Which form of magnesium is best to take?
Magnesium citrate has the strongest evidence for absorption into the body. Magnesium oxide, the cheapest option, demonstrably performs the worst and is best avoided.
Magnesium citrate has the strongest evidence for absorption into the body among the commonly used forms. In a randomised study of 46 healthy adults, citrate produced the highest magnesium levels in blood and saliva after 60 days, compared with magnesium oxide and amino acid chelate. In that study, oxide did not even differ significantly from placebo.
Organic forms of magnesium in general, meaning salts such as citrate, lactate and gluconate, are better absorbed than inorganic forms such as oxide and carbonate. This was shown by 14 studies combined, and the pattern also holds at higher doses: the more you take, the smaller the percentage your body absorbs. Magnesium oxide, the cheapest and most common form found in off-the-shelf supplements, therefore consistently scores the worst.
One notable finding: a single manufacturer-funded study found that a micro-encapsulated form of magnesium maintained a sustained plasma level over six hours. That same study found that magnesium bisglycinate produced no significant rise in plasma magnesium levels, which is striking because that form is often marketed as 'highly absorbable'. Bisglycinate shows such contradictory results across studies that no firm conclusion can be drawn from them.
There are also large differences between commercial products that share the same base form. Research involving thirty participants showed that absorption can vary widely between products, even when they contain the same salt form. The solubility of a product turned out to be a good predictor of actual absorption.
If you want to try magnesium, citrate is the best-supported choice for bioavailability, at a dose of around 300 mg of elemental magnesium per day for at least 60 days in order to achieve a stable effect on your serum levels. Check the label for the amount of elemental magnesium, not the total weight of the salt. If you are taking it specifically for sleep, blood pressure, cramps or another complaint, the choice of form matters less than the question of whether magnesium actually works for that purpose at all.
This answer is based on two randomised studies, a systematic review of 14 studies, and a smaller comparative study of 30 participants. The evidence for magnesium citrate as the best-absorbed standard form is reasonably consistent. The study on micro-encapsulated magnesium was funded by the manufacturer of that product, which makes the results less independent. The finding regarding bisglycinate contradicts existing assumptions but comes from a single study. Across the literature as a whole, results for bisglycinate are contradictory.
Can you take too much magnesium?
Yes, too much magnesium can be dangerous, although serious toxicity through ordinary supplements is rare in people with healthy kidneys. With kidney problems or the use of intravenous magnesium, medical supervision is genuinely necessary.
Which form of zinc is best to take?
Zinc picolinate and zinc histidine have the strongest independent evidence for good absorption, but all comparative studies are small. Avoid large portions of grains around the time of intake, as phytate substantially blocks absorption.
Which form of vitamin B12 is best to take?
The form of vitamin B12 matters less than the dose: when correcting a deficiency, what counts above all is taking enough. When there is an absorption disorder, injections are the indicated route; discuss that with your doctor.
Why does magnesium work for some people but not others?
Whether magnesium works for you depends strongly on which form you take and how high your dose is. Preferably choose an organic form such as citrate rather than oxide, and give it at least two months.
How much magnesium do you need per day?
Research suggests that your body reaches balance at around 165 mg per day, but official recommendations are higher and there is considerable individual variation. In any case, make sure you get enough magnesium-rich foods, as a large part of the population falls short.
Is it better to take magnesium in the evening?
Evening intake sounds logical given magnesium's role in melatonin and sleep, but no research directly compares evening versus morning use. Take magnesium at the time that is easiest for you to stick to consistently, preferably with a meal to limit stomach complaints.