Magnesium and bone health have a closer relationship than most people realise — and one that is more mechanistically fundamental than the nutrient’s low profile in public health messaging suggests. Calcium receives nearly all the attention in bone health messaging, while magnesium — the fourth most abundant mineral in the body and the second most abundant intracellular cation — plays a quieter but equally essential structural and regulatory role. Approximately 60% of total body magnesium is stored in bone; of that skeletal magnesium, roughly half is incorporated into the hydroxyapatite crystal lattice as a structural component, and half is adsorbed on the bone surface as a reservoir that buffers blood magnesium levels. Low magnesium intake is common in Western populations — UK dietary surveys suggest that up to 70% of adults consume less magnesium than recommended — and the evidence linking magnesium insufficiency to lower bone density and higher fracture risk has strengthened considerably over the past decade.
What Magnesium Does in Bone
Magnesium contributes to bone health through several interconnected mechanisms that extend well beyond its structural presence in hydroxyapatite:
Hydroxyapatite crystal size and stability. Magnesium ions substitute for calcium ions at certain sites in the hydroxyapatite lattice, modulating crystal size and perfection. Smaller, more imperfect crystals — the result of adequate magnesium — are paradoxically more resistant to fracture than the larger, more perfect crystals formed in low-magnesium states. This is because smaller crystals accommodate stress better through controlled micro-deformation. Magnesium deficiency produces larger, more brittle hydroxyapatite crystals that fracture more readily under impact load.
Parathyroid hormone (PTH) regulation. Magnesium is required for both the secretion and peripheral action of PTH. Severe magnesium deficiency (hypomagnesaemia) causes a paradoxical PTH deficiency — magnesium depletion impairs PTH release from the parathyroid glands even when calcium is low, and also blunts the kidney’s response to PTH at its receptor. This produces hypocalcaemia that is resistant to calcium and vitamin D supplementation until magnesium is repleted — a clinically important scenario in hospital settings where hypocalcaemia that fails to correct with calcium infusion often indicates underlying hypomagnesaemia. Even moderate magnesium insufficiency affects PTH dynamics, with consequences for calcium-phosphate-PTH balance and bone remodelling regulation over the long term.
Vitamin D activation. Magnesium is a cofactor for the hepatic enzyme (25-hydroxylase) that converts vitamin D to its storage form (25-OHD), and for the renal enzyme (1α-hydroxylase) that converts 25-OHD to active calcitriol. Magnesium deficiency reduces vitamin D activation even when vitamin D intake is adequate — a frequently overlooked interaction that may explain why some individuals appear to respond poorly to vitamin D supplementation. Studies show that vitamin D supplementation in magnesium-deficient individuals produces a blunted 25-OHD rise until magnesium status is corrected.
Osteoblast and osteoclast function. Magnesium is required for more than 300 enzymatic reactions, including ATP-dependent processes essential to both osteoblast (bone-forming) and osteoclast (bone-resorbing) activity. Low magnesium selectively suppresses osteoblast function while increasing osteoclast activity, shifting the remodelling balance toward net resorption — in the same direction as, and compounding the effect of, oestrogen deficiency in postmenopausal women.
Magnesium and Bone Density: Evidence
Population studies consistently show a positive association between magnesium intake and bone mineral density. The Framingham Osteoporosis Study found that higher magnesium intake was associated with significantly greater BMD at the hip and lumbar spine in both men and women, with a dose-response relationship. A large Norwegian cohort study (NOREPOS) found magnesium intake was inversely associated with hip fracture risk, independent of calcium and vitamin D intake.
Intervention studies are more limited but generally supportive. A randomised trial in postmenopausal women given magnesium supplementation (250–750 mg/day) over two years showed attenuation of the age-related bone loss seen in the placebo group. The effect size is smaller than that of pharmacological agents but is clinically meaningful given magnesium’s role in enabling vitamin D activation — correcting magnesium insufficiency may potentiate the bone-protective effects of vitamin D supplementation already in place.
Serum magnesium is a poor marker of total body magnesium status because serum levels are maintained at the expense of bone and intracellular reserves. A low serum magnesium (below 0.75 mmol/L) indicates significant depletion, but normal serum magnesium does not exclude tissue insufficiency. This makes dietary assessment more clinically useful than blood testing for most adults.
