Quick answer

Gas, bloating and other stomach complaints are the side effects most often linked to calcium supplements, and calcium carbonate causes them more often than citrate. Smaller doses taken with meals help. Total calcium from food and supplements should stay under the adult upper limit of 2,000 to 2,500 mg a day, and research on the heart is mixed.^1,2,3

Key facts

Splitting the dose, taking it with meals or changing forms can ease stomach side effects.¹
The upper limit is 2,500 mg a day for adults up to 50 and 2,000 mg from 51, counting food.²
High blood calcium is rare in healthy people and usually comes from an underlying medical problem rather than from diet.¹
In trials, calcium supplements did not change body weight or body fat.¹

Stomach and bowel effects

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

As a medicine, calcium carbonate can cause upset stomach, vomiting, stomach pain, belching, constipation, dry mouth, increased urination, loss of appetite and a metallic taste.⁴

A 2025 review by a long-time researcher of calcium supplements describes these effects as common and sometimes serious. Taking calcium with food, keeping each dose to 500 mg or less, or moving from carbonate to citrate are the usual fixes.^1,3

Getting too much calcium

High blood calcium is rare in healthy people and usually comes from conditions such as overactive parathyroid glands or cancer rather than diet. It can cause poor muscle tone, kidney problems, constipation, nausea, weight loss, tiredness, frequent urination and abnormal heart rhythms.^1,2

Calcium carbonate antacids provide about 270 to 400 mg of calcium in each chewable tablet or soft chew, depending on strength.¹

Calcium is easy to stack without noticing: a supplement, a multivitamin, fortified juice and a few antacid chews can together pass the upper limit. Add up every source on the Supplement Facts and Nutrition Facts panels.^1,2

Kidney stones

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

The trial tested supplements; it did not test calcium from food. If you have had kidney stones, ask your doctor before taking a calcium supplement.⁵

The heart question

Research on calcium supplements and the heart is mixed. A meta-analysis of 14 trials in 28,935 postmenopausal women found 15% more cardiovascular disease with 500 to 2,000 mg a day, while an expert panel judged that calcium within the upper limit neither raises nor lowers heart risk.¹

A 2025 review by a long-time researcher of calcium supplements reports that one dose raises blood calcium for about 8 hours, and that trials link supplements, but not calcium from food, to a 10% to 20% higher risk of heart attack.³

Over 22 years of follow-up in the Women's Health Initiative, women given calcium and vitamin D had a 6% higher risk of death from cardiovascular disease. Yet a panel convened by the National Osteoporosis Foundation and the American Society for Preventive Cardiology concluded that calcium within the upper limit is safe from a heart standpoint. If you have heart disease, talk to your doctor before taking a supplement.¹

Prostate

Some studies link high calcium intake, mainly from dairy, to prostate cancer. In a meta-analysis of 750,275 men, risk rose 2% for each extra 400 mg a day of total calcium, but calcium from supplements was not linked.¹

Medicines calcium can affect

Calcium binds several medicines in the gut and lowers how much is absorbed: levothyroxine, quinolone and tetracycline antibiotics, bisphosphonates such as alendronate, and dolutegravir. Long-term lithium can raise blood calcium, which supplements could add to. MedlinePlus advises keeping calcium carbonate apart from other medicines in general.^2,4,6,7

Weight

A review of 41 trials in 4,802 adults found that calcium supplements had no effect on body weight or body fat.¹

NIH describes the wider research on calcium and weight as mixed: some studies link higher intakes to less weight gain and others find no link. None of the evidence it reviews shows calcium supplements adding weight.^1,2

Questions people ask

Is it safe to take calcium every day?

Calcium is a daily nutrient, and the recommended amounts are meant to be met every day from food and supplements combined. Concerns rise with high supplement doses: stomach effects, more kidney stones in one large trial and a debated link to heart risk. Ask your doctor first if you have kidney or heart disease.^1,5

Is calcium safe for people with kidney disease?

Ask your kidney doctor first. MedlinePlus tells people who have or have had kidney disease to tell their doctor before taking calcium carbonate, and high blood calcium can itself harm the kidneys.^1,4

Can calcium cause constipation?

Yes, it is one of the most common complaints, more so with calcium carbonate. Spreading the dose through the day, taking it with meals or switching to citrate can help.^1,2

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