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  • Vitamin D — The Complete Guide

    Vitamin D — The Complete Guide

    If you live in the UK, there’s a roughly one-in-five chance that your vitamin D level is too low right now — and that probability roughly doubles between October and March. Vitamin D is unusual among nutrients because we get most of it not from food but from sunlight on our skin, and at UK latitudes, the sun is too weak to make any from late autumn to early spring. This is why the NHS now formally recommends that everyone in the UK considers a vitamin D supplement during the winter months.

    This guide covers what vitamin D actually does, how much you need, where to get it, who’s at higher risk of deficiency, and how to choose a sensible supplement if you decide to take one.

    Quick disclaimer: Information here is for general guidance and is not medical advice. If you suspect a deficiency, take medication, are pregnant or breastfeeding, or have a health condition such as kidney or liver disease, please speak to your GP before starting a vitamin D supplement at any dose above 10 micrograms (400 IU) per day.

    What vitamin D actually is

    Despite the name, vitamin D is technically a hormone rather than a vitamin. Your skin makes it when UVB rays from the sun convert a cholesterol compound into vitamin D3 (cholecalciferol), which is then processed by your liver and kidneys into the active form that your body uses. The fact that we can make it ourselves — given enough sunlight — is why it slipped into the “vitamin” category historically rather than the “hormone” one.

    Two forms appear on supplement labels:

    • Vitamin D3 (cholecalciferol) — the form made by your skin and the form found in animal foods. This is the form most studies use and most experts recommend for supplementation.
    • Vitamin D2 (ergocalciferol) — the form made by some plants and fungi exposed to UV. It’s vegan but generally less effective at raising blood vitamin D levels than D3.

    If you’re choosing a supplement, D3 is the better default for most people. Vegan D3 is now available, made from lichen rather than lanolin (sheep wool oil).

    What it does in the body

    The European Food Safety Authority (EFSA) has authorised the following health claims for vitamin D:

    • Vitamin D contributes to the normal function of the immune system
    • Vitamin D contributes to the maintenance of normal bones and teeth
    • Vitamin D contributes to the maintenance of normal muscle function
    • Vitamin D contributes to the normal absorption and use of calcium and phosphorus
    • Vitamin D contributes to normal blood calcium levels
    • Vitamin D has a role in the process of cell division

    That EFSA list is the regulatory standard for what we’re allowed to say vitamin D does. Beyond those authorised claims, there’s a wide and active research literature on possible roles in mood, autoimmune conditions, cardiovascular health, and infection risk. Some of that research is promising; some is mixed or has produced conflicting trial results. We summarise the state of evidence below for the most-asked-about areas.

    Bone health (well-established)

    Vitamin D’s most thoroughly proven role is helping your body absorb calcium from food. Without enough vitamin D, even a calcium-rich diet won’t deliver enough calcium to your bones — which over time can lead to softer bones (rickets in children, osteomalacia in adults) and increased fracture risk in older adults. This is the original reason vitamin D fortification was added to UK margarine in the 1940s.

    Immune function (well-established for some outcomes, mixed for others)

    Vitamin D receptors are present on most immune cells, and observational studies consistently find associations between low vitamin D status and increased rates of respiratory infections. Randomised controlled trials of vitamin D supplementation for reducing respiratory infections have produced mixed but generally modest positive results — a Cochrane review concluded vitamin D supplementation produces a small reduction in acute respiratory infection risk in deficient people. For people who already have adequate vitamin D, the additional benefit is less clear.

    Muscle function and falls in older adults (reasonable evidence)

    Several studies have linked low vitamin D status with reduced muscle strength and increased fall risk in older adults, and supplementation in deficient older people appears to reduce falls. This is why some falls-prevention programmes in the UK now include vitamin D supplementation as part of their advice.

    Mood and depression (mixed evidence)

    There’s a consistent observational association between low vitamin D status and depression, but randomised trials of vitamin D supplementation as a treatment for depression have produced mixed results. The current consensus is that correcting a deficiency may help mood in people who were deficient, but vitamin D is not a substitute for evidence-based treatments for clinical depression.

