Vitamin D and Calcium Supplements Together

Quick answer

Vitamin D is needed for the gut to absorb calcium efficiently, which is why the two are often sold together. Adults need 1,000 to 1,200 mg of calcium and 15 to 20 mcg (600 to 800 IU) of vitamin D a day, and calcium is absorbed best in amounts of 500 mg or less at a time.^1,2,3

Key facts

The body needs vitamin D to absorb calcium through the main active route in the gut and to keep blood calcium in range.^1,2
Adults need 1,000 to 1,200 mg of calcium a day and 15 to 20 mcg (600 to 800 IU) of vitamin D, from all sources.^2,3
The body absorbs about 36% of a 300 mg calcium dose but only 28% of a 1,000 mg dose, so smaller doses spread through the day do better.¹
Most trials of vitamin D for bone also gave calcium, so the effect of each nutrient is hard to separate.⁴
In a trial of 36,282 women aged 50 to 79, 1,000 mg of calcium with 400 IU of vitamin D3 a day left hip bone density 1.06% higher than placebo after about 7 years.⁵

Why these two are sold together

About 98% of the body's calcium sits in the skeleton, where it forms the mineral that gives bones and teeth their hardness. The rest, a small pool in blood and tissues, lets muscles work, nerves send signals and blood clot. The body keeps that pool steady by drawing on bone when intake falls short, so a blood test does not show whether someone gets enough calcium.¹

The body needs vitamin D to absorb calcium through the main active route in the gut and to keep blood calcium in range.^1,2

Vitamin D is the key that makes the gut absorb calcium well. The liver and kidneys turn it into an active hormone, and that hormone tells the gut to take up calcium and phosphate, the raw materials of bone. Calcium also crosses the gut wall by passive diffusion, which carries a growing share as intakes rise, but vitamin D is required for the active route that does most of the work at lower intakes.^1,4

What the evidence shows

Our ingredient files grade the best-established statement for each nutrient and one trial-based statement for calcium. Note how modest the trial result is.^1,4

Needed to build and maintain bones and teeth*^1,2

Moderate evidence

A long-established role of the mineral, described by NIH. About 98% of the body's calcium sits in the skeleton, and the recommended amounts for adults were set at the intake needed to maintain bone. The skeleton is also the reserve the body draws on to keep blood calcium steady, so a shortfall shows up in bone over years rather than in a blood test.

Amount studied: Recommended intake: 1,000 mg a day for most adults, 1,200 mg for women over 50 and everyone over 70

Helps the body absorb calcium and maintain normal bones*^4,6,7

Moderate evidence

This is vitamin D's best-established role and the basis of official intake recommendations. It matters most when intake and sun exposure are low. In adults who mostly had adequate levels already, extra vitamin D gave no added benefit for bones: VITAL tested 2,000 IU a day in 25,871 people for about five years and found no difference from placebo.

Amount studied: The recommended 15 to 20 mcg (600 to 800 IU) a day from all sources; VITAL tested 2,000 IU a day on top of diet

Produces small gains in bone mineral density in adults over 50*^1,5,8

Moderate evidence

A meta-analysis of 51 randomized trials of calcium supplements in 12,257 people over 50 found bone density 0.7% to 1.8% higher at five skeletal sites, with similar gains from extra dietary calcium. The gain appeared within a year and did not grow after that; it was similar with or without vitamin D and at higher or lower doses, and the authors judged it too small to be likely to matter clinically. In the Women's Health Initiative, 1,000 mg of calcium with vitamin D a day left hip bone density 1.06% higher after about 7 years.

Amount studied: Calcium supplements from under 500 mg to over 1,000 mg a day, with or without vitamin D, for one to several years

What the combined trials can and cannot tell you

Most trials of vitamin D for bone also gave calcium, so the effect of each nutrient is hard to separate.⁴

This is why the Women's Health Initiative is so often cited. It gave 36,282 women 1,000 mg of calcium with 400 IU of vitamin D3 a day, and hip bone density was 1.06% higher after about 7 years. A meta-analysis of 51 trials in people over 50 found a similar small gain with or without vitamin D, and the authors judged it too small to be likely to matter clinically. NIH describes the trial results for bone density as mixed.^1,5,8

In people who already had adequate vitamin D levels, extra vitamin D alone gave no added benefit for bones in the 25,871-person VITAL trial. It matters most when intake and sun exposure are low.^4,7

How to take them, as far as the sources go

The two nutrients have complementary preferences about food. Calcium carbonate is absorbed best with food, calcium citrate is absorbed well with or without it, and vitamin D is best absorbed with a meal that has some fat.^1,3

