Calcium

Calcium is the most abundant mineral in the body, and almost all of it (about 99 per cent) is in bones and teeth. The other 1 per cent is in blood, soft tissue, and the fluid around cells, where it plays a sharply controlled role in blood clotting, muscle contraction, nerve signalling, and the release of hormones.

The body keeps blood calcium in a very tight range. When dietary calcium runs low, the body pulls it out of bone to maintain blood levels. Over time, a habit of low intake plus low vitamin D status weakens bone strength, raising the risk of osteoporosis and fractures in later life. Bone is laid down most rapidly during childhood and adolescence and is largely set by the late twenties; the calcium and vitamin D you take in across childhood and the teen years sets the maximum bone density you carry into adult life. After about age 50, particularly in women after the menopause, bone loss can accelerate, and adequate calcium plus vitamin D plus weight-bearing exercise are the standing public health advice.

You do not have to eat dairy to meet the calcium reference. Tinned sardines and tinned salmon (with the soft bones eaten), tofu set with a calcium salt, fortified plant milks, fortified breakfast cereals and fortified white bread, dark leafy greens such as kale and watercress, tahini, and pulses all carry calcium. The food table below ranks the best practical UK sources, dairy and non-dairy together.

Values per 100g come from USDA SR Legacy and McCance and Widdowson 7th edition; the site's food entries currently store macros only. Percentages of the adult RNI use 700mg as the basis.

Practical: a small glass of milk (or fortified plant milk) with breakfast, a 30g matchbox of cheese with lunch, a yoghurt pot, and a portion of greens delivers the adult target without thinking about it. A vegan version: 200ml fortified plant milk, two slices of fortified bread, a tablespoon of tahini, and a portion of kale gets to roughly the same place.

Spinach is calcium-rich but the calcium in spinach is bound to oxalate, so much of it is not absorbed. Kale, broccoli, and watercress have low oxalate and the calcium in them absorbs well.

UK Reference Nutrient Intake (RNI) for calcium is set by SACN (1991 Dietary Reference Values).

Why the teen years are different: bone is being laid down rapidly and the framework that carries someone through their adult life is being set. Adolescent boys' bones, on average, get a bit bigger than girls', which is why the RNI splits.

Mild low calcium intake does not usually cause obvious symptoms in the short term. The body protects blood calcium by pulling from bone, so the long-term consequence sits in the bones rather than in noticeable day-to-day symptoms. Real low blood calcium (hypocalcaemia) is uncommon and usually has a medical cause (vitamin D deficiency, parathyroid problems, kidney disease, some medications).

Signs of clinical low blood calcium can include:

• Muscle cramps, twitches, or spasms
• Numbness or tingling in fingers, toes, or around the mouth
• Brittle nails
• Dry skin
• Persistent tiredness
• An irregular heartbeat in severe cases

The bigger UK story is dietary shortfall over years, which sets bone density lower than it could be and raises the risk of osteoporosis and fractures in later life.

Who is at higher risk in the UK

• People who do not eat dairy and have not actively replaced it with calcium-rich non-dairy options. Vegans, people with lactose intolerance, and people who simply do not drink milk.
• Postmenopausal women. Bone loss accelerates in the years after the menopause.
• Adults aged 65 and over. Reduced absorption and lower vitamin D status both play in.
• People with low vitamin D status. Calcium needs vitamin D to be absorbed, and vitamin D is low in most UK adults in autumn and winter.
• People with coeliac disease, inflammatory bowel disease, or chronic kidney disease.
• People who restrict food intake severely for any reason.
• People on long-term corticosteroids (which can reduce calcium absorption and increase bone loss).

If you have symptoms or a known risk factor for osteoporosis, your GP can arrange bone density scanning (DEXA) and check calcium and vitamin D levels. This page is reference information, not medical advice.

Calcium from food is not a realistic risk for healthy people. The risk is from very high doses of supplements, particularly when combined.

NHS supplement guidance: taking 1,500mg or less a day of calcium from supplements is unlikely to cause any harm.

Side effects from supplement doses above this range can include:

• Stomach pain
• Diarrhoea
• Constipation

Very high long-term intake from supplements has been linked in some studies to kidney stones and to a possible increase in cardiovascular risk; the evidence is mixed and the standing UK advice is to stay at or below 1,500mg per day from supplements unless directed otherwise by a clinician.

People with kidney stones, parathyroid conditions, or kidney disease need personalised advice, not the population guidance.

Most UK adults can meet 700mg from food across a varied diet, with or without dairy. Targeted supplementation is used in specific situations.

When a calcium supplement is sensible (ideally with GP or dietitian advice):

• Confirmed osteoporosis or low bone density on DEXA.
• Postmenopausal women not eating much calcium-rich food.
• People taking long-term corticosteroids.
• People with coeliac disease, inflammatory bowel disease, or kidney disease, on personalised advice.
• People whose diet is genuinely low (a quick way to estimate is to count the dairy or fortified-non-dairy servings in a typical week).

Pair with vitamin D: calcium absorbs more efficiently when vitamin D status is adequate, which for UK adults from October to March means a 10ug daily vitamin D supplement. See Vitamin D for the full guidance.

Practical choices: calcium carbonate is the most common UK form and is best taken with food; calcium citrate is easier on the stomach and can be taken any time. Both work.

Children: calcium supplements at adult doses are not recommended for children unless prescribed. Aim for the SACN child RNIs through food and Healthy Start fortified products.

• The vitamin D pairing: Vitamin D is needed to absorb dietary calcium. The two recommendations stand together.
• UK official position in practice: The Eatwell Guide groups dairy and dairy alternatives as one third of a balanced plate.
• Non-dairy and vegan calcium: Plant-based eating covers calcium for people not eating dairy.
• Best food sources: Milk, Cheddar, Plain yoghurt, Kale, Watercress, Tahini, Salmon (the tinned-with-bones form).

• NHS. Vitamins and minerals: Calcium. nhs.uk/conditions/vitamins-and-minerals/calcium. Adult RNI and supplement guidance.
• SACN. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Department of Health Report 41 (1991). Source of the age-banded RNIs.
• NHS. Osteoporosis. Background to bone density, risk factors, and DEXA scanning.
• Public Health England. McCance and Widdowson's The Composition of Foods, 7th summary edition (2015).
• USDA Agricultural Research Service. FoodData Central, SR Legacy release. fdc.nal.usda.gov.

This page is reference information for UK shoppers. It is not medical advice. People with osteoporosis, kidney conditions, or parathyroid disorders should follow personalised advice from their GP or specialist team.