When Is The Best Time To Take Magnesium for Optimal Results?

Magnesium is an essential mineral with pivotal roles in the human body [1]. Maintaining healthy body magnesium levels is imperative to preserve healthy cellular function and to promote general health, better aging, brain health, and overall well-being. A healthy diet with plenty of magnesium-rich foods is the first step to do so, and magnesium supplements can be a great complement.* 

A common question regarding magnesium supplements is whether there is an ideal time of day to take them. In this article, we’ll look at what research says about the best time to take magnesium and the factors that may influence magnesium absorption and retention.

How Does Timing Affect Absorption?

Magnesium absorption in the intestines is known to be influenced by several factors. These include body magnesium status, the amount of magnesium ingested, the food matrix, and the presence of enhancing and/or inhibiting factors [2].

What about the time of day? Is there a best time to take magnesium? It’s possible magnesium uptake in the gut may follow a circadian rhythm, but to our knowledge, there is still no clear evidence that the time of day influences magnesium absorption. 

But absorption is just one aspect of magnesium supplementation; retention is also important as magnesium must be retained in the body to exert its functions and provide benefits. How well magnesium is retained depends on its cellular uptake and urinary excretion. Unlike absorption, there is evidence that both cellular uptake and urinary excretion of magnesium are influenced by the time of day. Based on that evidence, earlier in the day may be the best time to take magnesium.* Let’s see why.

Circadian Rhythm of Cellular Magnesium Uptake

In vitro studies in human cells have shown that intracellular magnesium levels follow circadian rhythms associated with the light-dark cycle. During the day, there was a higher inflow of magnesium into cells, leading to an increase in intracellular levels, while at night, there was a higher outflow of magnesium from cells, leading to a decrease in intracellular levels [3]. The oscillations in cellular magnesium levels likely resulted from circadian rhythms in the expression and activity of magnesium channels and transporters in the cellular membrane that influenced the flow of magnesium [1,3,4]. 

Given magnesium’s role as an enzyme cofactor in all major metabolic pathways, in cell energy production, and in ATP activity (ATP is the cell energy molecule) [1], it’s possible that the circadian rhythms of magnesium uptake may serve to adjust cellular energy metabolism and ATP expenditure to the appropriate time of the day. Higher intracellular magnesium levels during the day may facilitate the most energy-consuming activities of human cells (e.g., protein production) when we’re awake and there is fuel intake, while the decline in intracellular magnesium levels at night may promote the conservation of energy when fuel intake pauses [3]. 

Circadian Rhythm of Magnesium Excretion

Studies that have assessed circadian variations of magnesium in plasma have generally shown mixed results and only slight changes that are most likely due to food intake [5–10]. Overall, plasma magnesium levels are generally maintained at stable levels [11]. In healthy conditions, the kidney has the main role in maintaining plasma levels, as they are primarily regulated by magnesium excretion in urine [11–14]. 

Around 95% of plasma magnesium filtered by the kidneys is immediately reabsorbed; only 3–5% is excreted in the urine. However, the kidneys can make considerable adjustments to the rate of magnesium reabsorption and excretion in response to variations in plasma magnesium levels—excretion of filtered plasma magnesium may vary from only 0.5 to up to 70%. This means that the kidney can conserve magnesium when plasma levels are low and quickly eliminate it if plasma levels increase. This happens after magnesium intake: most free magnesium absorbed from the gut that is not taken up by tissues is quickly excreted [11,15,16].

Magnesium excretion by the kidneys follows a circadian rhythm, with maximal excretion occurring at night [11,12,17]. Given how plasma levels remain stable, it’s possible that the higher excretion at night may be associated with the changes observed at the cellular level, i.e., with the increased magnesium outflow at night, but it’s still unclear if these oscillations are directly linked. 

When to Take Magnesium 

What does this all mean regarding the best time of day to take magnesium? 

If cells have a circadian pattern of magnesium uptake, it is possible that the whole organism has one as well. A fraction of magnesium uptake in the gut is done through transporters that may also have circadian regulation, as the ones in cells do. But more research is still needed to elucidate whether that’s the case. Based on what is currently known, here is our best take on the timing of magnesium intake.

