Magnesium has become the internet’s answer to almost everything. Cannot sleep, take magnesium. Anxious, take magnesium. Cramping, constipated, tired, stressed — magnesium.
Then you get to the shop and there are five of them at five different prices, and nobody has explained why. So here is the version I would give a client: what it does, which form to actually buy, what the sleep evidence really shows, and the two situations where it is a genuinely bad idea.
What magnesium does
It is a cofactor in several hundred enzyme reactions, which is the line every label quotes and nobody explains. In practical terms it matters for muscle and nerve function, for how your body handles glucose, for blood pressure regulation, and for bone, where more than half your body’s magnesium is stored.
Adults need roughly 400–420 mg a day if male and 310–320 mg if female. Most people are not dramatically short, but plenty sit at the low end, because the food sources are the ones that get squeezed out of a modern diet.
Are you actually deficient?
Here is the part the supplement aisle never mentions: the blood test for magnesium is close to useless for answering this. Only about 1% of your body’s magnesium is in the blood, and your body defends that number hard — pulling from bone if it has to. A normal serum magnesium does not rule out low stores, and it is not routinely included in a panel anyway.
True deficiency is uncommon in healthy people with working kidneys. It becomes genuinely likely in a few situations worth recognising:
- Long-term proton pump inhibitors — the acidity tablets many people take for years without review. This is a well-documented cause of low magnesium
- Diuretics, commonly prescribed for blood pressure
- Poorly controlled diabetes, which increases urinary losses
- Regular heavy alcohol use
- Chronic diarrhoea or any malabsorption, including coeliac and inflammatory bowel disease
If none of those is you, you are probably not deficient. You may still be under-consuming it, which is a different and more boring problem with a food-shaped answer.
On long-term acidity tablets or a diuretic and wondering what they are quietly depleting? Send me your prescription list and I will tell you what to watch.
What low magnesium actually feels like
Since the blood test is unreliable, the clinical picture matters more than usual. Genuine deficiency tends to show up as a cluster rather than a single symptom:
- Muscle twitching, particularly around the eyelid, and cramps that are not related to training
- Fatigue and weakness that does not track with sleep
- Poor appetite, nausea
- Numbness or tingling
- Abnormal heart rhythm, which is the one that needs a doctor rather than a supplement
- Low potassium or low calcium that will not correct — a classic clue, because magnesium is required for both
That last point is the one clinicians use. If your potassium keeps dropping despite replacement, magnesium is usually the reason, and correcting it fixes both.
What magnesium deficiency does not typically look like: vague tiredness on its own, in someone with normal kidneys, a reasonable diet and no medication on the list above. That presentation is far more often iron, B12, vitamin D or thyroid, all of which are properly testable.
The forms, side by side
| Form | Absorption | Gut effect | Best for |
|---|---|---|---|
| Oxide | Poor, single figures | Strongly laxative | Constipation, not repletion |
| Citrate | Good | Mildly laxative at higher doses | General intake, best value |
| Glycinate / bisglycinate | Good | Gentlest | Sleep, sensitive stomachs |
| Malate | Good | Mild | No specific advantage shown |
| Taurate | Good | Mild | Marketed for the heart, evidence thin |
| L-threonate | Good | Mild | Marketed for the brain, expensive, thin evidence |
| Sulfate (Epsom, bath) | Negligible through skin | N/A | Relaxation, not supplementation |
The forms, honestly
Magnesium oxide. The cheapest, the most common on Indian shelves, and the worst absorbed — single-digit percentages. What does not get absorbed pulls water into the bowel, which is why it works as a laxative and why people report loose stools. If your tablet does not say which form it is, it is almost certainly this.
Magnesium citrate. Well absorbed, inexpensive, mildly laxative at higher doses. A sensible default if you simply want to raise intake.
Magnesium glycinate (bisglycinate). Well absorbed and the gentlest on the gut, because the glycine changes how it is handled. This is the one I would pick if the goal is sleep or if citrate sends you to the bathroom.
Malate, taurate, chloride. All reasonable, all absorbed adequately. The specific claims attached to each — malate for fatigue, taurate for the heart — run ahead of the evidence.
L-threonate. Marketed hard for brain and memory on the basis that it crosses into the central nervous system more readily. The human evidence is thin and the price is not. I would not start here.
Epsom salts in the bath. Pleasant. Not a meaningful way to get magnesium into your body — the transdermal absorption claims are not supported. Have the bath because it is relaxing, not because it is supplementation.
The sleep claim, examined
This deserves a straight answer because it is the reason most people buy it.
The systematic review people cite pooled the randomised trials in older adults with insomnia. It found three trials. A hundred and fifty-one people in total. The pooled result suggested falling asleep somewhat faster, and the authors graded the quality of that evidence as low to very low — their words, not mine. The review has since had a published correction.
So: it might help, on thin evidence, in a population that may not resemble you. That is not nothing, and magnesium glycinate is cheap and safe enough that trying it is reasonable. It is simply not the sleep intervention people think they are buying. If sleep is the actual problem, the things with real evidence behind them are a fixed wake time and getting out of bed when you are not sleeping — neither of which comes in a bottle.
