Calcium supplements are one of the most common supplements out there. They’re often promoted for their potential benefits to bone health and are generally considered low risk. However, there is some discussion around possible negative effects on heart health.
This post will explore why there is talk about this and also where the evidence currently stands.
Proposed Mechanisms
Calcium supplements have been proposed to increase the risk of heart disease through several possible mechanisms:
- Higher Blood Calcium Levels: Taking calcium supplements can raise calcium levels in the blood, which stay elevated with long-term use.
- Calcium Build-Up in Blood Vessels: Elevated calcium levels from supplements might contribute to calcium deposits in blood vessels, which is a known factor for heart disease.
- Effects on Blood Clotting: Calcium plays a key role in blood clotting. Increased calcium levels might affect clotting.
What Does the Evidence Show?
We are fortunate to have a lot of large sample-size research on this topic.
Instead of going through each study, the main one that is worth focusing on is a 2021 meta-analysis of clinical trials.
It covered 13 double-blind, placebo-controlled randomised controlled trials. There were 28,935 participants in the intervention groups and 14,243 in the control groups.
The finding was that calcium supplements increased the risk of cardiovascular disease.
Specifically in healthy postmenopausal women, the increase in risk was 15%.
One big thing worth mentioning is that of 5 similar reviews looking at the topic, 3 found an increased risk and 2 found no increased risk.
At this stage, the evidence seems to be pointing towards a small but slightly inconsistent increased risk.
Dietary Calcium Differences
At this stage, these findings appear to be exclusive to calcium supplements. Dietary calcium does not appear to be an issue. There can be many explanations for this such as:
- Dosages in a single sitting are often smaller.
- Associated nutrients such as magnesium, phosphorus and vitamin K might reduce vascular calcification.
- Absorption might be slower due to integration with other nutrients in food.
- Calcium levels in the blood seem to rise less than they do with calcium supplements.
Do Calcium Supplements Even Reduce Fractures Risk
People linking calcium supplements with cardiovascular disease risk often highlight that the evidence for the reductions in fracture risk is weak.
This claim holds merit, but it’s worth discussing with nuance.
There are many examples of calcium supplements not reducing fracture risk.
A major one worth being aware of is a 2017 meta-analysis covering 33 RCTs, including more than 50,000 participants over the age of 50. This review on calcium and vitamin D supplementation found no reduction in fracture risk.
At a minimum, that highlights that we shouldn’t just be taking calcium supplements without context for that purpose.
Added Nuance on the Topic
It is possible to increase bone mineral density without necessarily translating to a meaningful reduction in fracture risk.
For example, a similarly large review on calcium supplementation found increases in bone mineral density in participants over the age of 50 of ~0.5-1.5%.
That is a small increase that is unlikely to do much to reduce fracture risk. A side note is that it’s impressive for people to increase bone mineral density at all later in life when most are resigned to just delaying decreases.
The next angle is that some people are more likely to benefit than others. This research is spread across people over the age of 50 without consideration of their current diet. People with low calcium intakes are more likely to benefit than those with high intakes.
And the older people get, the higher their fracture risk gets, and the more likely it is to see benefits translate too.
The reason for adding this nuance is to highlight that there can still be some scenarios where it makes sense. A food-first approach is always recommended where possible of course.
Alongside that, it’s also worth acknowledging that calcium is just one small component of bone health.
Vitamin K Has the Potential to Help Too
Vitamin K2 could help from multiple angles.
Research has found that it can help reduce vascular calcification. One main mechanism proposed is that it helps ensure calcium ends up in the bones rather than in other areas.
An observational study looking at coronary heart disease over an average of 11 years found higher vitamin K2 intake was associated with reduced risk of coronary heart disease.
The research is not all positive though. There are still some studies that have found no meaningful reductions in cardiac outcomes.
At this stage, the evidence looks mildly in favour of it helping.
Beyond that, it also helps with improving bone mineral density. So if that is the reason you are taking calcium, it is worth considering vitamin k2 as well unless your dietary intake of it is already good.
Interpretation
The evidence indicates that calcium supplementation might increase the risk of heart complications.
Either it’s not a risk OR it’s a small consistent risk.
Based on that, a safe interpretation is:
- If you are unlikely to benefit from calcium supplements, it is not worth taking them.
- If you ARE likely to benefit from them, it is worth weighing up the potential risk.
- If you were to take them, it’s also worth considering other options to potentially reduce that risk. Vitamin K2 is one of those options although the evidence is not consistent. But taking other actions to reduce your risk of cardiovascular disease makes sense too.
