Calcium and Vitamin D3 and K2

Calcium is one of the few supplements where taking more than you need has a real downside, so these are the questions our naturopaths ask in store before recommending one.

A good fit if

• You eat little or no dairy and haven't switched to a fortified alternative
• You're postmenopausal or over 70, when your needs go up
• You're buying it together with vitamin D, which is where the evidence is strongest
• Your doctor has recommended it as part of a plan for your bones

Check with us first if

• You've had kidney stones, as randomised evidence shows a higher risk.
• You take lithium, which can raise blood calcium on its own.
• You take dolutegravir or another HIV antiretroviral, because calcium can greatly reduce how much of the medicine reaches your blood.
• You take thyroid medicine, antibiotics or iron, which all need to be taken a few hours apart from calcium.
• You already get plenty from food and would be adding a supplement on top.

• Calcium carbonate (item 1070). Best known for: Packing the most calcium into each tablet. Absorption: 40% actual calcium by weight. It needs stomach acid, so take it with food. Typical use: Allowed in listed medicines with no conditions at all.
• Calcium citrate (items 1073, 1074). Best known for: Absorbed without needing stomach acid. Absorption: About 21% actual calcium, so you need roughly twice the tablet for the same dose. Typical use: The form to choose if you take antacids or reflux medicine.
• Calcium amino acid chelate (item 1062). Best known for: The only calcium form with a legal cap on its make-up in Australia. Absorption: Calcium must be part of it, and how much is capped. Typical use: Check the actual calcium figure, which is usually low.
• Hydroxyapatite / MCHA (item 2643). Best known for: Calcium that comes from whole bone rather than a simple salt. Absorption: We found no head-to-head absorption trial. Typical use: Allowed in listed medicines as an active ingredient and a carrier (purpose codes A and E).
• Oyster shell calcium (items 3642, 3643). Best known for: A carbonate that comes from shells. Absorption: Works like carbonate, so it also needs stomach acid. Typical use: Must carry a mollusc allergen warning.

Reference values. The NHMRC recommended daily intake is 1,000 mg a day for men aged 19 to 70 and women aged 19 to 50, rising to 1,300 mg for girls and boys aged 12 to 18 and for older adults. Children aged 1 to 3 need 500 mg and those aged 4 to 8 need 700 mg. Babies have an adequate intake of 210 mg up to 6 months and 270 mg from 7 to 12 months.

Typical supplemental range. Australian labels usually carry 500 to 600 mg of elemental calcium (the actual calcium) per tablet, often with vitamin D. The elemental figure is the one that matters, not the weight of the compound. Carbonate is 40% calcium by weight and citrate about 21%, so a 1,250 mg carbonate tablet and a 2,400 mg citrate tablet give you roughly the same 500 mg.

Upper level. The NHMRC upper limit is 2,500 mg a day from all sources for everyone from age 1. No upper limit could be set for babies. Australia's permitted ingredients list (Schedule 1) sets no dose cap on the common calcium salts.

Worth knowing. Add what's on the label to what you already eat, because the upper limit counts food as well. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Dairy foods: the main Australian source of dietary calcium
• Bony fish such as tinned salmon and sardines: the bones are the calcium
• Legumes and some nuts: smaller contributions across the day
• Fortified soy drinks and cereals: fortification levels vary by brand; check the panel

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• You have had kidney stones. Randomised evidence shows harm: 1,000 mg of calcium carbonate with 400 IU of vitamin D3 increased kidney stones (HR 1.17).
• You take lithium. Long-term use can cause high blood calcium, and adding calcium supplements could increase that risk.
• You take dolutegravir or other HIV antiretrovirals. Calcium supplements can greatly reduce the level of the medicine in your blood.
• You are past menopause and take 1,000 mg/day of calcium as a supplement. A review of 13 double-blind, placebo-controlled trials in 28,935 people looked at heart and blood vessel outcomes, so talk to your doctor.
• High doses in general. Calcium supplements increased cases of high blood calcium in the colorectal adenoma trials.
• You are allergic to molluscs. Oyster shell (item 3643) and oyster (item 3642) must carry the exact warning "Contains mollusc" or "Contains mollusc products".
• The Upper Level. 2,500 mg a day from all sources, for everyone aged 1 and over.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before you start.