Dietary Sources and Requirements
The UK reference nutrient intake (RNI) for magnesium is 300 mg/day for adult men and 270 mg/day for adult women. These are the minimum targets; some researchers suggest that optimal bone health may require intakes closer to 350–400 mg/day, particularly in older adults with reduced gut absorption efficiency.
The best dietary sources of magnesium are:
- Pumpkin seeds (30 g): approximately 160 mg magnesium — among the richest sources per gram
- Dark chocolate (30 g, 70%+ cocoa): approximately 65 mg magnesium
- Almonds (30 g): approximately 80 mg magnesium
- Cashews (30 g): approximately 75 mg magnesium
- Cooked black beans (100 g): approximately 70 mg magnesium
- Cooked spinach (100 g): approximately 85 mg magnesium — one of the best vegetable sources
- Wholemeal bread (2 slices): approximately 40 mg magnesium
- Cooked quinoa (100 g): approximately 64 mg magnesium
- Edamame (100 g cooked): approximately 65 mg magnesium
- Mackerel or salmon (100 g): approximately 35 mg magnesium
A practical diet achieving 300 mg/day might include: a handful of almonds or pumpkin seeds (80 mg), a portion of legumes or edamame at one meal (65 mg), two slices of wholemeal bread (40 mg), a portion of leafy greens (40 mg), and contributions from wholegrains, fish, and other vegetables throughout the day. This is achievable for most adults eating a varied diet — but is easily undercut by diets high in refined grains, ultra-processed foods (which contain negligible magnesium), and low in nuts, seeds, and legumes.
An important practical consideration is cooking method. Boiling vegetables in water leaches water-soluble minerals including magnesium into the cooking water; steaming, roasting, or stir-frying vegetables retains more magnesium than boiling. For legumes and grains, soaking before cooking and discarding the soaking water reduces phytic acid (which can bind magnesium and reduce absorption), potentially improving the net magnesium available from these foods. Fermented grain products — sourdough bread, fermented porridges — similarly have reduced phytate content compared with their unfermented equivalents. These preparation-level considerations can meaningfully improve the bioavailable magnesium from a diet that is already rich in whole-food sources, without requiring any increase in total food intake.
Conditions That Cause Magnesium Deficiency
Several medical conditions and medications reduce magnesium status, making bone health worse in already-vulnerable populations:
- Type 2 diabetes and insulin resistance — hyperglycaemia causes urinary magnesium wasting; insulin resistance impairs cellular magnesium uptake; magnesium deficiency is found in 25–38% of type 2 diabetic patients and is associated with worse glycaemic control and lower bone density
- Proton pump inhibitors (PPIs) — long-term PPI use (typically above 12 months) causes hypomagnesaemia in a clinically significant proportion of patients by reducing intestinal magnesium absorption; this is a recognised, box-labelled side effect of PPIs
- Diuretics — loop diuretics (furosemide) and thiazides increase urinary magnesium excretion; patients on long-term diuretics for heart failure or hypertension are at elevated risk of magnesium depletion
- Coeliac disease and Crohn’s disease — intestinal malabsorption impairs magnesium absorption alongside calcium and vitamin D; untreated coeliac disease is associated with magnesium depletion as well as the more commonly discussed calcium and vitamin D issues
- Chronic alcohol use — alcohol increases urinary magnesium excretion and reduces dietary intake; heavy alcohol use is associated with hypomagnesaemia and accelerated bone loss
- Older age — intestinal magnesium absorption efficiency declines with age; older adults are among those most likely to have dietary magnesium below the RNI
Supplementation Considerations
Magnesium supplementation is appropriate when dietary intake is consistently below the RNI and cannot be corrected through diet, or when a clinical condition (PPI use, diabetes, malabsorption) is causing depletion. There is no established pharmacological indication for magnesium supplementation specifically in osteoporosis management in the way there is for calcium and vitamin D, but addressing magnesium insufficiency is important as part of the nutritional foundation for bone health — particularly because magnesium deficiency may blunt the response to vitamin D supplementation.
Common forms of magnesium supplement and their properties:
- Magnesium citrate — well-absorbed, widely available, gentle on the gut at standard doses; recommended for most people
- Magnesium glycinate — highly bioavailable, least likely to cause laxative effects; preferred for those who experience GI side effects with other forms
- Magnesium oxide — high elemental magnesium content but low bioavailability (approximately 4%); acts primarily as an osmotic laxative; not recommended for bone health supplementation
- Magnesium malate — reasonable bioavailability; often better tolerated than oxide
Typical supplemental doses for bone health support are 200–400 mg/day of elemental magnesium. Upper safe limit for supplemental magnesium is generally considered to be 350 mg/day in adults (UK safe upper level); dietary magnesium from food does not carry the same risk as supraphysiological supplement doses. The most common side effect of excess magnesium supplementation is diarrhoea (the osmotic laxative effect), which typically resolves on dose reduction.