    Cardiovascular health (mixed evidence)

    Observational studies link low vitamin D to higher cardiovascular risk, but large trials of supplementation (such as VITAL in the US) have not consistently shown a reduction in heart attacks or strokes. The picture is unresolved.

    COVID-19 and other infections (uncertain)

    A large amount of pandemic-era research looked at vitamin D and COVID-19 outcomes. The honest summary: severe vitamin D deficiency appeared associated with worse outcomes, but supplementation results have been mixed, and the question of optimal dosing during acute illness remains unresolved.

    If you take only one thing from this section: vitamin D is genuinely important for bone health and immune function, and correcting a deficiency is worthwhile. But it’s not the cure-all that some wellness content makes it out to be.

    How much you need

    The recommendations vary between countries because experts disagree on what counts as “enough.” We list the UK NHS figures and the US figures, which are the two most commonly cited:

    Group NHS RNI (UK) US RDA
    Adults 19-64 10 µg (400 IU) 15 µg (600 IU)
    Adults 65+ 10 µg (400 IU) 20 µg (800 IU)
    Pregnant or breastfeeding 10 µg (400 IU) 15 µg (600 IU)
    Children 1-18 years 10 µg (400 IU) 15 µg (600 IU)
    Infants under 1 (formula-fed under 500ml/day) 8.5-10 µg 10 µg (400 IU)

    The Tolerable Upper Intake Level for adults is 100 micrograms (4,000 IU) per day from supplements, according to both UK Scientific Advisory Committee on Nutrition (SACN) and EFSA. Going above this for sustained periods without medical supervision can lead to vitamin D toxicity (hypercalcaemia).

    What blood levels mean

    If you’ve had a vitamin D blood test, the result is reported as 25-hydroxyvitamin D in nmol/L (UK) or ng/mL (US). The Department of Health uses these categories:

    • Below 25 nmol/L (10 ng/mL): deficient — supplementation generally recommended
    • 25-50 nmol/L (10-20 ng/mL): insufficient — supplementation generally recommended in winter
    • Above 50 nmol/L (20 ng/mL): adequate for most people

    Some clinicians and researchers prefer levels above 75 nmol/L (30 ng/mL), but this is debated. The threshold for “optimal” depends on which outcome you’re optimising for (bone, immune, all-cause mortality), and the evidence isn’t settled.

    Where to get it

    From sunlight (when latitude and lifestyle permit)

    In the summer in the UK, 10-15 minutes of midday sun on bare forearms a few times a week is generally enough for most people to make adequate vitamin D. Several caveats:

    • The further north you are, the harder this is — in Scotland, sun-derived vitamin D production essentially stops from October to April
    • People with darker skin need significantly more sun exposure to produce the same amount of vitamin D
    • Sunscreen, clothing coverage, glass windows, and air pollution all reduce production
    • Older adults’ skin makes vitamin D less efficiently
    • People who work indoors, cover up for cultural or religious reasons, or who are housebound get little to none

    From food

    Vitamin D is naturally present in a relatively small number of foods. Approximate amounts per typical serving:

    Food Vitamin D (µg per serving)
    Cooked oily fish (salmon, sardines, mackerel, herring) — 100g 10-25 µg
    Cod liver oil — 1 tsp (5ml) 11-12 µg
    Egg yolk — 1 large 1-2 µg
    Fortified breakfast cereal (UK varies) — 30g 1-2 µg
    Fortified plant milk — 250ml 1.5-2 µg
    UV-exposed mushrooms — 100g 5-10 µg (variable)
    Beef liver — 100g 1-2 µg

    A reality check: hitting the 10 µg NHS recommendation from food alone is genuinely difficult unless you’re eating oily fish three or four times a week. Most UK adults eat oily fish less than once a week.

