It’s common knowledge that calcium is essential for healthy bones. The best way for the body to absorb calcium is through food sources but, sometimes, supplementation is necessary in those who have a deficiency or significantly greater need. If looking for a calcium supplement, you may be faced by several choices: this blog from our registered nutritional therapist Kat Bright mBANT CNHC clarifies the different options and reminds of the risk of taking too much calcium.
Do you need a calcium supplement?
The evidence for calcium supplements has become more nuanced than the “take calcium for strong bones” message. A large 2026 review published in the British Medical Journal (BMJ), pooling 69 trials and more than 150,000 adults, found that calcium and vitamin D supplements offered little meaningful protection against fractures for most older people living independently. That doesn’t mean calcium isn’t essential, but it does mean a supplement isn’t a guaranteed insurance policy for your bones nor is it a substitute for the bigger picture of bone health. Bone health is a complex issue and looking for the root causes and trying to slow down bone loss is an essential first step.
Link to heart disease
The cardiovascular concern that if you take too much calcium it will be stored in your arteries, relates to supplemental calcium taken in large single doses, not to calcium from food. That’s one of several reasons we must approach calcium intake through food first and only supplement to fill a gap. The evidence seems to point to doses of supplemental calcium over 1,000mg a day on top of dietary intake increases the risk of cardiovascular disease. Clearly, more is certainly not better when it comes to calcium.
How much calcium do you need?
In the UK, adults need around 700 mg of calcium a day from all sources. If you already have osteoporosis or poor bone health, that target rises to roughly 1,200 mg a day, as recommended for protecting bone at higher risk. Good food sources include dairy, tinned fish (with the bones), green vegetables such as kale and broccoli, seeds and nuts. Spinach is rich in calcium, but its high oxalate content means you absorb less of it so opt for kale, broccoli and watercress. I advise clients to use a nutrient tracker for a few days to see how much calcium they are consuming a day. If your diet falls genuinely short, a supplement to top up is reasonable.
The main calcium forms and what to look for
Calcium carbonate
This is the cheapest and most widely prescribed form and what is usually given on the NHS (often combined with vitamin D). It’s about 40% elemental calcium by weight, so you get a lot of calcium in a small tablet.
Carbonate needs stomach acid to be absorbed, which means it should always be taken with food never on an empty stomach. It’s also less well absorbed than citrate and more likely to cause bloating, wind and constipation.
As we get older, which is when bone health is also more likely to decline, our stomach acid can become reduced, so bear this in mind before taking calcium carbonate.
Calcium citrate
Citrate is absorbed roughly 20–25% more efficiently than carbonate and, crucially, it doesn’t depend on stomach acid to work so you don’t need to take it with food. It’s gentler on digestion for many people. The trade-off is that it’s only around 21% elemental calcium, so you need more tablets (or larger ones) to get the same dose. It also, usually, costs more.
Calcium bisglycinate
This form binds calcium to the amino acid glycine and doesn’t rely on stomach acid which tends to make it gentle on the gut.
Algae derived calcium
This is a plant-based calcium which suits vegan and vegetarian diets. This form doesn’t need stomach acid so, again, is a good option if you are older and / or have a sensitive gut.
MCHC (Microcrystalline hydroxyapatite)
This form delivers calcium and phosphate in a bone-like matrix, usually derived from bovine bone. Microcrystalline hydroxyapatite also provides additional minerals (magnesium, phosphorus, potassium, zinc) and proteins (osteocalcin, type I collagen, type I insulin growth factor I and II, transforming growth factor beta) associated with bone metabolism. Being bovine, it isn’t suitable for those who don’t eat meat.
Daily dose
Your body absorbs calcium most efficiently in doses of 500 mg or less at a time. Above that, the percentage absorbed drops off. So, if you need more than that each day, you’ll get more benefit splitting it into two smaller doses than taking it all at once. It’s important to check the elemental calcium figure on the label, as this is the amount your body actually works with, not the total weight of the compound.
Medications that affect calcium
Several common medications interfere with how much calcium you absorb or retain. This is worth knowing, because it can change which form suits you:
- Proton pump inhibitors and other acid reducers (eg omeprazole, lansoprazole) reduce absorption of calcium carbonate. Citrate, MCHC or an algae-based calcium is a better choice.
- Long-term corticosteroids (eg prednisolone) reduce calcium absorption and increase how much you lose in urine – one of the more significant medication effects on bone.
- Some breast-cancer treatments (aromatase inhibitors) lower oestrogen and accelerate bone loss.
- Over-replaced thyroid medication can contribute to bone loss over time.
- Loop diuretics (eg furosemide) increase calcium loss through urine.
Calcium effect on medications
It also works the other way around: calcium can block the absorption of thyroid medication (levothyroxine), bisphosphonates, some antibiotics and iron, so these should be taken several hours apart from your calcium. If you take any of these, it’s worth a conversation with your GP or pharmacist about timing.
Don’t take calcium in isolation
Calcium doesn’t work alone and a good supplement choice considers what goes with it:
- Vitamin D is needed to absorb calcium in the first place.
- Vitamin K2 helps direct calcium into bone and away from soft tissues like arteries.
- Magnesium supports calcium metabolism and is often under-consumed.
You don’t necessarily need all of these in one tablet, but it’s a reason to think about your overall intake rather than calcium on its own.
IMPORTANT
This article is for general information and isn’t a substitute for personalised medical or healthcare advice. If you take regular medication, have kidney issues or are unsure whether a supplement is right for you, check with your GP, pharmacist or a Registered Nutritional Therapist.