One more thing about the sleep evidence
Worth being precise, because this is where most magnesium is sold. The trials were in older adults with diagnosed insomnia, not in generally healthy people who sleep badly on a Sunday. Extrapolating from one group to the other is exactly the move that turns thin evidence into confident marketing.
If you want to try it, glycinate at bedtime for three or four weeks is a reasonable, cheap experiment with a low downside. Judge it on your own sleep rather than on the label, and if nothing changes, stop — that is a result, not a failure.
And the cramps claim, which is weaker still
A Cochrane review pooled eleven trials and 735 people. Its conclusion was that magnesium is unlikely to provide clinically meaningful prevention of ordinary muscle cramps, at any of the doses studied, largely in older adults.
If you cramp regularly, the more useful suspects are hydration, sodium, how hard you trained, and occasionally a medicine you are on. Not magnesium.
Where to get it from food
| Food | Magnesium per 100 g | Realistic portion |
|---|---|---|
| Pumpkin seeds | ~550 mg | A small handful covers a third of the day |
| Almonds | ~270 mg | 20–25 almonds |
| Cashews | ~290 mg | A small handful |
| Rajma and chana (dry) | ~140–160 mg | A regular katori of cooked dal or rajma |
| Spinach (cooked) | ~80 mg | A serving of palak |
| Dark chocolate (70%+) | ~230 mg | Two squares |
| Bajra and jowar | ~130–170 mg | Two rotis |
A plate built on dal, millet roti, vegetables and a handful of nuts does most of this without a tablet. Refined flour and polished rice are where the magnesium quietly disappears from an Indian diet.
How much, and when
| Situation | Typical supplemental dose | Timing |
|---|---|---|
| General top-up | 200–300 mg elemental, citrate | With a meal, any time |
| Trying it for sleep | 200–400 mg elemental, glycinate | 60–90 minutes before bed |
| On thyroid medication | Same as above | Evening only, at least 4 hours from the thyroid tablet |
| Reduced kidney function | Do not self-supplement | Doctor first |
Read the elemental magnesium figure, not the compound weight. A 500 mg magnesium citrate tablet does not contain 500 mg of magnesium — it contains roughly 80 mg of it, and the label will usually say so in smaller print.
The interactions nobody mentions
This is the pharmacist part, and it is the most practically useful thing in this article.
Magnesium binds to several drugs in the gut and stops them being absorbed properly. The ones that matter most:
- Thyroid medication (levothyroxine). Taking magnesium near your thyroid tablet reduces its absorption, and people spend months wondering why their TSH will not settle. Separate them by at least four hours — thyroid tablet on an empty stomach in the morning, magnesium in the evening
- Certain antibiotics — the quinolones and tetracyclines. Separate by several hours or the antibiotic underperforms
- Bisphosphonates for osteoporosis. Same problem, same solution
- Iron. If you are already fighting to absorb an iron tablet, do not take magnesium alongside it
And the situation where magnesium is genuinely unsafe: reduced kidney function. Magnesium is cleared by the kidneys. If they are not clearing well it accumulates, and high magnesium is a real clinical problem rather than a theoretical one. If you have kidney disease, do not supplement without your doctor.
Food first, as usual
Pumpkin seeds, almonds and cashews, spinach and other dark greens, rajma and chana, whole grains, and dark chocolate. An Indian plate built around dal, vegetables and whole grains rather than refined flour does most of this work on its own.
What I will not tell you
That it will fix your anxiety. The trials are small and inconsistent, and if anxiety is affecting your days that deserves a proper conversation rather than a mineral.
That more is better. Past your needs, the surplus is excreted, and the main thing you buy with a bigger dose is diarrhoea.
That the form does not matter. It is the one place in this aisle where paying slightly more genuinely changes what reaches your bloodstream.
The short version
- Serum magnesium is a poor test — only about 1% of body magnesium sits in blood, and it is tightly defended
- Real deficiency clusters around long-term PPIs, diuretics, poorly controlled diabetes, heavy alcohol use and malabsorption
- Oxide is cheap and barely absorbed; citrate is a good default; glycinate is the gentlest and the one to use for sleep
- The sleep evidence is three trials and 151 people, graded low to very low quality — worth trying, not worth relying on
- Cochrane found magnesium unlikely to prevent ordinary muscle cramps at any dose
- Keep it four hours away from thyroid tablets, iron, quinolone and tetracycline antibiotics, and bisphosphonates
- Do not supplement magnesium if your kidney function is reduced
Before you act on any of this
I am a pharmacist and a nutritionist. I am not your doctor, and this article is general information rather than advice about you specifically. If you have reduced kidney function, heart block, or take regular prescription medicines, check before starting magnesium. Nothing here is a reason to start, stop or change a prescribed medicine — including the acidity tablet or diuretic mentioned above. What this article can do is tell you which questions are worth asking at your next appointment.
Sources
- Magnesium: Fact Sheet for Health Professionals (NIH Office of Dietary Supplements)
- Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis (BMC Complementary Medicine and Therapies, 2021)
- Magnesium for skeletal muscle cramps (Cochrane Database of Systematic Reviews, 2020)
