Magnesium after 40: what changes and what to do about it
Magnesium is one of the minerals people most often fall short of, and after 40 the gap tends to widen. Our editorial team explains why, how much you need according to UK and EU guidance, and when a supplement is likely to help.
Why magnesium becomes a bigger issue after 40
Magnesium is involved in more than 300 enzymatic reactions, from energy production and protein synthesis to nerve conduction, muscle contraction and the regulation of blood glucose. Roughly half of the body's store sits in bone, most of the rest inside muscle and soft tissue, and less than one per cent circulates in the blood.
From the fourth decade onwards several factors start to work against magnesium status at the same time. Absorption from the gut tends to decline with age, kidney handling changes, and the use of medicines that increase magnesium losses becomes more common. Dietary intake also often falls as appetite and overall food volume decrease.
For people who stay active after 40, there is an additional factor: sweat losses and higher energy turnover. Endurance runners, cyclists and those who train in hot conditions lose some magnesium in sweat, and heavy training increases the demand for the mineral in muscle metabolism.
The challenge is that a standard serum magnesium test reflects only a tiny fraction of total body stores. A normal result does not rule out a subclinical shortfall, which is why reviews such as that by Rosanoff and colleagues argue that suboptimal magnesium status is likely underestimated.
How much magnesium adults need in the UK
UK reference nutrient intakes, set by the Department of Health in 1991 and still used today, are 300 mg per day for men and 270 mg per day for women. The European Food Safety Authority set adequate intakes of 350 mg for men and 300 mg for women in 2015. These figures do not change after 40, but meeting them becomes harder for the reasons described above.
National Diet and Nutrition Survey data have repeatedly shown that a proportion of adults in Britain fall below the lower reference nutrient intake, particularly women and older adults. Diets high in refined grains and low in vegetables, pulses, nuts and wholegrains are the main reason.
| Food (typical portion) | Approximate magnesium |
|---|---|
| Pumpkin seeds, 30 g | around 150 mg |
| Almonds, 30 g | around 75 mg |
| Cooked spinach, 90 g | around 70 mg |
| Wholemeal bread, 2 slices | around 50 mg |
| Cooked black beans, 80 g | around 50 mg |
| Dark chocolate (70%+), 20 g | around 45 mg |
Values are approximate and vary by product and cooking method, but they show that a diet built around minimally processed plant foods can meet requirements without supplements. The difficulty is that many busy adults do not eat this way consistently.
For supplements, the UK Expert Group on Vitamins and Minerals set a guidance level of 400 mg per day of supplemental magnesium, above which diarrhoea becomes more likely. EFSA's tolerable upper level for supplemental magnesium is lower, at 250 mg per day. These limits apply to supplements and fortified foods, not to magnesium naturally present in food.
Muscle, sleep, blood pressure and bones
The research on magnesium for active people over 40 is mixed but interesting. Veronese and colleagues found that older women taking 300 mg of magnesium daily for twelve weeks alongside an exercise programme improved some measures of physical performance, such as chair-stand time and gait speed, compared with placebo. The effect was most noticeable in those with lower baseline intake.
A review by Zhang and co-workers concluded that supplementation may help exercise performance mainly in people who are deficient, while benefits in well-nourished athletes are inconsistent. This pattern – benefit when correcting a shortfall, little beyond that – is common to many micronutrients.
Blood pressure is another area of interest after 40. A meta-analysis by Kass and colleagues found small but statistically significant reductions in systolic and diastolic pressure with magnesium supplementation. The effect is modest and does not replace medication, but it fits with the mineral's role in vascular tone.
For bone health, magnesium works alongside calcium and vitamin D. It is required for the activation of vitamin D and for normal parathyroid hormone function, which becomes relevant for women around and after the menopause. Evidence for magnesium alone preventing fractures is limited, but adequate intake is part of a sensible bone-health strategy.
Choosing a form and using it sensibly
Magnesium supplements come in many forms. The main practical differences are the amount of elemental magnesium per tablet, gastrointestinal tolerance and cost. Organic salts such as citrate, glycinate (bisglycinate) and lactate tend to be absorbed somewhat better than magnesium oxide, which nevertheless delivers a lot of magnesium per tablet.
- Citrate: well absorbed, inexpensive, may loosen stools at higher amounts.
- Glycinate/bisglycinate: usually gentle on the stomach, often chosen for evening use.
- Oxide: high magnesium content, lower absorption, more laxative effect.
- Malate, taurate, threonate: marketed for specific benefits that are not yet well supported in humans.
A practical approach for a healthy adult is to assess diet first, then, if a supplement seems sensible, choose a product providing 150–300 mg of elemental magnesium per day, taken with food. Splitting the amount between two meals can improve tolerance. Many people take it in the evening, though timing matters less than consistency.
Read labels carefully. A tablet that lists "magnesium citrate 1000 mg" does not contain 1000 mg of magnesium; the elemental content will be much lower. Combined products with zinc and vitamin B6 (often sold as "ZMA") should be checked against upper limits for each component.
Who should be cautious
People with reduced kidney function should not take magnesium supplements without medical advice, because impaired excretion can lead to accumulation. Kidney function declines with age, and many people over 40 have mild chronic kidney disease without realising it.
Magnesium can interact with several common medicines. It reduces the absorption of tetracycline and quinolone antibiotics, bisphosphonates used for osteoporosis and levothyroxine, so these should be separated by several hours. Long-term proton pump inhibitors, some diuretics and certain diabetes medications may lower magnesium levels, which is worth discussing at medication reviews.
Symptoms such as persistent muscle cramps, palpitations, fatigue or tingling should be assessed by a doctor rather than self-treated. They may relate to magnesium, but also to other electrolytes, thyroid function, iron status or heart rhythm.
Editorial team's conclusions
After 40, magnesium status is influenced by declining absorption, medication use, changes in diet and – for active people – training losses. Many adults in the UK do not meet reference intakes.
The first step is food: seeds, nuts, pulses, wholegrains and leafy greens. Supplements make most sense where dietary intake is low or needs are higher, and the evidence suggests that benefits are mainly seen when correcting a shortfall.
Choose a well-absorbed form, keep supplemental intake within UK and EU guidance, and pay attention to kidney function and medication interactions.
If this topic is relevant to you, you may also find our articles on vitamin D for active adults, on electrolytes for endurance training and on protein needs after 40 useful.
References
- de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev. 2015;95(1):1–46.
- Rosanoff A, Weaver CM, Rude RK. Suboptimal magnesium status in the United States: are the health consequences underestimated? Nutr Rev. 2012;70(3):153–164.
- Veronese N, Berton L, Carraro S, et al. Effect of oral magnesium supplementation on physical performance in healthy elderly women involved in a weekly exercise program: a randomized controlled trial. Am J Clin Nutr. 2014;100(3):974–981.
- Zhang Y, Xun P, Wang R, et al. Can magnesium enhance exercise performance? Nutrients. 2017;9(9):946.
- Kass L, Weekes J, Carpenter L. Effect of magnesium supplementation on blood pressure: a meta-analysis. Eur J Clin Nutr. 2012;66(4):411–418.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for magnesium. EFSA J. 2015;13(7):4186.
- Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals. London: Food Standards Agency; 2003.