    From supplementation

    For most UK adults, supplementation is the easiest reliable source of vitamin D, especially from October to March. The NHS specifically advises that:

    • Everyone in the UK should consider a 10 µg (400 IU) supplement during autumn and winter
    • People at higher risk of deficiency should consider taking it year-round
    • People with very limited sun exposure (housebound, cover up for cultural reasons, dark skin) should take it year-round

    Who’s at higher risk of deficiency

    Some groups are more likely to be deficient and should pay particular attention:

    • People with darker skin living in the UK — melanin reduces vitamin D production from sunlight
    • People who cover most of their skin for cultural or religious reasons
    • Housebound or institutionalised people with limited outdoor time
    • People aged 65+ — skin produces less efficiently
    • Pregnant and breastfeeding women — needs are higher
    • People with malabsorption conditions (Crohn’s, coeliac, gastric bypass) — absorb less of what they take in
    • People taking certain medications (some anticonvulsants, glucocorticoids) — increased breakdown
    • People with very low body weight or very high body weight — different mechanisms in each case

    If you’re in any of these groups, it’s worth asking your GP for a vitamin D blood test, which is available on the NHS.

    How to choose a supplement

    If you’ve decided to supplement, the choices come down to:

    Form

    D3 over D2 for most people. D3 is more effective at raising and maintaining blood vitamin D levels. Vegan D3 made from lichen is widely available and works the same as animal-derived D3.

    Dose

    For general winter maintenance in a UK adult without known deficiency: 10-25 µg (400-1,000 IU) per day is sensible. The NHS minimum is 10 µg, but many experts consider 20-25 µg more reflective of current evidence for optimal status.

    If you have a known deficiency, your GP may recommend higher doses (often 25-75 µg / 1,000-3,000 IU daily, sometimes higher loading doses short-term). Don’t self-prescribe high doses without guidance — vitamin D is fat-soluble and accumulates in the body, so toxicity is possible at sustained high doses.

    Avoid the very-high-dose products (10,000+ IU) marketed online unless prescribed.

    Quality markers

    • Third-party tested. Look for brands that publish independent lab testing or hold Informed Sport / NSF certification.
    • Pure form with sensible carrier. Vitamin D is fat-soluble, so capsules with an oil base (olive oil, MCT oil, coconut oil) absorb well. Tablet forms work too but should be taken with a fat-containing meal.
    • No proprietary blends. The label should state exactly how much vitamin D is in each capsule/drop.
    • Reasonable price. Vitamin D is one of the cheapest supplements to produce. Anything significantly more than £0.05-£0.10 per 1,000 IU daily dose is likely overpriced for what it is.
    • D3 + K2 combinations are popular and have a plausible rationale (K2 helps direct calcium to bones rather than soft tissues), but evidence for needing the combination in most people is weaker than the marketing suggests. A plain D3 product from a reputable brand is fine for most.

    Avoid

    • “Liposomal vitamin D” at premium prices — the absorption advantage is poorly evidenced for fat-soluble vitamins, which are already well-absorbed when taken with a meal
    • Combination products that hide vitamin D inside a 15-ingredient “immune booster” with vague proprietary amounts
    • Mega-dose loading regimens (300,000+ IU monthly) unless prescribed for a specific reason
    • Products without batch numbers and expiry dates clearly printed

    When to take it

    • With a meal containing fat — improves absorption
    • Time of day doesn’t matter much. Some people report it affects sleep if taken late, but the evidence is anecdotal
    • Daily is more consistent than weekly or monthly mega-doses for keeping levels steady, though both work

    Signs and symptoms of deficiency

    Vitamin D deficiency is often called “silent” because symptoms develop slowly. Possible signs include:

    • Bone or muscle pain, particularly in the lower back, hips, or thighs
    • Muscle weakness, especially noticeable when climbing stairs or rising from a chair
    • Fatigue and low mood
    • More frequent illnesses or infections
    • Slow wound healing
    • Hair thinning (sometimes)
    • In children: developmental delays, dental issues, bowed legs in severe cases

    These symptoms are non-specific and could have many other causes. The only way to know for certain is a 25-hydroxyvitamin D blood test, which your GP can arrange.

