Magnesium 101

How Long Does Magnesium Stay in Your Body?

If you’re thinking of taking a magnesium supplement, you might be wondering how long magnesium stays in your body. The short answer is no more than a day or two. However, there are a couple of factors that could affect this timeline. Read on and we’ll break down how magnesium travels through your body and how long it takes…

How is magnesium absorbed?

All types of magnesium supplements are compounds of magnesium and another substance, e.g. glycine (magnesium glycinate). Assuming you’re taking your magnesium orally, e.g. via a tablet, drink, or powder, it will first hit the stomach. 

In your stomach, the supplement will be broken down into its individual parts and the magnesium molecules will then start to bond with water molecules. This is called ionization, and magnesium is said to be ionized as a result. The ionized magnesium will then make its way into the small intestine, where around 45% of the magnesium is absorbed.

After the magnesium passes through the small intestine, another 5% or so will also be absorbed through the large intestine. Again though, this depends on how bioavailable the magnesium is. Any magnesium that has not been absorbed will be excreted through your feces.

That magnesium you absorbed throughout your digestive tract enters the bloodstream. It’s then carried around your body and delivered to your cells, where it performs its many essential roles. Some magnesium will also be stored in the bones and other tissues. But because your body can only store so much magnesium, excess magnesium will ultimately be filtered out by your kidneys. 

All in all, within 24 hours of taking your magnesium supplement, you will have excreted around 70% of the magnesium content, either through feces or urine. 

What factors can affect magnesium absorption? 

The numbers given above are approximate figures, as there are lots of factors that can affect magnesium absorption, retention, and excretion. 

Regarding absorption, the actual amount of magnesium absorbed in the small intestine will depend on how “bioavailable” your supplement is. Magnesium cannot be absorbed unless it’s been ionized, and some types are more resistant to this process. For example, in magnesium oxide, the bond between the magnesium and oxygen molecules is very hard to break. That means that by the time it leaves your stomach and heads to the small intestine, much of the magnesium will not be ionized. Therefore, it’s not available to be absorbed. On the other hand, magnesium and malic acid (as magnesium malate) are easy to break apart, so there is much more ionized magnesium available for absorption when it reaches the small intestine. 

There’s also the issue of gut health. Some conditions affecting the gastrointestinal tract can make it difficult for magnesium to be absorbed as it travels through. These include ulcerative colitis, Crohn’s disease, and coeliac disease. Alcoholism can also affect the lining of the gut and slow down mineral absorption, So if you suffer from one of these diseases, your absorption rate will likely be lower than normal. 

But let’s say you absorb magnesium just fine. If you have a condition like diabetes, though, you might urinate a lot more, and you can end up passing more magnesium, at a faster rate, as a result. On the other hand, kidney failure and other kidney problems can actually cause you to retain too much magnesium over time, as they may not be able to get rid of excess magnesium as easily. 

To summarize…

For the average healthy person, your magnesium supplement will stay in your body for 24-48 hours. However, if you’re taking a type of supplement with low bioavailability, or you have health conditions that affect how you absorb or get rid of magnesium, you may find that your supplement sticks around for a longer or shorter duration.