg/ml (95% CI = 77.1-121.2 pg/ml) for the intervention and usual care groups, respectively. A similar pattern was observed for non-SHBG-bound estradiol, such that significant treatment differences were observed only after adjustment for current diet. No treatment group differences were observed for progesterone or SHBG in unadjusted or adjusted analyses.
Geometric Mean and 95% Confidence Interval (95% CI) for Serum Hormone Concentrations at Follow-up in DISC Intervention and Usual Care Groups
Treatment group differences in breast density were evaluated after excluding 13 scans on women who had breast implants or breast reduction surgery. Results based on the 182 participants who had scans available for inclusion in analysis are summarized by treatment group in . Breast density expressed as the percent of breast tissue that was dense or the volume of dense tissue did not differ significantly by treatment group in adjusted or unadjusted analyses. In unadjusted analyses, mean percent densities were 21.2% (95% CI = 17.1-26.3%) and 16.7% (95% CI = 13.6-20.5%) for intervention group and usual care group participants, respectively (p=.12). After adjustment for non-dietary variables, intervention group participants’ mean percent density was 20.2% (95% CI = 17.5-23.3%) compared to 18.3% (95% CI = 16.0-21.0%) for usual care group participants (p=.35). Further adjustment for current dietary fat and fiber intake did not alter results in a meaningful way. Results were similar when breast density was expressed as volume of dense tissue.
Geometric Mean and 95% Confidence Interval (95% CI) for Breast Density at Follow-up in DISC Intervention and Usual Care Groups
Whole-body BMC and BMD for 215 participants who had acceptable DXA scans are summarized in . Whole-body BMC did not differ by treatment group in unadjusted analyses. However, after adjustment for non-dietary variables intervention group participants had statistically significantly (p=.02) higher BMC compared to usual care group participants; their mean BMCs were 2,444 g (95% CI = 2,389-2,499 g) and 2,377 g (95% CI = 2,321-2,432 g), respectively. Further adjustment for current dietary fat, fiber, calcium and vitamin D intake increased the statistical significance of the treatment group difference (p=.003); diet-adjusted mean BMC was 2,448 g (95% CI = 2,395-2,502 g) for intervention group participants compared to 2,356 g (95% CI = 2,302-2,410 g) for usual care group participants. Treatment group differences in whole-body BMD generally showed the same pattern observed for BMC.
Mean and 95% Confidence Interval (95% CI) for Bone Mineral Content (BMC) and Bone Mineral Density (BMD) at Follow-up in DISC Intervention and Usual Care Groups
Women who were pregnant or breast feeding within 3 months of the visit were not included in the current analysis because of concerns about the potential effects of a recent pregnancy or breast feeding on biomarkers investigated, particularly serum hormone levels and breast density. To evaluate potential longer-term effects of pregnancy and breastfeeding, we repeated analyses limited to women who had not been pregnant or breastfeeding within 6 months prior to the visit and again restricted to women who had not been pregnant or breastfeeding within 12 months prior to the visit. Results of these subset analyses did not differ substantially from those presented for any of the biomarkers.