    Interactions and cautions

    Vitamin D can interact with several conditions and medications:

    • Sarcoidosis, lymphoma, hyperparathyroidism, or kidney disease: vitamin D supplementation should only be done under medical supervision because of altered calcium handling
    • Thiazide diuretics: increased risk of high blood calcium
    • Digoxin: high vitamin D-induced calcium elevation can affect digoxin toxicity
    • Statins (atorvastatin): vitamin D can affect statin metabolism in some studies
    • Steroids (long-term): reduce vitamin D activation; people on long-term steroids may need higher intakes
    • Weight-loss medications (orlistat) and bile acid sequestrants: reduce fat-soluble vitamin absorption

    If you take any prescription medication or have a chronic condition, ask your GP or pharmacist before starting a high-dose vitamin D supplement.

    Frequently asked questions

    Should the whole family take vitamin D in winter?
    NHS guidance is that everyone in the UK aged 1 and over should consider a 10 µg supplement during autumn and winter. Breastfed babies should be given vitamin D drops from birth (8.5-10 µg) unless they’re getting formula with sufficient added vitamin D.

    Can I just spend more time in the sun?
    In summer, yes — modest midday sun exposure on bare forearms a few times a week is generally enough for most people. In winter at UK latitudes, no — the UVB intensity from October to April is too weak to make significant amounts of vitamin D, even on a bright cloudless day.

    Does sunbed exposure help?
    Sunbeds do produce UVB and so will increase vitamin D, but the skin cancer risk from sunbed use is well-established and outweighs the benefit when supplements are a cheap and safe alternative.

    Is too much vitamin D dangerous?
    Yes, though deliberately overdosing is hard. Sustained intakes above 100 µg (4,000 IU) per day from supplements without monitoring can cause hypercalcaemia (high blood calcium), with symptoms including nausea, vomiting, weakness, frequent urination, and in severe cases kidney damage. Stick to the recommended range unless you’re being monitored.

    Vitamin D3 vs D2 — does the source matter?
    D3 (cholecalciferol) is generally more effective at raising blood levels and maintaining them. D2 (ergocalciferol) works but appears to be roughly 2-3 times less effective per unit. Vegan D3 from lichen is now widely available, so vegans don’t need to choose D2 by default.

    Do I need vitamin K2 with my D3?
    The theoretical rationale (K2 directs calcium to bones rather than arteries) is plausible, but the human evidence for needing K2 alongside D3 supplementation is weaker than supplement marketing suggests. A varied diet with green vegetables and fermented foods usually provides adequate K2. The combination products are fine to take but not clearly necessary for most people.

    Does vitamin D help with hair loss?
    There’s a consistent association between low vitamin D status and several hair loss conditions, including alopecia areata. Whether supplementation reverses hair loss in people who aren’t deficient is much less clear. If your hair is thinning, getting your vitamin D tested is reasonable; expecting D supplementation alone to regrow lost hair generally isn’t.

    Can I take vitamin D with my other supplements?
    Generally yes, especially with calcium, magnesium, and vitamin K. Take with a meal containing fat for best absorption.

    Where to go from here

    • If you suspect deficiency: ask your GP for a 25-hydroxyvitamin D blood test
    • For winter maintenance: consider a 10-25 µg D3 supplement from October to March
    • For year-round maintenance if you’re in a higher-risk group: same dose, year-round
    • For diagnosed deficiency: follow your GP’s recommended dose

    Related reading on Nutrition Encyclopedia

    Primary sources

    • NHS — Vitamin D guidance
    • Scientific Advisory Committee on Nutrition (SACN) — Vitamin D and Health report
    • NIH Office of Dietary Supplements — Vitamin D fact sheet for health professionals
    • European Food Safety Authority — authorised health claims register
    • Cochrane reviews on vitamin D supplementation
    • USDA FoodData Central — for food vitamin D content

    Information on this page is for general guidance and is not a substitute for medical advice. Speak to your GP if you suspect a vitamin D deficiency or before starting supplementation above 10 µg (400 IU) per day, especially if you take medication or have a health condition.

