Jarrow Formulas MagMind Stress Resistance

Magnesium L-threonate (Magtein)· evidence: Limited

Magnesium L-threonate, sold under the trade name Magtein, is magnesium bound to threonic acid. It is marketed for the brain because animal studies suggested it raises magnesium levels in the brain more than other forms. In people, the evidence is a handful of small trials, several funded by the ingredient's maker, so it is far from settled. Claims about memory, focus, brain health or sleep are not authorised.

It is also a low-strength way to get magnesium: 2,000 mg of Magtein provides only about 144 mg of elemental magnesium (38% NRV), at several times the price of citrate or glycinate. If you simply want to top up your magnesium intake, other forms are much better value.

Typical dose: Trials have used about 1.5–2 g of magnesium L-threonate a day, giving roughly 100–144 mg of elemental magnesium.

Safety: Generally well tolerated; some people report headaches or drowsiness. Keep total magnesium from supplements within the EFSA upper level of 250 mg a day unless advised otherwise. Take apart from tetracycline or quinolone antibiotics and bisphosphonates. Speak to your GP first if you have kidney disease.

Research we looked at:
Slutsky I et al. (2010). Enhancement of learning and memory by elevating brain magnesium. Neuron 65(2):165–177.
Liu G et al. (2016). Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults. J Alzheimers Dis 49(4):971–990.
EFSA NDA Panel (2015). Scientific opinion on dietary reference values for magnesium. EFSA Journal 13(7):4186.

L-theanine· evidence: Limited

L-theanine is an amino acid found naturally in tea leaves. Small human studies, usually using 200 to 400 mg a day, have looked at feelings of stress, relaxation and sleep quality, with some positive but inconsistent results.

The studies are mostly small and short, and when EFSA reviewed the evidence in 2011 it did not authorise any health claims for L-theanine. It is generally well tolerated, but there is not enough good evidence to say it reliably makes a difference for healthy people.

Typical dose: 100 to 400 mg a day in studies; 200 mg is common in supplements.

Safety: Generally well tolerated in studies. Not well studied in pregnancy or breastfeeding. Speak to your doctor if you take blood pressure medicines or sedatives.

Research we looked at:
EFSA NDA Panel (2011). Scientific Opinion on the substantiation of health claims related to L-theanine. EFSA Journal 9(6):2238.
Hidese S et al. (2019). Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients 11(10):2362.
Williams JL et al. (2020). The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review. Plant Foods for Human Nutrition 75:12-23.

Rhodiola rosea· evidence: Limited

Rhodiola rosea is a plant root traditionally used in Scandinavia and Russia. Studies have looked at mental and physical tiredness and how people respond to stress, usually with standardised extracts of 200 to 600 mg a day.

Reviews of the trials describe the evidence as limited and the studies as small, short and of mixed quality, with inconsistent results. Botanical health claims are not authorised in the UK, so we describe the research only and make no claims about what it does.

Typical dose: 200 to 600 mg a day of a standardised root extract in studies.

Safety: Can cause dizziness or dry mouth in some people. Not recommended in pregnancy or breastfeeding. Speak to your doctor if you take antidepressants, diabetes or blood pressure medicines, or have bipolar disorder.

Research we looked at:
Ishaque S et al. (2012). Rhodiola rosea for physical and mental fatigue: a systematic review. BMC Complementary and Alternative Medicine 12:70.
Hung SK et al. (2011). The effectiveness and efficacy of Rhodiola rosea L.: a systematic review of randomized clinical trials. Phytomedicine 18(4):235-244.

Magnesium· evidence: Moderate

Magnesium is an essential mineral found in green vegetables, nuts, seeds, wholegrains and beans. UK surveys show that some groups, particularly teenagers and some adults, eat less than the recommended amount. A supplement reliably raises intake, and people with a low intake or a diagnosed deficiency are the ones most likely to notice a difference. Most people eating a varied diet get enough from food.

Labels often show the weight of the whole compound (for example 1,000 mg of magnesium citrate), but only part of that is magnesium itself. What matters is the elemental magnesium per daily dose, compared with the NRV of 375 mg. Organic forms such as citrate, glycinate (bisglycinate), malate and taurate are generally absorbed a little better than oxide in small studies, but differences between them are modest and no form has been shown to be better for any particular use.

Magnesium is widely sold for sleep, stress and cramp. These are not authorised claims. Reviews have found the evidence for sleep is of low quality, and a Cochrane review found magnesium is unlikely to prevent ordinary muscle cramps in older adults.

Typical dose: Most supplements give 100–400 mg of elemental magnesium a day (NRV 375 mg). The NHS says adults need about 270–300 mg a day in total, mostly from food.

Safety: High doses loosen stools or cause diarrhoea, especially citrate and oxide. EFSA sets an upper level of 250 mg a day of magnesium from supplements, and the FSA advises that up to 400 mg a day from supplements is unlikely to cause harm. Magnesium can reduce absorption of some antibiotics (tetracyclines, quinolones) and osteoporosis drugs (bisphosphonates), so take them a few hours apart. Speak to your GP first if you have kidney disease.

Research we looked at:
NHS. Vitamins and minerals: others – magnesium. nhs.uk.
EFSA NDA Panel (2015). Scientific opinion on dietary reference values for magnesium. EFSA Journal 13(7):4186.
Expert Group on Vitamins and Minerals (2003). Safe upper levels for vitamins and minerals. Food Standards Agency.
Garrison SR et al. (2020). Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev 9:CD009402.

Cost per daily dose lets you compare packs of different sizes fairly.Worked out from our current prices.