The body absorbs calcium best in amounts of 500 mg or less at a time. Someone taking 1,000 mg a day from supplements does better with two smaller doses than one large one.^1,2

Calcium carbonate is 40% calcium by weight and is absorbed best when taken with food. It is also the calcium in many antacids.^1,2

Vitamin D is fat soluble, so it is best absorbed with a meal or snack that includes some fat. Some is absorbed even without fat.^3,4

Put together, a meal with some fat suits both, and a calcium dose of 500 mg or less is better absorbed than a larger one. NIH names no hour of the day for either nutrient.^1,3

Adding up the amounts

Calcium and vitamin D for adults, per day^1,2,3,9
	Calcium	Vitamin D
Recommended amount	1,000 mg; 1,200 mg for women from 51 and men from 71	15 mcg (600 IU); 20 mcg (800 IU) from 71
Upper limit	2,500 mg at 19 to 50; 2,000 mg from 51	100 mcg (4,000 IU)
What the limit counts	Food and supplements combined	Food, drinks and supplements
Typical supplement	500 or 600 mg, with or without vitamin D	Varies; 50 mcg (2,000 IU) in the largest trials

We do not sell a calcium supplement, so the card below shows only the products with vitamin D. Check the calcium in any antacid, multivitamin or fortified food you also use, since each counts toward the limit.

What’s in ours

Vitamin D3: Vitamin D-3, 50 mcg (2,000 IU) per serving, from the label
Men's Multi: Vitamin D, 10 mcg per serving, from the label
Ashwagandha Complex: Vitamin D3, 20 mcg per serving, from the label
Immune Support: Vitamin D3, 40 mcg per serving, from the label

Kidney stones, medicines and who should ask first

In the Women's Health Initiative, 36,282 women taking 1,000 mg of calcium and 400 IU of vitamin D a day had 17% more kidney stones than those on placebo over about 7 years. The upper limit was set on this evidence, although two later reviews of other trials found no such link.^1,5

Calcium supplements can cause gas, bloating, constipation or a mix of these. Carbonate causes them more often than citrate, especially in older adults with less stomach acid; smaller doses spread through the day, taking it with meals or switching forms can help.^1,2

Ask your pharmacist or doctor first

Thiazide diuretics, water pills such as hydrochlorothiazide, chlorthalidone and indapamide, reduce the calcium lost in urine. Together with vitamin D supplements, which raise calcium absorption, they might push blood calcium too high, especially in older adults and people with reduced kidney function or an overactive parathyroid gland. This applies to thiazides, not to every kind of water pill.^3,4

Expected from how the two work, not shown in studies

Ask your pharmacist how far apart to take them

Calcium carbonate can bind levothyroxine in the gut and reduce how much is absorbed. The levothyroxine label lists calcium carbonate among products to keep apart from the medicine, and a small study found calcium citrate and acetate had a similar effect; ask your pharmacist how to space them.^1,2,10,11,12

On the medicine's label

Ask your pharmacist how far apart to take them

Calcium supplements and antacids interfere with the absorption of bisphosphonates such as alendronate. The alendronate label tells patients to wait after their dose before taking any other medicine by mouth.¹³

On the medicine's label

Ask first if you have high blood calcium, kidney disease, kidney stones or an overactive parathyroid gland.^1,3
Ask first if you take levothyroxine, a quinolone or tetracycline antibiotic, a bisphosphonate, dolutegravir or lithium, each of which calcium can affect.²
Ask first if you take a thiazide water pill, a statin, steroid tablets, orlistat or a bile acid sequestrant, which can interact with vitamin D.³
Ask first if you have heart disease or have been told you are at high risk of it, since research on calcium supplements and the heart is mixed.¹
Ask first if you already take antacids, cod liver oil or a multivitamin, which add to both totals.^1,3

Questions people ask

Do you need vitamin D to absorb calcium?

Yes. NIH says vitamin D is required for calcium to be absorbed by active transport in the gut. Some calcium also crosses by passive diffusion, which carries more of the load as intakes rise.^1,2

Can you take calcium and vitamin D together?

They are sold together in many products and used together in the largest bone trials. The cautions are about totals and kidney stones, covered above, and about medicines that calcium can bind.^4,5

What is the best time to take a vitamin D and calcium supplement?

NIH names no hour for either. Calcium carbonate and vitamin D are both absorbed better with food, so take them with a meal that contains some fat, and keep each calcium dose to 500 mg or less.^1,3

Can calcium and vitamin D cause kidney stones?

In the Women's Health Initiative, women taking 1,000 mg of calcium and 400 IU of vitamin D3 a day had 17% more kidney stones over about 7 years than those on placebo. Anyone who has had stones should ask a doctor first.^4,5

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.