    Last updated: May 2026

  • Magnesium — The Complete Guide

    Magnesium — The Complete Guide

    Magnesium is involved in more than 300 enzymatic reactions in the human body, including processes that affect muscle function, nerve signalling, blood sugar regulation, blood pressure, and the production of energy and protein. Despite being one of the most abundant minerals on earth, a substantial portion of UK and US adults consistently fall short of the recommended daily intake — partly because modern wheat-based diets contain less magnesium than they used to, partly because magnesium is one of the first things lost in food processing.

    This guide covers what magnesium does, how much you need, the best food sources, and — for those who don’t get enough from diet — how to choose a supplement that actually works rather than one that wastes your money on a poorly absorbed form.

    Quick disclaimer: Information here is for general guidance and is not medical advice. Magnesium supplementation interacts with several medications and conditions. If you have kidney disease, heart conditions, or take prescription medication, speak to your GP or pharmacist before starting a magnesium supplement above the dietary level.

    What magnesium does in the body

    The European Food Safety Authority has authorised the following health claims for magnesium:

    • Magnesium contributes to a reduction of tiredness and fatigue
    • Magnesium contributes to electrolyte balance
    • Magnesium contributes to normal energy-yielding metabolism
    • Magnesium contributes to normal functioning of the nervous system
    • Magnesium contributes to normal muscle function
    • Magnesium contributes to normal protein synthesis
    • Magnesium contributes to normal psychological function
    • Magnesium contributes to the maintenance of normal bones and teeth
    • Magnesium has a role in the process of cell division

    That’s an unusually broad list — magnesium genuinely is involved in a lot of basic biological machinery. Beyond the EFSA list, several other potential roles are being actively researched and we summarise the current evidence below.

    Sleep quality (modest evidence, mostly in older adults)

    Magnesium supplementation in older adults with sleep difficulties has shown modest improvements in sleep quality in several small randomised trials. The mechanism is plausible — magnesium activates the parasympathetic nervous system and regulates GABA receptors, the same neurotransmitter system that prescription sleep medications target. Whether magnesium helps sleep in younger adults without deficiency is less clear, but it’s a reasonable thing to try if you have sub-optimal sleep and your magnesium intake is on the low side.

    Anxiety (limited but suggestive evidence)

    Several reviews have found a modest association between low magnesium status and anxiety, and limited trial evidence suggests supplementation may help in some people. The effect is not large or consistent enough to recommend magnesium as a treatment for anxiety, but it’s worth getting your intake up to recommended levels if you have anxiety symptoms.

    Migraine prevention (reasonable evidence)

    Magnesium is one of the few nutrients with reasonable evidence for migraine prevention, and the American Academy of Neurology lists it among possible preventive treatments. Typical doses studied for migraine are 400-600 mg per day of supplementary magnesium — significantly higher than the dietary RDA — and should only be undertaken with medical advice because of side effects at these doses.

    Blood pressure (modest evidence)

    A meta-analysis of randomised trials found that magnesium supplementation produces small reductions in both systolic and diastolic blood pressure, particularly in people with hypertension or insulin resistance. The effect is modest (a few mmHg) and shouldn’t replace prescribed antihypertensive medication, but as part of overall lifestyle measures it has some support.

    Type 2 diabetes risk (reasonable observational evidence)

    Higher dietary magnesium intake is associated with lower risk of developing type 2 diabetes in several large cohort studies. Whether supplementation reduces risk in people already at high risk is less clear, but ensuring adequate intake is sensible.

    Muscle cramps (mixed evidence, except in pregnancy)

    The popular use of magnesium for muscle cramps is supported in pregnant women (some evidence of benefit) but not consistently in the general population. The Cochrane review found magnesium unlikely to help leg cramps in non-pregnant older adults. If you get severe cramps with exercise, hydration and overall electrolyte balance is usually more important than magnesium alone.

    Constipation (well-established, depending on form)

    Magnesium oxide and magnesium citrate at higher doses (hundreds of milligrams) reliably loosen stools — they’re commonly used as over-the-counter laxatives. This is a known property to be aware of when choosing a supplement: oxide is poorly absorbed and most of the dose ends up doing this. Glycinate, malate, and threonate are far gentler.

