Magnesium citrate, glycinate, malate and oxide are not the same thing; they differ in how well they are absorbed and in their effect on the digestive system. We explain the difference between the compound weight on the label and elemental magnesium, why a supplement may not be working and the interactions with medicines.
You look at the boxes lined up on the pharmacy shelf: citrate, glycinate, malate, oxide, taurate… A friend recommended one for sleep, your trainer another for cramps. You bought one and have been taking it for weeks, but nothing has changed in your sleep, your cramps or your energy. The first question that comes to mind is: “Did I buy the wrong magnesium?”
Possibly. But the problem may lie in the form of magnesium, or just as easily in misreading the label, in the way you take the supplement, or in your complaint having nothing to do with magnesium at all. Let us look at each in turn.
What does magnesium do in the body?
Magnesium is a mineral needed for hundreds of enzymes in the body to work. It plays a part in the relaxation of muscles after they contract, in nerve transmission, in producing energy from food, in bone structure, in regulating heart rhythm and in blood sugar control. Most of the magnesium in the body is found in the bones and inside the muscles; the amount circulating in the blood is a very small part of the total.
Signs of magnesium deficiency and who is at risk
Mild deficiency usually gives no symptoms. When it becomes marked, muscle cramps and twitching, tiredness, loss of appetite, headache, sleep problems, constipation and palpitations may be seen. None of these symptoms is specific to magnesium; the same complaints arise from many other causes.
The risk of deficiency increases in the following situations:
- A diet poor in vegetables, pulses, nuts and whole grains and heavy in packaged products
- Regular alcohol consumption
- Long-term use of medicines that suppress stomach acid, or of diuretics
- Poorly controlled diabetes
- Prolonged diarrhoea and bowel diseases that impair absorption
- Older age
A blood test also gives limited information. Because magnesium in the blood reflects only a small part of the body’s store, the stores may be low even when the result is normal. For this reason the result is interpreted by a doctor together with the complaints, the dietary history and the medicines being taken.
What is the difference between the forms of magnesium?
Magnesium is never found on its own; it is always bound to another substance. What we call the form is that substance, and it mainly determines two things: how much is absorbed and how much it affects the bowels.
- Magnesium oxide: It contains a high proportion of magnesium, but its absorption is low. It softens the stool by drawing water into the bowel; for this reason it is used mostly for constipation. Because the amount absorbed is small, it is not an efficient choice for replenishing stores.
- Magnesium citrate: It is well absorbed. It has the effect of increasing bowel movement; for people prone to constipation this is an advantage, while for those with sensitive bowels it may cause diarrhoea.
- Magnesium glycinate (bisglycinate): It is bound to the amino acid glycine. It is among the forms that upset the stomach and bowels least. For this reason it is often chosen by people who cannot tolerate citrate and for use in the evening.
- Magnesium malate: It is bound to malic acid, which plays a part in energy production. It is generally well tolerated; its use for tiredness and muscle pain is widespread, but the evidence in this area is limited.
- Magnesium taurate and threonate: They are marketed with claims about heart and brain health. Studies in humans are not yet at a level that would confirm these claims.
One point needs to be stated plainly here: sharp distinctions of the kind “this form for sleep, that one for muscles, the other for the brain” are marketing language running ahead of the scientific evidence. The proven differences between the forms have mainly to do with absorption and with how well the digestive system tolerates them. The right form for you is chosen according to your needs, your bowel habits and the medicines you take.
Where to look on the label: compound weight or elemental magnesium?
This is the most common mistake made with supplements. The amount written in large letters on the box is usually the total weight of the compound. For example, you see a high amount of magnesium citrate on the label, but only part of it is magnesium itself; the rest is citrate. The value the body uses, and the one you should compare with the daily requirement, is the amount of elemental magnesium.
This information is usually found in the nutrition table on the back. When comparing two products, look not at the number of capsules or the figure on the front, but at the elemental magnesium you get per serving. How much you should take is for your doctor or dietitian to decide.
Why might magnesium not be working?
- You may not be deficient. In someone whose stores are adequate, a supplement makes no noticeable difference.
- The complaint may have another cause. Cramps are also linked to fluid loss, hard exercise, some medicines and problems with circulation and nerves. Behind tiredness there may be iron or B12 deficiency, a thyroid problem, lack of sleep or an inadequate diet.
- A poorly absorbed form may have been chosen. The oxide form is weak at replenishing stores.
- The elemental amount may be less than you think. Misreading the label is common.
- It may be being taken at the same time as other minerals. High doses of zinc, calcium and iron compete with magnesium for absorption.
- Use may be irregular or too short. Replenishing the stores can take weeks.
- It may be causing diarrhoea. When a supplement passes through the bowel quickly, less of it is absorbed.
When should magnesium be taken, and which medicines does it interact with?
Magnesium upsets the stomach less when taken with food. Dividing the daily amount in two instead of taking it all at once improves both absorption and tolerance. There is no proven clear difference between taking it in the morning or in the evening; the right time is the time at which you can take it regularly.
The real point to watch is interaction with medicines. Magnesium binds some medicines in the bowel and reduces their absorption:
- Some antibiotics
- Thyroid hormone medicines
- Some medicines used to treat osteoporosis
A gap of several hours needs to be left between these medicines and magnesium. In people with kidney failure, magnesium can build up in the body, so supplements should not be used without a doctor’s advice. If you take regular medication, consult your doctor or pharmacist before starting a supplement. For people on thyroid medication, the details are on the nutrition for thyroid conditions page.
Foods rich in magnesium
Before a supplement, it is worth looking at the plate. Foods rich in magnesium include:
- Pumpkin seeds, almonds, cashews, hazelnuts and peanuts
- Spinach, chard and other dark green leafy vegetables
- Dried beans, chickpeas, lentils
- Oats, bulgur and wholegrain bread
- Dark chocolate with a high cocoa content, avocado and banana
Because healthy kidneys pass out excess magnesium from food in the urine, there is no risk of taking in too much through diet. A handful of nuts a day, pulses several times a week and a portion of green leafy vegetables every day go a long way towards meeting most people’s needs.
In brief
- The basic difference between the forms of magnesium is absorption and the effect on the bowels.
- On the label, look at elemental magnesium, not the weight of the compound.
- Not every cramp or spell of tiredness is magnesium deficiency.
- Magnesium reduces the absorption of some medicines; in kidney disease it is not used without consulting a doctor.
- The form and amount of a supplement are chosen according to need and health, not on a recommendation from social media.
Frequently asked questions
Should magnesium be taken in the morning or in the evening?
There is no proven clear difference between the two. Forms that stimulate the bowels may be preferred in the morning and gentler forms in the evening; what matters is regular use.
Can magnesium be taken every day?
If there is a need and your doctor or dietitian considers it appropriate, it is taken regularly for the period set. Unnecessary use in high amounts can lead to diarrhoea and, in people with kidney problems, to serious trouble.
Can magnesium be used in pregnancy?
The doctor decides on every supplement to be used in pregnancy. If you have complaints such as cramps, consult your doctor before starting anything on your own.