Magnesium and Type 2 Diabetes: A Bone Health Connection
The relationship between magnesium, type 2 diabetes, and bone health illustrates how metabolic conditions can compound skeletal risk through nutritional depletion. Type 2 diabetes is itself associated with an increased fracture risk — paradoxically, even in individuals with normal or above-normal bone mineral density (because diabetes impairs bone quality through advanced glycation end-products that cross-link collagen and reduce its mechanical resilience). Magnesium deficiency adds a further layer to this already complex picture.
In type 2 diabetes, chronic hyperglycaemia drives osmotic diuresis — excess glucose in the urine pulls water and electrolytes, including magnesium, into the urinary tract. The result is ongoing urinary magnesium wasting, which depletes body magnesium stores even when dietary intake is adequate. Studies have found serum magnesium below the reference range in 25–38% of people with type 2 diabetes, and lower serum magnesium in diabetic individuals correlates with worse glycaemic control (partly because magnesium is a cofactor for insulin receptor signalling), greater cardiovascular risk, and lower bone density.
For people with type 2 diabetes and bone health concerns, ensuring adequate dietary magnesium — and considering supplementation if dietary intake cannot meet the RNI — is a clinically relevant step. Metformin, the first-line medication for type 2 diabetes, does not cause magnesium depletion; however, the glycaemic control it provides may reduce the urinary magnesium loss driven by hyperglycaemia, making it indirectly beneficial for magnesium status. Individuals on insulin or sulphonylureas who achieve tight glycaemic control may similarly see improvement in magnesium retention over time.
Magnesium, Calcium, and Vitamin D: The Interdependency
Magnesium does not work in isolation from calcium and vitamin D — the three are closely interdependent in bone health. Adequate magnesium is required for vitamin D to be activated (see our guide to vitamin D and bone health); without it, vitamin D supplementation has a blunted effect. Adequate vitamin D is required for efficient calcium absorption (see our guide to calcium and bone health); without it, dietary calcium is poorly absorbed regardless of intake. And adequate calcium is the structural material that both magnesium and vitamin D ultimately support.
In practice, the interdependency means that optimising all three simultaneously produces better bone outcomes than optimising any one in isolation. A person with high calcium intake but low magnesium and vitamin D may have suboptimal vitamin D activation and therefore suboptimal calcium absorption — achieving less bone protection than expected from calcium intake alone. Addressing the triad (calcium from diet, vitamin D from supplementation and sunlight, magnesium from diet or supplementation as needed) provides the most complete nutritional foundation for bone health alongside exercise and, where clinically indicated, pharmacological treatment. Full context on osteoporosis management and risk assessment is in our guides to osteoporosis: symptoms, causes, and prevention and osteoporosis risk factors.
Frequently Asked Questions
Is magnesium important for bone health?
Yes — approximately 60% of total body magnesium is stored in bone, where it has both structural and regulatory roles. Structurally, magnesium is incorporated into the hydroxyapatite crystal lattice, where it modulates crystal size in a way that improves fracture resistance. Functionally, it is required for PTH secretion and action, vitamin D activation (as a cofactor for both conversion steps), and osteoblast activity. Low magnesium intake is associated with lower bone mineral density and higher fracture risk in population studies. Despite this, magnesium receives far less attention than calcium and vitamin D in mainstream bone health messaging.
What are the best food sources of magnesium?
The richest magnesium sources are nuts and seeds (particularly pumpkin seeds, almonds, cashews), legumes (black beans, edamame, lentils), dark leafy greens (spinach, kale), wholegrains (brown rice, wholemeal bread, quinoa), dark chocolate (70%+ cocoa), and oily fish. These are the food categories most consistently associated with higher magnesium status in dietary surveys. Ultra-processed foods — refined grains, packaged snacks, fast food — are very low in magnesium, and a diet dominated by them is likely to be deficient in magnesium even at adequate caloric intake.
Can magnesium deficiency cause low vitamin D?
