Calcium has a long history of being one of the most popular minerals and one of the most commonly used dietary supplements. It is still used for a wide variety of health problems. In Hungary, it’s used to treat certain diseases without any scientific basis. However, it has recently become clear that in most cases there is little benefit to supplementing it. If we consume enough calcium, supplementation can be harmful, but if one’s diet doesn’t contain enough, it may be worth supplementing.

The effect of calcium on bones

Most people take calcium to keep their bones healthy. Since bones are rich in calcium, it seems logical to assume that supplementation would strengthen them, but it is not that simple; many people have a high calcium intake to begin with, so there is no additional benefit to supplementing. What’s more, the body is good at regulating calcium absorption and if there is too much it will simply reduce it.

As for absorption itself, it’s important to have a good vitamin D supply, as without vitamin D, calcium isn’tutilized either. (1) For calcium to eventually be absorbed into the bones, many other micronutrients are needed, including vitamin K and vitamin A. (2,3) Deficiencies of these are common, so it’s not surprising that calcium supplementation alone has not been found to be very effective; not even for bone health.

A meta-analysis of 26 randomised trials published in 2015 found that calcium supplementation didn’t reduce the number of bone fractures.(4) A study published 2 years later, based on 33 randomised trials, also found calcium supplementation to be ineffective, and that calcium intake alone even increased the risk of hip fractures by 50%, a finding also confirmed by an older review.(6) 

It can be effective when combined with vitamin D

Several studies have found benefits when calcium suppplementation was combined with vitamin D supplementation, although it’s important to note that vitamin D supplementation alone reduces the risk of fractures, so it’s questionable how much of a role calcium actually plays. (7) For those who consume enough calcium, it’s certainly enough to only take care of vitamin D supplementation.

In an older meta-analysis from 2007, using the two together reduced the risk of fractures by 12% and also improved bone density.  The most effective dosage was found to be over 800 IU per day of vitamin D3 supplementation and calcium supplementation of over 1200 mg per day. (8) A 2020 meta-analysis also found a benefit from their combined supplementation, which significantly improved bone density and reduced hip fracture risk. (9)

In conclusion, calcium supplementation on its own has not lived up to expectations, but started producing good results when combined with vitamin D. It’s likely that the lower a person’s calcium intake, the more beneficial supplementation will be, but levels of both vitamin D and other micronutrients should also be optimal.

The dangers of calcium supplementation

The fact that supplementing too much calcium can be a problem is hardly surprising; all micronutrients are useful up to the amount needed, but beyond that they can cause problems. It’s hypothised that oversupplemented calcium will start getting deposited in places in the body where it should not be, increasing soft tissue calcification, which may play a role in the development of certain cardiovascular diseases. Nothing proves this better than the fact that those with genetically higher calcium levels have a much higher risk of facing cardiovascular problems (10).

It’s not only the amount of calcium supplementation that can a problem: unlike food, supplements raise blood calcium levels more quickly, so it’s possible that they can increase calcification even if our daily intake does not exceed a healthy range.

A 2020 review study found that calcium supplementation increases the risk of cardiovascular disease by ~10-20%, whereas dietary calcium intake up to 200-1500 mg has no significant effect.(11) An earlier meta-analysis published in 2010 also found similar results: calcium supplementation significantly increased the risk of several cardiovascular diseases.(12)

So calcium supplementation has its risks, and should only be started if one’s not consuming enough through their diet. This is typically the case when someone is forced to follow a special diet that is too low in calcium—such as dairy-free or low FODMAP diets. What is the best way to supplement calcium, then?

How to supplement calcium?

People who consume an average of 800 mg of calcium a day don’t need to supplement at all. Even a smaller amount is probably sufficient if levels of vitamins D3, A and K, as well as magnesium, potassium and other minerals and trace elements are adequate.

For those who don’t consume enough calcium through their diet, it may be worth supplementing, but there are a number of problems with this. Supplementing with well-absorbed calcium may increase calcification due to the rapid rise in calcium levels mentioned earlier, while supplementing with meals may reduce absorption of other minerals.

The best solution is probably to supplement it with or shortly after meals, but it’s important not to supplement other minerals at the same time. Studies have generally found 1g or more calcium to be problematic, so 400mg a day is probably safe in any form if one’s diet makes it necessary.