Last updated: October 2026
Yes, you can take magnesium and calcium together, and many bone supplements combine them. Large doses taken at the same moment may compete for absorption, so some people split them across the day. Most adults can get the 700mg of calcium they need from food, so don’t add a calcium supplement without good reason or advice.
Below: absorption, the popular 2:1 ratio, how much you need, food sources, timing and calcium supplement safety.
Can you take magnesium and calcium together?
Yes. There’s no known harmful interaction between the two at normal doses, and “calcium, magnesium and zinc” tablets are widely sold in the UK. If you take a combined product at the dose on the label, there’s no need to separate them. Weighing up zinc too? See magnesium vs zinc.
Do magnesium and calcium compete for absorption?
Less than the internet suggests. A 1991 review of magnesium absorption found that calcium and magnesium do interact in the gut, but said the nature of the interaction couldn’t be explained by the data available.
Studies that measured it directly are small but reassuring:
- In 26 girls given either a placebo or an extra 1,000mg of calcium a day for two weeks, magnesium absorption was much the same (50% on placebo, 55% with the extra calcium).
- In a stable isotope study, raising calcium from 800mg to 1,800mg a day didn’t significantly change how magnesium was absorbed or used.
- In the other direction, giving adult men around 800mg of magnesium a day didn’t change how much calcium they absorbed.
The more practical limit is calcium itself: it’s absorbed best in smaller amounts, and a clinical review advises no more than 500mg of elemental calcium at a time. That’s the main reason to split a large calcium dose, rather than any battle with magnesium.
Is there an ideal calcium to magnesium ratio?
You’ll often see “2:1 calcium to magnesium” quoted as the perfect ratio. It comes mainly from a 2016 review, which suggested an intake ratio of around 2 to 1 may be optimal, and that ratios below 1.7 or above 2.8 could be unhelpful. Those figures come largely from population studies, and the authors called for more research.
In practice, UK guidance doesn’t set a ratio. The NHS amounts work out at roughly 2.3 to 1 for men (700mg calcium, 300mg magnesium) and 2.6 to 1 for women (700mg and 270mg), so simply meeting both from a varied diet lands you near the popular figure anyway. Counting milligrams to hit an exact ratio isn’t necessary. Our magnesium and bone health guide takes the same view.
How much magnesium and calcium do you need?
| Calcium | Magnesium | |
|---|---|---|
| Adults need (NHS) | 700mg a day | 300mg a day (men), 270mg a day (women) |
| From supplements | 1,500mg or less a day is unlikely to cause harm | 400mg or less a day is unlikely to cause harm |
| Too much can cause | Stomach pain and diarrhoea (over 1,500mg a day) | Diarrhoea (over 400mg for a short time) |
The NHS says you should be able to get all the calcium you need from your daily diet. If you’re at risk of osteoporosis or on an osteoporosis medicine, your doctor may suggest around 1,000mg a day. Add up every product you take, including multivitamins. See types of magnesium and signs of magnesium deficiency.
Foods rich in calcium and magnesium
Dairy is rich in calcium but fairly low in magnesium, while nuts and seeds are the reverse, so a mix of both covers you well. Figures are approximate, from USDA food data scaled to typical UK portions.
| Food and portion | Calcium | Magnesium |
|---|---|---|
| Calcium-set tofu, 100g | about 680mg | 58mg |
| Milk, 200ml glass | 240mg | 22mg |
| Sardines with bones, half a tin (60g) | 229mg | 23mg |
| Plain yoghurt, 150g pot | 182mg | 18mg |
| Kale, boiled, 100g | 150mg | 25mg |
| Spinach, boiled, 90g | 122mg (poorly absorbed) | 78mg |
| Chia seeds, 1 tablespoon (15g) | 95mg | 50mg |
| Almonds, 30g handful | 80mg | 84mg |
| Broccoli, boiled, 85g | 34mg | 18mg |
| Pumpkin seeds, 30g | 16mg | 165mg |
Calcium-fortified plant drinks typically provide 120mg to 190mg per 100ml, but check the label, as many organic versions aren’t fortified. Spinach, beans, nuts and seeds contain oxalates or phytates, which reduce how much of their calcium you absorb. For a longer list, see foods high in magnesium.
Magnesium and calcium for bones
Both minerals have authorised health claims for bones. Calcium is needed for the maintenance of normal bones. Magnesium contributes to the maintenance of normal bones. Vitamin D, which helps your body absorb calcium, completes the trio. See magnesium and vitamin D.
For preventing osteoporosis, the NHS focuses on regular weight-bearing and resistance exercise, a balanced diet with enough calcium, 10 micrograms of vitamin D a day (it suggests considering a supplement, especially in autumn and winter), not smoking and drinking less. Supplements aren’t a treatment for osteoporosis, and the evidence for calcium tablets alone is weaker than many people assume: a 2017 expert consensus concluded that calcium alone for fracture reduction isn’t supported, while calcium with vitamin D gives a modest reduction. Read more in vitamin D in winter.
Magnesium and calcium for cramps and sleep
Calcium contributes to normal muscle function, and so does magnesium. That’s why the pair often appear in products aimed at cramps. The research is underwhelming, though: a 2020 Cochrane review found magnesium unlikely to give meaningful protection from cramps in older adults. Our guide to magnesium for cramps covers what else to try.
There’s no good trial evidence that taking calcium and magnesium together improves sleep. Magnesium on its own has some early research, covered in magnesium for sleep.
Best time to take magnesium and calcium
- Combined tablet at label dose: take it whenever you’ll remember, usually with a meal.