Taking in the Morning

In humans, magnesium absorption starts approximately 1h after oral intake, reaches a plateau after 2h to 2.5h, and starts to decline after 4h to 5h. After 6h, magnesium absorption is about 80% complete [2,18]. Taking magnesium in the earlier part of the day allows for this whole process to take place while cellular uptake is higher and kidney excretion is lower. Taking magnesium in the morning or early afternoon may therefore be a good option to support magnesium retention and healthy body magnesium levels.*

Another way to optimize your magnesium intake may be to split your daily intake (e.g., breakfast and lunch) as it may allow your body to potentially absorb a higher percentage of magnesium from your serving. Studies in humans reported higher bioavailability when the same amount of magnesium (from mineral water) was distributed throughout the day rather than being taken in a single serving [19–21].*

The reason is that magnesium absorption does not increase proportionally to magnesium intake but is rather inversely related to the ingested dose: the absorption percentage can be about 65-80% when magnesium intake is very low and decline to 10-20% if intake is very high (it’s about 30-50% for amounts around 350 mg). Still, although the percentage absorbed is lower, the net amount absorbed may be higher with a higher serving [2,20,22,23].* 

Taking in the Evening

Given how intestinal magnesium absorption is balanced against renal magnesium excretion (i.e., higher magnesium absorption results in higher renal excretion) [15,24], it is possible that taking magnesium at a time of day when cellular uptake is lower and excretion is higher may result in poorer retention of magnesium. Therefore, taking magnesium at night or late in the day may not be the best option if the goal is to support body magnesium levels as effectively as possible.* 

Nevertheless, there may be circumstances when taking specific magnesium supplements at night may be worth it. Supplementing magnesium to support sleep is one of these circumstances: taking some magnesium either at dinner up until about an hour or so before bedtime can be a useful timing approach to support healthy sleep. For example, magnesium glycinate (also called bisglycinate) is recommended as one of the more calming forms of magnesium supplements because both magnesium and glycine support relaxation and sleep [25–32]. Magnesium acetyl taurate is another type of magnesium thought of as being more of a calming magnesium.* [Note: Qualia Magnesium+ contains both these forms of magnesium.] 

Taking Before Exercise

Magnesium is important for healthy muscle function and low magnesium levels may result in temporary muscle cramps and twitches. Magnesium also supports the activity of ATP, which powers muscle contraction. Consequently, having healthy muscle magnesium levels is important to support your muscles [1,12,33]. But that doesn’t mean you should take magnesium right before you exercise. Being consistent in your intake of magnesium, especially of forms known to support muscle magnesium levels, is likely more helpful than taking magnesium supplements before exercise.* 

Should Magnesium Be Taken With Food?

One study that assessed the effect of a meal on the bioavailability of magnesium from mineral water found that it was about 14% higher when consumed with a meal rather than alone [34]. This may be because of slower gastrointestinal transit that allows more time for uptake and/or the presence of other food components. It’s unclear if meals have the same effects on the absorption of magnesium from supplements, but based on the available evidence, taking magnesium with a healthy meal may be a good option to enhance its absorption.* 

Magnesium Interactions With Other Supplements

Magnesium and calcium interact extensively in normal human physiology. Magnesium acts as a physiological calcium blocker in several tissues. This is an important role because excess calcium can be detrimental to cells; magnesium’s presence helps to maintain calcium levels and activity in balance [35].* 

The dietary intake of each mineral can influence the physiological balance of the other: high supplemental levels of either one may be detrimental when the dietary intake of the other is too low [36]. So, if you’re supplementing magnesium, make sure you have healthy calcium levels in your diet.* 

However, this doesn’t mean you should take magnesium and calcium together. In fact, how calcium may influence magnesium absorption and retention in humans is still poorly understood, but calcium was shown to reduce magnesium absorption in rats [37]. Therefore, if you take both magnesium and calcium supplements, it may be a good option to take them at different times of the day.*

Vitamin D3, on the other hand, may stimulate intestinal magnesium absorption, as several studies have indicated [38,39]. However, studies have also shown higher magnesium excretion in urine when taken with vitamin D3, meaning that the higher absorption may not result in higher retention of magnesium [37,39].* 

Types of Magnesium

There are several forms of magnesium available as supplements that can differ in important aspects, including how well they are absorbed and retained in the body and distributed to tissues, for example. The two main types of magnesium supplements are magnesium chelates (such as magnesium bisglycinate and magnesium creatine chelate) and magnesium salts (such as magnesium citrate and magnesium hydroxide). You can learn more about the different types of magnesium in our article “Which Magnesium Is Best?”.*

Benefits of Magnesium Supplements

Magnesium is crucial for cell function and has numerous benefits to human health. Magnesium supports metabolic health, healthy brain function, mental well-being and stress management, sleep, bone health, cardiovascular health, and gut health, just to name a few. You can learn more about the main benefits of magnesium in our article “Why Do We Need Magnesium?”.

Magnesium’s central role in human health and longevity is why we developed QUALIA MAGNESIUM+, a blend of 9 types of magnesium plus 70 minerals and trace minerals to enhance magnesium absorption and tissue retention.* You can learn more about each form of magnesium, why we chose them, and their properties and benefits in our article “Qualia Magnesium+ Ingredients.”* 

*These statements have not been evaluated by the Food and Drug Administration.  This product is not intended to diagnose, treat, cure, or prevent any disease.

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