    How much you need

    The UK NHS Reference Nutrient Intake (RNI) for adults:

    Group NHS RNI (UK) US RDA
    Men 19+ 300 mg 400-420 mg
    Women 19+ 270 mg 310-320 mg
    Pregnancy 270 mg 350-360 mg
    Breastfeeding 320 mg 310-320 mg
    Children 1-3 85 mg 80 mg
    Children 4-6 120 mg 130 mg
    Children 7-10 200 mg 240 mg
    Children 11-14 (boys/girls) 280/280 mg 410/360 mg

    Notice the US figures are notably higher than the UK ones — this is one of the larger international discrepancies in nutrient recommendations. The honest answer is that the “right” amount is debated, but if your diet is providing well below the UK RNI on most days, supplementing the difference is reasonable.

    Tolerable Upper Intake Level (UL) for supplementary magnesium: 250 mg per day according to UK SACN, 350 mg per day according to US authorities. Above this, the main risk is digestive disturbance (diarrhoea), but very high doses can cause more serious effects. Magnesium from food doesn’t have an upper limit because food forms are absorbed differently from supplemental forms.

    What blood tests can and can’t tell you

    A standard serum magnesium test is widely available but only catches severe deficiency, because the body tightly regulates blood levels by pulling magnesium from bones if intake is low. A red blood cell magnesium test or an erythrocyte magnesium test gives a better picture of overall status but is not routinely available on the NHS. In practice, dietary intake is usually a more useful indicator than a blood test for mild-to-moderate insufficiency.

    Where to get it from food

    Magnesium is widely distributed across plant foods, particularly leafy greens, nuts, seeds, whole grains, and legumes. Approximate amounts per typical serving:

    Food Magnesium per serving
    Pumpkin seeds — 30g (small handful) 165 mg
    Almonds — 30g (small handful) 80 mg
    Cashews — 30g 75 mg
    Spinach (cooked) — 100g 80 mg
    Black beans (cooked) — 100g 70 mg
    Edamame (cooked) — 100g 60 mg
    Dark chocolate (70%+) — 30g 65 mg
    Brown rice (cooked) — 100g 40 mg
    Wholemeal bread — 2 slices 45 mg
    Avocado — 1 medium 60 mg
    Banana — 1 medium 30 mg
    Salmon (cooked) — 100g 30 mg
    Yoghurt (plain) — 200g 40 mg
    Tofu (firm) — 100g 35 mg

    Hitting the UK RNI (270-300 mg) from food is achievable with a varied diet — for example, two slices of wholemeal toast + a banana for breakfast (75 mg), a handful of almonds as a snack (80 mg), spinach with dinner (80 mg), and a small piece of dark chocolate (60 mg) gets you to roughly 295 mg without supplementation.

    Why intake has dropped

    Several factors contribute to lower magnesium intake than in previous generations:

    • Whole-grain bread and brown rice have largely been replaced by refined white versions in many diets — refining removes most of the magnesium
    • Modern wheat varieties contain less magnesium than older varieties grown in less-depleted soils
    • Processed foods are typically low in magnesium
    • Soft water has less magnesium than hard water (a small but cumulative source of dietary magnesium in some regions)
    • High-stress lifestyles can increase urinary magnesium loss

    Who’s at higher risk of insufficiency

    Some groups are more likely to fall short:

    • People with type 2 diabetes — both because of higher urinary losses and because metformin can reduce absorption
    • People with gastrointestinal conditions (Crohn’s, coeliac, after gastric bypass)
    • People taking proton pump inhibitors (long-term PPI use is associated with low magnesium)
    • People taking certain diuretics (especially loop and thiazide diuretics)
    • Heavy alcohol users
    • Older adults (lower intake + reduced absorption)
    • People who restrict whole grains, nuts, or leafy greens for any reason
    • Athletes with high sweat losses

    How to choose a supplement

    The single biggest decision in magnesium supplementation is choosing the form. This matters more than brand, dose, or price — get the form wrong and most of what you take won’t actually be absorbed.