Not directly — magnesium deficiency does not reduce vitamin D production from sunlight or reduce dietary vitamin D intake. However, magnesium is a required cofactor for the enzymes that activate vitamin D in the liver (to 25-OHD) and the kidney (to calcitriol). In magnesium-deficient individuals, these activation steps are impaired, and the circulating level of active calcitriol may be lower than expected given the vitamin D intake. Studies have shown that supplementing with vitamin D in magnesium-deficient individuals produces a blunted rise in 25-OHD compared with magnesium-replete individuals. Correcting magnesium deficiency alongside vitamin D supplementation produces better outcomes than vitamin D alone in these cases. This interaction is one reason bone health recommendations increasingly mention magnesium alongside calcium and vitamin D rather than treating them as independent nutrients.
Should I take a magnesium supplement for bone health?
If your dietary magnesium consistently meets the RNI (300 mg/day for men, 270 mg/day for women) from a varied diet including nuts, seeds, legumes, and wholegrains, supplementation is generally not necessary for bone health purposes. Supplementation is appropriate if diet alone cannot achieve the RNI (for example, in individuals with restricted diets, malabsorption conditions, or medications causing magnesium loss such as PPIs or loop diuretics), or if you are taking vitamin D supplements and want to ensure your magnesium status is not limiting vitamin D activation. When supplementing, magnesium citrate or glycinate are better absorbed and better tolerated than oxide, which acts primarily as a laxative. Doses of 200–350 mg/day elemental magnesium are appropriate for most adults.
Do PPIs affect magnesium and bone health?
Yes — long-term use of proton pump inhibitors (PPIs such as omeprazole, lansoprazole, pantoprazole) is associated with hypomagnesaemia in a clinically significant proportion of patients and also with modestly increased fracture risk. The fracture risk from PPIs is multi-factorial: impaired calcium absorption (PPIs reduce gastric acid needed to dissolve calcium carbonate), reduced magnesium absorption (PPI-induced hypomagnesaemia), and possible direct effects on osteoclast activity. People on long-term PPI therapy (above 12 months) with bone health concerns should discuss their PPI use with their GP — in some cases reviewing whether the PPI indication remains necessary, and considering monitoring of magnesium and bone density if additional risk factors are present.
How much magnesium is too much?
Dietary magnesium from food is safe at any level achievable through diet because the kidneys efficiently excrete excess magnesium. Supplemental magnesium at doses above 350 mg/day carries a risk of osmotic diarrhoea and GI discomfort. The European Food Safety Authority sets the tolerable upper level for supplemental magnesium at 250 mg/day for adults; the UK safe upper level is 350 mg/day. Very high supplemental doses (above 1,000 mg/day) in individuals with impaired renal function can cause hypermagnesaemia, which is clinically dangerous (cardiac arrhythmia, respiratory depression). For healthy adults, staying within 350 mg/day of supplemental magnesium, in addition to dietary magnesium, is safe for long-term use.
Is magnesium deficiency common in the UK?
Insufficient magnesium intake (below the RNI) is very common in the UK — dietary surveys suggest up to 70% of adults consume less than the recommended amount, with teenage girls, older adults, and people with diets high in ultra-processed foods at greatest risk. Frank hypomagnesaemia (low serum magnesium) is less common in the general population but is frequently present in people with type 2 diabetes, those on long-term PPIs or loop diuretics, and those with malabsorption conditions. Because serum magnesium is maintained at the expense of bone and intracellular stores, low serum magnesium indicates significant whole-body depletion, but normal serum magnesium does not confirm adequacy at the tissue level.
Summary
Magnesium is a structurally and functionally essential mineral for bone health, contributing to hydroxyapatite crystal size and fracture resistance, vitamin D activation, PTH secretion and receptor action, and osteoblast function — four distinct mechanisms that collectively make magnesium insufficiency a meaningful contributor to bone loss and fracture risk. Approximately 60% of body magnesium is stored in bone — half as a structural lattice component in hydroxyapatite, half as a surface reservoir that buffers blood magnesium — making it a direct participant in skeletal composition as well as a regulator of the hormonal and enzymatic pathways that govern bone remodelling. Dietary insufficiency is common, particularly in Western diets high in ultra-processed foods and low in nuts, seeds, legumes, and whole grains. Certain conditions and medications (type 2 diabetes, PPIs, loop diuretics, coeliac disease) cause magnesium depletion and compound bone loss risk. Addressing magnesium status — through diet and supplementation where needed — is an important complement to calcium and vitamin D in a complete bone health strategy. The interaction with type 2 diabetes — where hyperglycaemia drives ongoing urinary magnesium wasting and compounds skeletal risk — makes magnesium status particularly relevant for the large and growing population of adults managing both metabolic and bone health conditions simultaneously. For full context on bone health across the life course, see our guides to bone density: what it means and DEXA scan: what adults should know. For the bone health measures used in clinical assessment, our guide to the bone density test explains what a DEXA result means in practice, and how nutritional interventions like magnesium, calcium, and vitamin D adequacy feed into the overall clinical picture.
