Calcium Myths: Separating Facts from Fiction
Calcium is probably the best-known mineral of all, yet it attracts a surprising number of misunderstandings. Some people take high-dose supplements believing more is always better, while others avoid dairy for fear of kidney stones. Our editorial team looks at the most common calcium myths through the lens of current research and UK recommendations.
Why calcium matters for active people
Around 99 per cent of the body's calcium is stored in bones and teeth, where it provides structural strength. The remaining 1 per cent circulates in blood and tissues and is involved in muscle contraction, nerve signalling, blood clotting and hormone release. Blood calcium is tightly controlled, and if intake is low the body draws on the skeleton to keep it stable.
For people who train, calcium is relevant in two ways. First, peak bone mass is built during adolescence and early adulthood, and adequate calcium alongside weight-bearing exercise supports it. Second, athletes in low-energy states, such as endurance runners or those cutting weight, are at greater risk of stress fractures.
The UK reference nutrient intake for adults is 700 mg per day, a figure set by the Department of Health and still used in NHS guidance. Breastfeeding women have a higher requirement, and people with osteoporosis are often advised to aim for around 1,000 mg or more under medical guidance.
Sweat contains some calcium, and athletes who train for long periods in the heat may lose meaningful amounts. This is one reason why sports dietitians pay attention to intake in endurance athletes.
Myth 1: 'The more calcium, the stronger the bones'
Bones do not simply soak up whatever calcium they receive. Once needs are met, extra calcium has little additional effect on bone density. A large systematic review published in the BMJ (Tai et al., 2015) found that increasing calcium intake from food or supplements produced only small, non-progressive gains in bone mineral density of about 1 to 2 per cent.
A companion analysis (Bolland et al., 2015) found that dietary calcium intake was not associated with fracture risk, and that there was no strong evidence that supplements prevent fractures in the general population. The picture differs in frail, institutionalised older adults, where calcium combined with vitamin D has shown benefits in some trials.
Bone strength depends on many factors: mechanical loading, vitamin D status, protein intake, hormones such as oestrogen and testosterone, and overall energy availability. Calcium is necessary, but it is not sufficient on its own.
The practical message is to meet, rather than greatly exceed, your needs. For most healthy adults this is achievable from diet alone.
Myth 2: 'Calcium supplements are harmless'
For a long time, calcium tablets were considered completely benign. That view changed after a meta-analysis by Bolland and colleagues (2010) suggested that calcium supplements without vitamin D were associated with a modest increase in the risk of myocardial infarction. This finding is still debated, and other analyses have not confirmed it.
One proposed explanation is that a large single dose of supplemental calcium causes a temporary spike in blood calcium, which does not happen with food. In contrast, dietary calcium has not been linked to cardiovascular harm.
The Women's Health Initiative trial (Jackson et al., 2006) found that calcium with vitamin D slightly increased the risk of kidney stones. Constipation and bloating are also common, especially with calcium carbonate.
Supplements are still appropriate for many people, for example those with osteoporosis taking bone medicines, those who cannot meet needs through diet, or people with diagnosed deficiency. The key point is that they should be targeted rather than taken automatically.
Myth 3: 'Dairy causes kidney stones'
This myth has the relationship almost backwards. Most kidney stones are made of calcium oxalate, so it seems logical to cut calcium. However, a classic prospective study by Curhan and colleagues (1993) found that men with higher dietary calcium intake actually had a lower risk of stones.
The explanation is that calcium in food binds oxalate in the gut, so less oxalate is absorbed and excreted in urine. Restricting dietary calcium may therefore increase urinary oxalate and the risk of stones, as well as harming bone health.
Dietary calcium, ideally spread across meals, adequate fluid intake and moderate salt and animal protein consumption are the cornerstones of stone prevention. People with a history of stones should follow advice from their urologist or renal team.
Supplements are a different matter: taking calcium tablets between meals may not offer the same oxalate-binding benefit. If supplements are needed, taking them with food is often suggested.
Myth 4: 'Only dairy provides calcium'
Milk, yoghurt and cheese are convenient and well-absorbed sources, but they are not the only options. People following plant-based diets can meet their needs with careful planning.
| Food | Typical portion | Approximate calcium |
|---|---|---|
| Semi-skimmed milk | 200 ml | About 240 mg |
| Cheddar cheese | 30 g | About 220 mg |
| Calcium-set tofu | 100 g | Often 200 mg or more (varies by brand) |
| Fortified plant drink | 200 ml | About 240 mg if fortified |
| Tinned sardines with bones | Half a tin | Roughly 200–300 mg |
| White bread (fortified in the UK) | 2 slices | About 80–100 mg |
In the UK, white and brown flour is fortified with calcium by law, which contributes to intake. Organic plant drinks are often unfortified, so labels are worth checking.
Spinach is a common example of a misleading source: it contains calcium, but much of it is bound to oxalate and poorly absorbed. Kale, broccoli and pak choi are better plant options.
- Spread calcium-rich foods across the day.
- Pair calcium intake with adequate vitamin D, especially from October to March in the UK.
- Check plant drink labels for fortification.
Editorial conclusions
Calcium is essential, but once needs are met more is not better, and bone strength depends on loading, vitamin D, protein and energy availability too.
Dietary calcium does not cause kidney stones and may protect against them, while supplements carry a small risk of side effects and should be used with a clear reason.
Most active adults can reach the UK target of 700 mg per day from a varied diet that includes dairy or fortified alternatives.
For related reading, our editorial team suggests articles on vitamin D during the UK winter, relative energy deficiency in sport (RED-S) and magnesium for athletes.
References
- Tai V, Leung W, Grey A, Reid IR, Bolland MJ. Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ. 2015;351:h4183.
- Bolland MJ, Leung W, Tai V, et al. Calcium intake and risk of fracture: systematic review. BMJ. 2015;351:h4580.
- Bolland MJ, Avenell A, Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010;341:c3691.
- Jackson RD, LaCroix AZ, Gass M, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354(7):669–683.
- Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med. 1993;328(12):833–838.
- Department of Health. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Report on Health and Social Subjects 41. London: HMSO; 1991.
