Table 4.

Comparison of trends in mean change in percent mammographic breast density after the one-year intervention among arms receiving vitamin D3 or placebo, according to baseline characteristics

Vitamin D3
Placebo1,000 IU/day2,000 IU/day3,000 IU/dayLinear trend in change in percent densitybInteractionb
Baseline characteristicsNChange in densityaNChange in densityaNChange in densityaNChange in densityaß (95% CI)PP
Serum 25(OH)D3c
 <50 nmol/L19–5.4 ± 1.224–5.6 ± 1.127–4.9 ± 1.032–4.0 ± 0.90.53 (–0.40–1.46)0.270.99
 ≥50 nmol/L77–5.8 ± 0.672–5.4 ± 0.672–6.2 ± 0.668–3.8 ± 0.60.52 (–0.02–1.06)0.06
Body mass index
 <25 kg/m262–6.5 ± 0.759–6.0 ± 0.763–6.0 ± 0.673–4.6 ± 0.60.59 (0.03–1.14)0.040.95
 ≥25 kg/m234–4.3 ± 0.937–4.5 ± 0.836–5.6 ± 0.927–1.7 ± 1.00.55 (–0.26–1.37)0.18
Total calcium intaked
 <1,000 mg/day57–5.8 ± 0.744–5.4 ± 0.848–6.0 ± 0.850–3.8 ± 0.70.55 (–0.08–1.19)0.090.92
 ≥1,000 mg/day38–5.8 ± 0.849–5.6 ± 0.747–5.9 ± 0.847–3.8 ± 0.80.60 (–0.10–1.30)0.09
Percent breast density
 <40%55–3.9 ± 0.752–4.0 ± 0.764–5.2 ± 0.661–2.6 ± 0.60.29 (–0.29–0.87)0.320.36
 ≥40%41–8.3 ± 0.844–7.1 ± 0.735–7.0 ± 0.839–5.9 ± 0.80.72 (0.02–1.42)0.04
Month of mammography
 October–February40–4.7 ± 0.840–4.8 ± 0.837–5.6 ± 0.939–3.2 ± 0.80.34 (–0.38–1.07)0.350.48
 March–September56–6.5 ± 0.756–5.9 ± 0.762–6.0 ± 0.761–4.2 ± 0.70.68 (0.08–1.28)0.03
Type of mammography
 CR53–6.4 ± 0.750–5.3 ± 0.849–5.4 ± 0.852–3.4 ± 0.80.90 (0.27–1.53)0.0060.10
 DR43–4.9 ± 0.846–5.6 ± 0.850–6.3 ± 0.848–4.3 ± 0.80.11 (–0.56–0.79)0.74
  • aMean ± SE of the difference between percent mammographic breast density at the end of the one-year intervention and that at baseline.

  • bß (95% confidence intervals) and P values for trend in mean change in mammographic breast density, and Pinteraction, are estimated from regression models. Study arm is treated as a continuous variable, and ß represents mean difference in change in percent mammographic breast density for increments of 1,000 IU/day vitamin D3. Models are adjusted for sites.

  • cMedian serum 25(OH)D3 was 39 nmol/L in the subgroup with baseline 25(OH)D3 <50 nmol/L, and 69 nmol/L in that with baseline 25(OH)D3 ≥ 50 nmol/L.

  • dAmong women who completed the C-DHQ1 at baseline (n = 380).