Interaction fact sheet
Vitamin D and calcium
Compatible combination, modest benefit, kidney stone risk to be aware of.
Vitamin D helps you absorb calcium. In a trial involving more than 36,000 postmenopausal women, the combination slightly increased hip bone density without clearly reducing fractures, and increased kidney stone risk by 17%.
In brief
- Mechanism
- Vitamin D increases intestinal calcium absorption.
- Magnitude
- Hip bone density +1%; no significant reduction in hip fractures; kidney stones +17%.
- Who is affected
- Older people, particularly those with vitamin D deficiency or low dietary calcium intake.
- What to do
- Meet calcium needs through food first; supplement only if intake is insufficient or on medical advice.
The largest trial
In the Women's Health Initiative trial, 36,282 postmenopausal women took 1,000 mg of calcium and 400 IU of vitamin D daily, or a placebo, for an average of 7 years. Hip bone density was 1% higher in the supplemented group. The reduction in hip fractures was not significant overall, but it was significant among women who actually took their tablets. The risk of kidney stones increased by 17%.
The takeaway
The combination makes sense for older people with deficiencies or who eat few calcium-rich foods. For everyone else, dietary calcium is preferable to tablets. A moderate daily dose of vitamin D, without calcium, is often enough to correct a winter shortfall.
In practice
What you can do
- Meet your calcium needs through food first: dairy products, calcium-rich water, vegetables, almonds.
- Only use calcium supplements if your intake is insufficient or they are prescribed.
- Avoid high doses of vitamin D without testing.
When to seek advice
- History of kidney stones before taking a calcium supplement.
- Osteoporosis: treatment involves more than calcium and vitamin D.
- Taking levothyroxine or an antibiotic? Take calcium at a separate time.
Main sources
- 01Jackson RD et al. Calcium plus vitamin D supplementation and the risk of fractures. New England Journal of Medicine, 2006. PubMed
Frequently Asked Questions (FAQ)
Should you take vitamin D with calcium?
Not necessarily. Vitamin D alone is often enough to correct a deficiency. Calcium supplements are mainly useful if your diet provides too little.
Do calcium tablets cause kidney stones?
In the large WHI trial, calcium combined with vitamin D increased kidney stone risk by 17%. Dietary calcium does not seem to have this effect.
What about vitamin K2 with vitamin D?
The combination is popular, but evidence of its benefits is limited. If you take a vitamin K antagonist anticoagulant, avoid K2 unless advised otherwise.