Calcium is the most abundant mineral in the human body, and about 99% of it is stored in bones and teeth. It builds strong bones in childhood and helps protect them as we age. Yet surveys show many people, especially teenagers and older women, do not get enough. In Part 6 of Vitamins and Minerals Explained, we look at calcium.
What does calcium do?
- Bones and teeth: calcium gives them structure and strength. Bones act as a calcium "bank," constantly being broken down and rebuilt.
- Muscles: calcium is needed for muscles, including the heart, to contract.
- Nerves: it helps nerves send messages.
- Blood: it helps blood clot and blood vessels contract and relax.
- Hormones: it helps release hormones and enzymes.
The body tightly controls the level of calcium in the blood. If you do not get enough from food, it takes calcium from your bones, which can weaken them over time.
How much calcium do you need?
According to the US National Institutes of Health (NIH):
| Age group | Recommended daily amount |
|---|---|
| Birth to 6 months | 200 mg |
| 7–12 months | 260 mg |
| 1–3 years | 700 mg |
| 4–8 years | 1,000 mg |
| 9–18 years | 1,300 mg |
| Adults 19–50 | 1,000 mg |
| Men 51–70 | 1,000 mg |
| Women 51–70 | 1,200 mg |
| Adults 71+ | 1,200 mg |
| Pregnancy and breastfeeding (19+) | 1,000 mg |
The teenage years are especially important because this is when most bone mass is built. Women over 50 need more because bone loss speeds up after menopause.
Best food sources of calcium
Dairy products are the richest and most common sources, but many non-dairy foods also provide calcium. The table below shows top sources from the NIH (the US Daily Value is 1,300 mg).
| Food | Serving | Calcium | % DV |
|---|---|---|---|
| Plain low-fat yoghurt | 8 oz (227 g) | 415 mg | 32% |
| Calcium-fortified orange juice | 1 cup | 349 mg | 27% |
| Fruit yoghurt, low-fat | 8 oz | 344 mg | 27% |
| Mozzarella, part skim | 1.5 oz | 333 mg | 26% |
| Sardines, canned with bones | 3 oz | 325 mg | 25% |
| Milk, nonfat | 1 cup | 299 mg | 23% |
| Soy milk, calcium-fortified | 1 cup | 299 mg | 23% |
| Milk, whole | 1 cup | 276 mg | 21% |
| Firm tofu made with calcium sulfate | ½ cup | 253 mg | 19% |
| Pink salmon, canned with bones | 3 oz | 181 mg | 14% |
| Cottage cheese, 1% | 1 cup | 138 mg | 11% |
| Soft tofu made with calcium sulfate | ½ cup | 138 mg | 11% |
Other sources include kale, bok choy, broccoli, almonds, sesame seeds, fortified cereals and calcium-set tofu. Note that spinach contains calcium but very little is absorbed: the NIH notes only about 5%, compared with about 30% from dairy.
How to absorb more calcium
- Vitamin D: it is essential for absorbing calcium (see Part 1).
- Spread it out: the body absorbs calcium best in smaller amounts. According to the NIH, absorption from supplements is highest at doses of 500 mg or less, so larger amounts are best split through the day.
- Oxalates and phytates: compounds in spinach, rhubarb, beans and whole grains can reduce absorption from those foods.
Who is at risk of not getting enough?
- Postmenopausal women, because falling oestrogen speeds up bone loss. The NIH notes about 30% of postmenopausal women in the US and Europe have osteoporosis.
- Children and teenagers: NIH survey data show 49% of children aged 4 to 18 get less calcium than needed.
- People who avoid dairy, including those with lactose intolerance, milk allergy or vegan diets, unless they eat fortified foods.
- Older adults, who absorb less calcium.
What happens if you do not get enough?
Low calcium intake usually causes no symptoms in the short term because the body takes calcium from bones. Over years, this can lead to:
- Osteopenia and osteoporosis: thinning, fragile bones that break easily.
- Rickets and osteomalacia: soft bones, though these are more often caused by low vitamin D.
Very low blood calcium, called hypocalcaemia, is usually caused by medical problems rather than diet. Symptoms can include numbness or tingling around the mouth and in the hands and feet, and muscle spasms. Severe cases can cause seizures and heart problems and need urgent care.
