Is calcium safe?

Within the upper limit, most adults tolerate it, but some risks are still debated. In placebo-controlled trials reviewed by EFSA, the EU food safety authority, 2,500 mg a day from food and supplements together was tolerated without adverse effects.^[1] The US upper limit is 2,500 mg a day up to age 50 and 2,000 mg from age 51.^[2] The risks that are discussed most are:

• Stomach problems. Gas, bloating and constipation are possible. Calcium carbonate appears to cause more of them than calcium citrate.^[2]
• Kidney stones. In the largest trial, 1,000 mg of calcium with vitamin D a day raised the risk by 17%.^[3] A review in people with osteoporosis did not find a significant increase.^[4]
• Heart. Reviews disagree. One found 15% more cardiovascular disease in healthy women after menopause,^[5] and another found no link with heart attack, stroke or death.^[6]
• Prostate cancer. Some cohort studies link high calcium intake with a higher risk, but not when the calcium comes from supplements.^[2] EFSA found no established link.^[1]
• Lead. Dolomite, bone meal and natural carbonate products had more lead in the past than refined forms. The gap has closed considerably since 2000, but some products can still have too much.^[7]
• Medicines. Calcium lowers the absorption or blood level of levothyroxine, quinolone antibiotics and dolutegravir, and can add to the risk of high blood calcium with lithium.^[2]

People who take a medicine every day, have had kidney stones, have kidney disease or have high blood calcium should ask a doctor or pharmacist first.^[2][3][8]