How much calcium do I need per day, and can too much be harmful?

Calcium requirements differ by life stage. Children aged 6 to 10 need 800 to 1200 mg per day. Teenagers and young adults up to age 24 need 1200 to 1500 mg, because that is when bone mass reaches its peak. Adult women up to age 50 and men up to age 65 get by with 1000 mg. Postmenopausal women not on hormone therapy and everyone over 65 have the highest requirement: 1500 mg per day. During pregnancy and breastfeeding the requirement is also 1200 to 1500 mg; the intestines double their absorption rate at that time, and during breastfeeding the body makes up part of the shortfall through temporary bone breakdown, which generally recovers after weaning.

A chronically low intake is a recognised cause of bone loss and osteoporosis. In older people living in care facilities, a daily combination of 1000 mg of calcium and 800 IU of vitamin D reduced the risk of fractures by roughly 30%. Vitamin D is indispensable here: without sufficient vitamin D, the intestine absorbs calcium less efficiently. Older people already have a lower absorption efficiency to begin with, which partly explains why their recommended intake is higher.

Up to 2000 mg per day is safe for most people. Above that level the risk of side effects increases. Whenever possible, obtain calcium from ordinary foods: dairy products, fortified plant-based drinks, and vegetables provide readily absorbed calcium. One caveat: drinking enough milk as a teenager to meet your calcium needs also delivers roughly 39 to 54 percent of the recommended maximum daily amount of sodium. This is worth keeping in mind, but it is not a reason to avoid calcium.

High calcium intakes inhibit iron absorption to a modest degree. In short-term studies, that absorption fell by an average of roughly 5.5 percentage points. However, no measurable effect on haemoglobin levels was found, and the long-term effects are contradictory. The evidence is too thin to support firm guidelines. If you have an iron deficiency, it may be wise not to take calcium and iron at the same time, although this is not an official recommendation.

Athletes, and especially female athletes who are not eating enough, face an elevated risk of calcium deficiency. Here too, aim to meet requirements through food. Supplements are useful when intake is demonstrably insufficient, preferably in consultation with a dietitian or sports medicine physician.