Trial Information

A Randomized Double-blind Placebo-controlled Trial of the Effect of Vitamin D Supplementation on Breast Density in Premenopausal Women

OBJECTIVES

Primary:

- to determine whether adding oral supplementation with vitamin D3 (cholecalciferol) at
doses of 1,000, 2,000 and 3,000 IU/d to baseline total vitamin D intake over a period of 12
months reduces mammographic breast density among premenopausal women at moderate to high
risk of breast cancer who reside in the Quebec City area, Canada.

Secondary:

- to assess the net increase in 25(OH)D levels resulting from this vitamin D3
supplementation;

- to document the compliance with, and safety of, supplementation with tested doses of
vitamin D3 over one year.

OUTLINE This study is a double-blind, placebo-controlled, randomized trial among
premenopausal women who live in the Quebec City area and have ≥ 20% breast density at
baseline.

The intervention consists of the addition, over baseline total vitamin D intake from food
and supplements, of three different doses of vitamin D3 (1000, 2000 or 3000 IU/day) for a
period of 12 months. There are four arms in the trial:

- Arm 1: 1,000 IU vitamin D3/d (1 tablet vitamin D 1000 IU + 2 tablets placebo);

- Arm 2: 2,000 IU vitamin D3/d (2 tablets vitamin D 1000 IU + 1 tablet placebo);

- Arm 3: 3,000 IU vitamin D3/d (3 tablets vitamin D 1000 IU);

- Arm 4: placebo (3 tablets placebo/d).

Vitamin D tablets (1000 IU tablets) and the placebo tablets are undistinguishable in size,
shape, color and taste, and are manufactured by the same company.