Nutrition is all about context. It is often not as simple as “caffeine completely blocks calcium absorption while it is in your system.”
Typically, there is more nuance. How much of an impact does it have? What dosages of caffeine are required for this impact to be relevant? Does having more calcium offset this?
This is a bit of a niche nutrition topic. I still think it is relevant though.
I have been a dietitian for about 5 years now. And for my first couple of years, whenever I would be talking about calcium with a client, and they mentioned that they would use milk in their coffees I had a standard response. My typical response was something along the lines of “unfortunately caffeine inhibits calcium absorption, so we probably want a decent amount of calcium to be separate from caffeine.”
This is because I made the assumption from what I had read/heard/learned that calcium absorption was significantly inhibited by caffeine.
Around 3 years ago, I first questioned that advice though. After looking into the research on the topic, I changed my stance a bit. Caffeine DOES impact calcium absorption. But is it enough to be relevant in practice?
Where Does This Idea Come from?
There are a few places the claim that caffeine inhibits calcium absorption stems from. The main one is that there is evidence that urinary calcium excretion and intestinal calcium secretion are correlated with caffeine consumption.
Therefore, you could argue that absorption is reduced based on that logic.
The other aspect to consider is that epidemiological studies have shown mixed results.
Often in younger people, it does not seem to have made much difference in these studies. In older individuals, there seems to be a bit of a link between higher caffeine intake and lower bone mineral density.
Obviously, when talking about calcium absorption, bone mineral density is the outcome we really care about.
The flaw with epidemiological studies though is that they do not really account for controlled variables. For example, higher caffeine intake could be linked with lower bone mineral density, but does that mean caffeine is causing that issue?
As some studies have pointed out, higher caffeine intake is often linked with lower calcium intake on average too. Although not all the research supports this, higher calcium intake is likely beneficial for bone mineral density. It is hard to identify based on epidemiological studies whether calcium is playing the larger role, or caffeine.
How Does Caffeine Effect Calcium Absorption?
Caffeine related increases in calcium excretion through urine is mostly attributed to a reduction in resorption of caffeine in the kidneys.
Lower resorption means higher excretion.
This appears to be due to the effect on adenosine receptors in the kidneys due to the caffeine.
How Much Does Caffeine Impact Calcium Absorption By?
Now this is the key question.
The first study that really changed my mind on this topic revealed that the predicted calcium balance was -6mg/day for each 175mg/day increase in caffeine.
To break that down further:
- The RDI for calcium in Australia is 1000mg. For older individuals it increases to 1300mg.
- 6mg is pretty much nothing in comparison to an intake of 1000mg.
- 80mg of caffeine is roughly the equivalent of a coffee (although caffeine content of coffee is quite variable) or 250ml of an energy drink.
- Therefore, 175mg is roughly like just over 2x coffees or 500ml of energy drink.
This would mean that even at relatively high levels of caffeine intake at just under 400mg, it would still only explain a decrease in calcium balance of -6mg/day.
As a previously referenced study concluded, it would literally only take a few teaspoons of milk to offset that.
This is not just an isolated study either. A follow-up study on the topic came to the same conclusion too.
Caffeine DOES inhibit calcium absorption, just like I had learned and used to relay on to clients. But it honestly does not seem to matter in the slightest. The impact is so small. Not knowing that it inhibits calcium absorption would not change how you would do things at all.
There is an argument that older women do not seem to compensate adequately and that potentially their calcium balance situation would be slightly more significant. But this only seems relevant when calcium intake is below the recommended level.
Consuming a sufficient amount of calcium is the starting point. The RDI in Australia is either 1000mg or 1300mg depending on your age.
Most people do not seem to consume near that amount though. There are other factors that affect bone mineral density though. Getting sufficient exercise, vitamin D, vitamin K, phosphorus, potassium, magnesium, and other nutrients all help too.
Beyond that, I would not even think about doing anything special related to caffeine in terms of how it impacts calcium absorption. Previously I used to have clients separate at least some of their calcium intake from their caffeine intake, but with the knowledge above, it just does not seem to matter at all.