    The forms, ranked roughly by bioavailability and tolerability

    Magnesium glycinate (also called bisglycinate) — magnesium bonded to two molecules of the amino acid glycine. Generally the best default form: well absorbed, very gentle on the digestive system, doesn’t cause diarrhoea at normal doses, and the glycine itself has a mild calming effect that some people notice. Good for evening use if you’re hoping for any sleep benefit. The main drawback is it’s more expensive per milligram of elemental magnesium than oxide.

    Magnesium citrate — magnesium bonded to citric acid. Well absorbed, but at higher doses (above ~300 mg elemental) it has a laxative effect that’s useful if you want it, unpleasant if you don’t. A reasonable budget-friendly option at moderate doses.

    Magnesium malate — bonded to malic acid. Well absorbed, generally well tolerated. Sometimes recommended for daytime use (malic acid is involved in energy metabolism), and some people with fibromyalgia find it helpful, though evidence for the specific fibromyalgia claim is limited.

    Magnesium L-threonate — a newer form bonded to threonic acid, marketed as crossing the blood-brain barrier better than other forms and supporting cognitive function. The lab evidence is interesting but human trial evidence is limited and the form is significantly more expensive. Possibly worth trying if cognitive support is your specific goal; not necessary for general supplementation.

    Magnesium taurate — bonded to taurine. Some evidence for cardiovascular benefits given taurine’s separate effects. Niche but reasonable.

    Magnesium oxide — widely sold because it’s cheap and contains a high percentage of elemental magnesium by weight. Poorly absorbed (around 4% bioavailability in some studies), so most of the dose passes through and acts as a laxative. Useful if you want a laxative, not useful as a supplement.

    Magnesium sulphate (Epsom salts) — generally used in baths rather than orally. Trans-dermal absorption of magnesium from Epsom salt baths is debated and probably minimal, but the warm water itself helps muscle relaxation.

    Avoid: “Magnesium chelate” without specifying which chelate (usually a marketing term — could be anything), proprietary blends with multiple magnesium forms in undisclosed amounts, and aspartate (some safety concerns about excitotoxicity in high doses, though probably minor in practice).

    Dosage

    For general intake-topping: 100-200 mg of elemental magnesium per day from supplements is a sensible range for most adults. This brings most people up to or comfortably past the RNI without approaching the upper limit.

    For specific therapeutic uses (migraine prevention, evening sleep support, etc.), higher doses are sometimes used but should be approached with medical advice.

    Pay attention to “elemental magnesium” vs “total compound” on labels. A capsule containing 1,000 mg of magnesium glycinate provides only about 140 mg of elemental magnesium (the rest is glycine). The label should make this clear; if it doesn’t, calculate it or pick a different brand.

    Quality markers

    • Third-party tested (USP Verified, NSF Certified, or independent lab results published)
    • Clear listing of elemental magnesium per serving
    • Single form per product (not a “magnesium blend”)
    • No proprietary blends
    • Reasonable price — glycinate from a reputable brand costs around £0.10-£0.20 per 100 mg elemental dose

    When and how to take it

    • With food — improves tolerance, especially for forms that can cause digestive symptoms
    • Time of day: glycinate in the evening if hoping for sleep effects; citrate in the morning if you want the mild laxative effect; otherwise whenever you’ll remember to take it consistently
    • Split doses if taking more than 200 mg elemental — improves absorption and reduces digestive effects
    • Daily, not all-at-once — magnesium doesn’t have a meaningful loading effect; consistent daily intake matters

    Signs of insufficiency

    Mild magnesium insufficiency often produces no obvious symptoms. More noticeable signs of low intake can include:

    • Muscle twitches, cramps, or tics
    • Fatigue and low energy
    • Poor sleep quality
    • Headaches
    • Sensitivity to noise
    • Low mood or anxiety
    • Constipation (paradoxically — magnesium is needed for healthy bowel function even though too much causes the opposite)
    • Numbness or tingling (severe deficiency)
    • Abnormal heart rhythms (severe deficiency — get medical advice)

    Note these are non-specific. If symptoms are significant or persistent, see your GP rather than self-diagnosing a magnesium deficiency.