Calcium supplements
The two main forms are:
| Form | Elemental calcium | How to take it |
|---|---|---|
| Calcium carbonate | 40% | Best absorbed with food; may cause more gas and bloating |
| Calcium citrate | 21% | Can be taken with or without food; often better for people with low stomach acid or taking acid-reducing medicines |
Check the label for "elemental calcium," which is the actual amount of calcium you get. Many people only need a small supplement, if any, once their diet is taken into account.
Can you have too much calcium?
The NIH sets these daily upper limits from food and supplements combined:
| Age | Upper limit |
|---|---|
| 1–8 years | 2,500 mg |
| 9–18 years | 3,000 mg |
| 19–50 years | 2,500 mg |
| 51 years and older | 2,000 mg |
Too much calcium can cause constipation and may interfere with absorption of iron and zinc. Very high blood calcium can cause kidney problems and heart rhythm issues. Some studies have linked calcium supplements with kidney stones, though later reviews have produced mixed results.
What does the research say?
Bones and fractures
Calcium with vitamin D is a standard part of osteoporosis prevention and treatment. One analysis of trials in adults over 50 found calcium plus vitamin D reduced total fractures by 15% and hip fractures by 30%, but other reviews found no clear benefit, especially at lower doses. Overall, adequate calcium is important, but supplements are not a guarantee against fractures; exercise, vitamin D and fall prevention matter too.
Heart health
Some studies raised concerns that calcium supplements might slightly increase cardiovascular risk. Expert panels reviewing the evidence concluded that calcium from food and supplements within recommended limits does not appear to increase or decrease heart disease risk. Getting calcium from food is generally preferred.
Pregnancy
For pregnant women with low calcium intake, supplements of 1,500 to 2,000 mg a day may reduce the risk of preeclampsia, a dangerous rise in blood pressure, and the World Health Organization recommends this for such groups.
Medicine interactions
- Levothyroxine (thyroid medicine): calcium carbonate can reduce absorption; take them at least four hours apart.
- Some antibiotics (quinolones): take two hours before or after calcium.
- Certain HIV medicines (dolutegravir) need to be separated from calcium.
- Lithium: combined use may increase the risk of high blood calcium.
Practical tips
- Aim for two to three servings of dairy or fortified alternatives a day.
- If you avoid dairy, choose calcium-fortified plant milks, calcium-set tofu, canned fish with bones and leafy greens like kale.
- Get enough vitamin D and do weight-bearing exercise for strong bones.
- If you take a supplement, split doses above 500 mg and take carbonate with food.
- Do not exceed the upper limit without medical advice.
Frequently asked questions
Is dairy the only good source of calcium?
No. Fortified plant milks, calcium-set tofu, canned fish with bones, almonds and leafy greens such as kale and bok choy are good alternatives.
Should I take calcium at night?
Timing is flexible. Calcium carbonate is best with meals; citrate can be taken any time.
Do men need calcium supplements?
Most men can get enough from food. Supplements are mainly considered when diet is inadequate or for specific medical reasons.
In Part 7, we look at zinc and its role in immunity, wound healing and taste.
Sources
- NIH Office of Dietary Supplements – Calcium (health professional fact sheet)
- NIH Office of Dietary Supplements – Calcium (consumer fact sheet)
Vitamins and Minerals Explained: the full series
- Part 1: Vitamin D
- Part 2: Vitamin B12
- Part 3: Iron
- Part 4: Magnesium
- Part 5: Vitamin C
- Part 6: Calcium (you are here)
- Part 7: Zinc
- Part 8: Omega-3 Fatty Acids
- Part 9: Folate and Folic Acid
- Part 10: Vitamin A
- Part 11: Vitamin E
- Part 12: Vitamin K
- Part 13: Potassium
- Part 14: Iodine
- Part 15: Biotin
- Part 16: Do You Need Supplements?
This article is for general information only and is not medical advice. Recommended amounts shown are US figures from the NIH Office of Dietary Supplements; guidance in other countries may differ slightly. Talk to a doctor or pharmacist before starting supplements, especially if you are pregnant, take medicines or have a health condition.