Medical disclaimer: This article is for general educational purposes and does not constitute medical advice. Consult a qualified healthcare professional for personalised nutrition and bone health advice.
References:
Castiglioni S, et al. Magnesium and osteoporosis: current state of knowledge and future research directions. Nutrients. 2013;5(8):3022–3033.
Rondanelli M, et al. An update on magnesium and bone health. BioMetals. 2021;34(4):715–736.
NHS. Other vitamins and minerals. nhs.uk. 2023.
Royal Osteoporosis Society. Nutrition for bones. theros.org.uk. 2023.
I’ve been on omeprazole 40 mg daily for seven years for reflux, and was recently diagnosed with osteoporosis (T-score −2.7 at the spine) after a vertebral fracture. When my GP reviewed my medications she specifically mentioned that long-term PPI use was a contributing factor to my bone loss — both through reduced calcium absorption (PPIs reduce the stomach acid needed to dissolve calcium carbonate) and through hypomagnesaemia. A blood test confirmed my magnesium was low at 0.62 mmol/L. I was switched to the lowest effective omeprazole dose and referred to a gastroenterologist to review whether I still needed a PPI at all. I was also started on alendronate, calcium citrate (not carbonate, because of the PPI), and a magnesium citrate supplement. My magnesium normalised within six weeks of supplementation. This article explains the PPI-magnesium-bone connection clearly and is the first public health information I’ve found that addresses all three parts of this simultaneously.
Judith, your case illustrates the PPI-magnesium-bone triad that is increasingly recognised but still inconsistently managed. The dual mechanism of PPI impact on bone — reduced calcium carbonate absorption (from decreased gastric acid) and hypomagnesaemia (from impaired intestinal magnesium absorption) — explains why your bone loss was more severe than would be expected from oestrogen deficiency alone. The switch to calcium citrate is exactly correct in your situation: citrate dissolves independently of stomach acid and is absorbed effectively even with PPI-suppressed gastric acid secretion, whereas carbonate requires acidic conditions and is poorly dissolved in PPI-treated patients. Magnesium citrate supplementation with normalisation at six weeks is the expected response. The ongoing PPI review is important — many patients on long-term PPIs can step down to H2 blockers or on-demand therapy once the initial indication (often acute reflux or healing) has resolved. Thomas, your GP’s approach reflects current best practice for diabetic bone health assessment: DEXA after a defined duration of disease, combined with metabolic markers including magnesium. The point about serum magnesium representing only extracellular magnesium — and underestimating intracellular and skeletal depletion in diabetic individuals — is clinically important. In people with hyperglycaemia-driven urinary magnesium wasting, normalising glycaemic control reduces ongoing renal losses, and dietary magnesium improvement combined with supplementation (if needed) addresses the tissue deficit. Your FRAX score at these T-scores and your age should determine whether pharmacological treatment is also warranted — a discussion worth having with your GP at the next review.
I have type 2 diabetes (diagnosed eight years ago, now well controlled on metformin) and was referred for a DEXA scan at 59 after my GP flagged that my bone density hadn’t been checked despite my diabetes duration. My T-scores were −1.9 at the spine and −1.5 at the hip — osteopenia at the spine. My GP also checked my serum magnesium, which was 0.71 mmol/L — within the reference range but at the low end. She mentioned that for people with diabetes, even borderline-low magnesium may represent a more significant intracellular deficit than the blood level suggests. I was advised to increase dietary magnesium through more nuts, legumes, and whole grains, and to consider a magnesium citrate supplement if my dietary changes were insufficient. The article’s connection between hyperglycaemia, urinary magnesium wasting, and compound bone health risk in type 2 diabetes explains clearly why my GP was looking at magnesium alongside bone density — I hadn’t understood the connection before.