    Interactions and cautions

    Magnesium supplementation can interact with several conditions and medications:

    • Kidney disease: people with reduced kidney function should not supplement magnesium without medical advice — risk of accumulation and toxicity
    • Antibiotics: magnesium can reduce absorption of tetracycline and quinolone antibiotics. Take at least 2 hours apart.
    • Bisphosphonates (osteoporosis medication): same — separate doses by 2+ hours
    • Diuretics: some diuretics (loop, thiazide) increase magnesium loss; potassium-sparing diuretics can increase magnesium retention
    • Proton pump inhibitors (omeprazole etc.): long-term use associated with low magnesium
    • Diabetes medication: magnesium can affect blood sugar; monitor if you have diabetes
    • Blood pressure medication: magnesium may have additive effects

    If you take any prescription medication or have a chronic condition, ask your GP or pharmacist before starting a magnesium supplement above the dietary level.

    Frequently asked questions

    What’s the difference between magnesium glycinate and bisglycinate?
    None — they’re the same thing. “Bisglycinate” specifies that two glycine molecules are bonded to one magnesium ion, which is the standard form. Brands use the names interchangeably.

    Will magnesium really help me sleep?
    Possibly, if your intake is on the low side. The evidence is strongest in older adults with sleep difficulties. In younger adults with adequate intake, the effect is more modest and may be largely a placebo or relaxation response. Magnesium glycinate taken about an hour before bed is the form most often used for this purpose. It’s worth trying for a few weeks; don’t expect a prescription-sleep-medication-strength effect.

    Can I get enough magnesium from food alone?
    For most people, yes, with a varied diet that includes leafy greens, nuts/seeds, whole grains, and legumes. If your diet is heavy in processed foods and refined grains, hitting the RNI from food alone is harder.

    Is magnesium safe to take long-term?
    For most healthy adults, supplementing within the recommended ranges (under the 250-350 mg upper limit) appears safe long-term. People with kidney disease or on certain medications should not supplement without medical advice.

    Will taking magnesium give me diarrhoea?
    Depends on the form and dose. Magnesium oxide and citrate at higher doses commonly do. Magnesium glycinate, malate, and threonate are far gentler. If you experience loose stools, switch form or reduce dose.

    Can I take magnesium with calcium?
    Yes — they’re sometimes paired in supplements. Some people prefer to take calcium and magnesium at different times of day because they compete for absorption at very high doses, but this matters less at typical supplement doses.

    Does magnesium spray or oil work?
    Trans-dermal magnesium products are popular but the evidence for meaningful absorption through skin is weak. The relaxation effect people report from Epsom salt baths is probably mostly from the warm water. If you want measurable magnesium intake, oral supplements are more reliable.

    Should athletes take magnesium?
    Athletes lose more magnesium in sweat and often benefit from being at the higher end of the intake range. Whether supplementation improves performance specifically is less clear unless the athlete is deficient.

    Where to go from here

    • For dietary improvement: aim to add a daily serving of pumpkin seeds, almonds, or leafy greens — small habit, meaningful magnesium boost
    • For supplementation: start with 100-200 mg elemental magnesium glycinate per day, with food
    • For sleep: try glycinate in the evening for 2-4 weeks
    • For migraine prevention: discuss with your GP — therapeutic doses (400+ mg) need supervision

    Related reading on Nutrition Encyclopedia

    Primary sources

    • NHS — Magnesium guidance
    • Scientific Advisory Committee on Nutrition (UK)
    • NIH Office of Dietary Supplements — Magnesium fact sheet for health professionals
    • European Food Safety Authority — authorised health claims register
    • Cochrane reviews on magnesium supplementation for various indications
    • USDA FoodData Central — for food magnesium content

    Information on this page is for general guidance and is not a substitute for medical advice. Please speak to your GP or pharmacist before starting magnesium supplementation if you have kidney disease, heart conditions, or take prescription medication.

    Last updated: May 2026