- Separate supplements: a simple split is calcium with breakfast or lunch and magnesium in the evening.
- Calcium carbonate is best taken with food. Calcium citrate can be taken with or without food.
- Over 500mg of calcium a day from supplements: split it into two doses.
Many people find glycinate gentler on the stomach than oxide or citrate. See the best time to take magnesium, magnesium glycinate, magnesium citrate and magnesium oxide.
Our Magnesium Glycinate Sleep Complex is an evening drink giving 148mg of magnesium per serving from bisglycinate and citrate, with glycine, L-theanine and botanicals. It contains no calcium, so it sits easily alongside a calcium-rich diet or a separate calcium supplement your GP has advised. Magnesium contributes to the maintenance of normal bones and to normal muscle function.
Calcium supplement safety and medicines
Calcium tablets carry a few trade-offs worth knowing.
- Kidney stones. In a large US trial, 36,282 postmenopausal women took 1,000mg of calcium plus 400 IU of vitamin D or a placebo for seven years. The supplement group had a 17% higher risk of kidney stones. If you’ve had stones or have kidney disease, ask your GP first.
- Stomach side effects. Digestive complaints are a recognised side effect. One review of the trials found hospital admissions for gut problems roughly doubled in people taking calcium supplements.
- The heart debate. A 2010 meta-analysis linked calcium supplements taken without vitamin D to around a 30% higher relative risk of heart attack, and a 2019 umbrella review linked calcium plus vitamin D to a higher risk of stroke. A 2017 European consensus found the link not convincingly supported, and the Department of Health didn’t change its prescribing advice. It’s unsettled, which is another reason to favour food.
Medicines to space apart
- Levothyroxine for an underactive thyroid: the NHS lists calcium supplements and indigestion remedies among things that may not mix well with it. Ask your pharmacist how far apart to take them. See underactive thyroid symptoms.
- Ciprofloxacin: the NHS advises leaving 2 hours between calcium, zinc or iron supplements and your dose.
- Alendronic acid (a bisphosphonate for osteoporosis): take it on an empty stomach, 30 minutes before breakfast and any other medicines, and tell your doctor about supplements containing calcium, iron, magnesium or zinc.
Magnesium has its own list, covered in magnesium side effects. We don’t recommend our products during pregnancy or breastfeeding, and they’re for adults only.
FAQs
Can you take magnesium and calcium together?
Yes. There’s no known harmful interaction at normal doses, and many supplements combine them. If you take large separate doses, you can split them across the day.
What is the best ratio of calcium to magnesium?
A ratio of about 2 to 1 is often quoted, but the evidence is limited. Meeting the NHS amounts of 700mg calcium and 270mg to 300mg magnesium puts you close to it anyway.
Does calcium stop magnesium being absorbed?
Not much at normal intakes. Small controlled studies found extra calcium didn’t significantly change magnesium absorption, and extra magnesium didn’t change calcium absorption.
Should I take magnesium and calcium in the morning or at night?
Either works. A simple routine is calcium with breakfast or lunch and magnesium in the evening. Keep each calcium dose to 500mg or less.
Do I need a calcium supplement?
Most adults don’t. The NHS says you should be able to get the 700mg you need from your diet. Your GP may advise a supplement if you’re at risk of osteoporosis or eat little dairy or fortified food.
Can I take magnesium, calcium and zinc together?
Yes, combined tablets are common. Stick to the label dose and keep zinc supplements to 25mg a day or less, as the NHS advises.
Sources
- NHS. Vitamins and minerals: calcium.
- NHS. Vitamins and minerals: others (magnesium and zinc).
- NHS. Preventing osteoporosis.
- NHS. Levothyroxine; Ciprofloxacin with other medicines and supplements; Alendronic acid with other medicines and supplements.
- British Dietetic Association. Calcium: food fact sheet.
- Royal Osteoporosis Society. Calcium.
- Rosanoff A, Dai Q, Shapses SA (2016). Essential nutrient interactions: does low or suboptimal magnesium status interact with vitamin D and/or calcium status? Advances in Nutrition.
- Hardwick LL et al (1991). Magnesium absorption: mechanisms and the influence of vitamin D, calcium and phosphate. Journal of Nutrition.
- Andon MB et al (1996). Magnesium balance in adolescent females consuming a low- or high-calcium diet. American Journal of Clinical Nutrition.
- Sojka J et al (1997). Magnesium kinetics in adolescent girls determined using stable isotopes: effects of high and low calcium intake. American Journal of Physiology.
- Spencer H et al (1994). Effect of magnesium on the intestinal absorption of calcium in man. Journal of the American College of Nutrition.
- Straub DA (2007). Calcium supplementation in clinical practice: a review of forms, doses, and indications. Nutrition in Clinical Practice.
- Jackson RD et al (2006). Calcium plus vitamin D supplementation and the risk of fractures. New England Journal of Medicine.
- Bolland MJ et al (2010). Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ.
- Khan SU et al (2019). Effects of nutritional supplements and dietary interventions on cardiovascular outcomes: an umbrella review and evidence map. Annals of Internal Medicine.
- Reid IR, Bristow SM, Bolland MJ (2015). Calcium supplements: benefits and risks. Journal of Internal Medicine.
- Harvey NC et al (2017). The role of calcium supplementation in healthy musculoskeletal ageing. Osteoporosis International.
- Garrison SR et al (2020). Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews.
- US Department of Agriculture. FoodData Central (food values).
- Authorised health claims: Great Britain nutrition and health claims register.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex.
