EvidenceHealthVitaminsSupplementsVitamin DMinerals

Calcium plus vitamin D in postmenopausal women: more kidney stones, limited fracture benefit

Study type:: Large randomised, double-blind, placebo-controlled trial of daily calcium plus vitamin D3 in postmenopausal women (Women's Health Initiative CaD trial).
Topic:: Calcium and vitamin D supplementation
Added:: 2026-05-08
Status:: published

Strength of evidence

Moderate

Source

Jackson RD et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354:669–683.

In the Women's Health Initiative CaD trial, over 36,000 postmenopausal women were randomised to **calcium carbonate (1,000 mg elemental calcium) + vitamin D3 (400 IU/day)** or placebo for about 7 years. The supplement produced **only a small, statistically fragile reduction in hip fractures**, but led to a **significant increase in kidney stones** (nephrolithiasis) compared with placebo. This large RCT with hard endpoints provides **moderate-quality evidence** that common calcium–vitamin D supplement regimens can cause clinically relevant harm (kidney stones), while offering at best modest fracture benefit in this population.

Key findings

Participants: 36,282 postmenopausal women aged 50–79 years.
Intervention: daily **calcium carbonate (1,000 mg elemental Ca)** plus **vitamin D3 (400 IU)** vs placebo.
Follow-up: median ~7 years.
**Hip fractures**: Slightly lower incidence in the supplement group, but the reduction was small and not unequivocally robust across analyses.
**Total fractures**: No large, clear reduction in overall fracture incidence.
**Kidney stones (nephrolithiasis)**: **17% higher incidence** of kidney stones in the calcium+vitamin D group compared with placebo.
No major mortality benefit and no clear reduction in other hard clinical endpoints.

Background

Calcium and vitamin D supplements are widely marketed to postmenopausal women to "build strong bones" and prevent fractures. The Women's Health Initiative Calcium–Vitamin D (CaD) trial was one of the largest randomised tests of this strategy in a real-world population.

Methods

**Population:** 36,282 postmenopausal women, aged 50–79 years, from the Women's Health Initiative.
**Design:** Randomised, double-blind, placebo-controlled. Intervention group: 1,000 mg elemental calcium (as calcium carbonate) + 400 IU vitamin D3 daily. Control group: matching placebo.
**Duration:** Median follow-up of about 7 years.
**Endpoints (hard):** Hip fractures (primary), Total fractures, Kidney stones (nephrolithiasis), Mortality and other clinical events.

Results

**Hip fractures:** A small relative reduction in hip fracture incidence in the supplement group, but the absolute difference was modest and of borderline statistical robustness.
**Total fractures:** No strong, consistent reduction in total fractures.
**Kidney stones:** Participants receiving calcium + vitamin D had a **significantly higher incidence of kidney stones**: about **17% more nephrolithiasis** compared with placebo.
**Other outcomes:** No convincing reduction in overall mortality or major non-skeletal events attributable to the supplement.

Interpretation

This very large, long-term RCT in postmenopausal women shows that daily supplementation with **common doses of calcium carbonate (1,000 mg) plus vitamin D3 (400 IU)**: delivers at best a **small, clinically limited hip fracture benefit**, does **not** clearly reduce total fractures, and **increases the risk of kidney stones**.
From a WorthDay perspective: The trial has randomisation, blinding and long follow-up, hard clinical endpoints (fractures, kidney stones), and a large, representative sample. It therefore provides **moderate-quality evidence** that a very typical "bone health" supplement regimen (Ca + D) is **not benign**: nephrolithiasis is a clear, measurable harm, and fracture benefit is modest and may not justify that risk for many women.

Limitations

The intervention combined **calcium and vitamin D**; the study cannot fully disentangle which component contributes most to the increased kidney stone risk, although calcium is likely a major driver.
The vitamin D dose (400 IU/day) was relatively low by modern supplement marketing standards; results do not cover higher daily doses.
The population was postmenopausal women in the US; findings may not generalise to younger women, men, or individuals with severe baseline vitamin D deficiency.
Analyses of fracture subtypes and subgroups add complexity but do not overturn the main pattern: modest fracture effect, more kidney stones.

WorthDay perspective

S0056 adds another important piece to the vitamin D/cholecalciferol puzzle when viewed together with S0053, S0054 and S0055: **S0053 (VITAL):** vitamin D3 2,000 IU/day in generally healthy adults → **no major prevention** of cancer or cardiovascular disease. **S0054:** 500,000 IU annual mega-bolus in older women → **more falls and fractures**. **S0055:** higher monthly doses in older adults → **more falls** than a moderate dose. **S0056:** daily calcium + vitamin D3 in postmenopausal women → **more kidney stones**, limited fracture benefit.
Under the WorthDay Evidence Criteria, these trials collectively show that vitamin D (especially with calcium or in high/bolus doses) is **not a risk-free "sunshine pill"**, and routine supplement strategies for broad populations offer **little hard benefit** with **clear signals of harm** under several regimens.
For WorthDay users: Blind, long-term use of calcium–vitamin D supplements, particularly without clear deficiency or specific indication, should be viewed with scepticism. Focusing on foundational lifestyle Elements (light exposure, real food, movement) is likely more rational than hoping for "bone health in a pill" that comes with an elevated kidney stone risk.

Permalink: https://www.worth-day.com/science-compass/s0056-calcium-plus-vitamin-d-in-postmenopausal-women-more-kidney

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