NOW Foods Cal-Mag Caps

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.

Calcium· evidence: Moderate

Calcium is the main mineral in bones and teeth and is also needed for muscles, nerves and blood clotting. Adults need about 700 mg a day in the UK, which most people get from dairy, fortified plant milks, tofu, bread made with fortified flour and green vegetables.

Calcium supplements help people whose diets are genuinely low, for example some vegans or people who avoid dairy, and are sometimes prescribed with vitamin D for people with osteoporosis. For well-fed adults, reviews have found that extra calcium makes little difference to fracture risk.

Food is the preferred source. Different forms (carbonate, citrate) give different amounts of elemental calcium; citrate is easier to absorb without food.

Typical dose: Adults need 700 mg a day from all sources (NRV on labels: 800 mg). Supplements usually give 200 to 1,000 mg.

Safety: The FSA advises that 1,500 mg a day or less from supplements is unlikely to cause harm. High doses can cause constipation and wind. Calcium reduces absorption of some medicines (such as thyroxine, some antibiotics and bisphosphonates) and iron, so take them at different times and check with a pharmacist. People with a history of kidney stones or high blood calcium should speak to their GP.

Research we looked at:
NHS. Calcium. nhs.uk/conditions/vitamins-and-minerals/calcium
Bolland MJ, Leung W, Tai V, et al. Calcium intake and risk of fracture: systematic review. BMJ 2015;351:h4580.
EFSA NDA Panel. Scientific opinion on the tolerable upper intake level of calcium. EFSA Journal 2012;10(7):2814.

Vitamin D3· evidence: Strong

Vitamin D3 (cholecalciferol) is the form the skin makes from sunlight. In the UK there is not enough strong sunlight from about October to March, so many people have low levels over winter. Good-quality trials show supplements reliably raise blood levels and correct deficiency, and that matters for bone health in people who are low.

The NHS advises everyone to consider 10 µg (400 IU) a day in autumn and winter, and all year round for people who get little sun, cover their skin, have darker skin or live in care homes. For people who already have adequate levels, large trials have not shown that extra vitamin D prevents falls, fractures or other illness.

In short: a modest daily dose is sensible and cheap insurance for most UK adults in winter. Very high doses are not better and should only be taken on medical advice.

Typical dose: 10 µg (400 IU) a day is the NHS advice for adults and children over 1. Doses of 25 µg (1,000 IU) to 50 µg (2,000 IU) are common and safe for adults. Babies under 1 need 8.5 to 10 µg a day unless they have more than 500 ml of formula.

Safety: Do not take more than 100 µg (4,000 IU) a day without medical advice (FSA/NHS); children aged 1 to 10 should not have more than 50 µg, and babies under 1 no more than 25 µg. Long-term very high intake can raise blood calcium, which can damage the kidneys and heart. People with kidney disease, sarcoidosis or high calcium levels should speak to their GP first.

Research we looked at:
NHS. Vitamin D. nhs.uk/conditions/vitamins-and-minerals/vitamin-d
Scientific Advisory Committee on Nutrition (SACN). Vitamin D and Health. 2016.
EFSA NDA Panel. Scientific opinion on the tolerable upper intake level for vitamin D. EFSA Journal 2023;21(8):8145.
Bolland MJ, Grey A, Avenell A. Effects of vitamin D supplementation on musculoskeletal health: a systematic review, meta-analysis, and trial sequential analysis. Lancet Diabetes Endocrinol 2018;6(11):847-858.

Zinc· evidence: Moderate

Zinc is a trace mineral needed for the immune system, skin, wound healing and many enzymes. Men need about 9.5 mg a day and women 7 mg in the UK, mostly from meat, shellfish, dairy, bread and cereals. Vegans and vegetarians can fall short because plant foods contain phytates that reduce absorption.

Supplements help people whose intake is low. Zinc lozenges taken at the very start of a cold have been studied with mixed results; tablets swallowed every day by well-fed people are not shown to add much.

Long-term high doses cause problems, mainly by blocking copper absorption, so more is not better.

Typical dose: Adults need about 7 mg (women) to 9.5 mg (men) a day from all sources (NRV on labels: 10 mg). Supplements usually give 5 to 25 mg.

Safety: The NHS advises not taking more than 25 mg of zinc a day from supplements unless a doctor advises it. Long-term high doses can cause copper deficiency, anaemia and weakened immunity. Zinc can upset the stomach if taken without food, and it reduces absorption of some antibiotics.

Research we looked at:
NHS. Others: vitamins and minerals (zinc). nhs.uk/conditions/vitamins-and-minerals/others
EFSA NDA Panel. Scientific opinion on dietary reference values for zinc. EFSA Journal 2014;12(10):3844.
Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open 2017;8(5):2054270417694291.

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