Calcium
Calcium is the most abundant mineral in the human body and is best known for its role in building and maintaining bones and teeth.
Almost all of the body's calcium is stored within the skeleton, where it provides structural strength. A much smaller amount circulates through the blood and tissues, where it performs essential roles in muscle contraction, nerve signalling, blood clotting and cellular communication.
Calcium and Bone Health
Bones act as both structural tissue and a reservoir for calcium.
Bone is constantly being remodelled, with old tissue broken down and new tissue formed. Calcium forms part of the mineral matrix that gives bone its hardness and strength.
Adequate calcium intake throughout life therefore contributes to normal bone development and maintenance.
Bone health also depends on more than calcium alone. Vitamin D, magnesium, protein, vitamin K, hormones and regular weight-bearing or resistance exercise all influence how well bone is built and maintained.
Calcium, Muscles and Nerves
Calcium plays an important role in communication between nerves and muscles.
When a nerve signals a muscle to contract, calcium is released within the muscle cell and helps activate the proteins responsible for producing force.
Calcium also participates in nerve transmission and cellular signalling throughout the body.
This means maintaining adequate calcium status is important for normal movement and nervous-system function as well as skeletal health.
Calcium and Healthy Ageing
Bone mass generally reaches its peak in early adulthood before gradually declining with age.
Maintaining adequate calcium intake becomes increasingly important as we get older, particularly alongside resistance and weight-bearing exercise.
Women can experience faster bone loss during and after menopause as declining oestrogen alters normal bone remodelling.
Calcium alone cannot prevent osteoporosis, but adequate intake forms part of a wider strategy that includes vitamin D, sufficient protein, regular physical activity, avoiding smoking and appropriate medical assessment where fracture risk is elevated.
Calcium and Vitamin D
Vitamin D plays a central role in calcium absorption.
It helps the intestine absorb calcium from food and supplements and contributes to maintaining normal calcium levels within the blood.
This is why calcium and vitamin D are commonly combined in bone-health supplements.
Other nutrients, including magnesium and vitamin K, also contribute to normal bone and mineral metabolism, making overall dietary quality more important than focusing on a single nutrient in isolation.
Food Sources of Calcium
Many people can obtain a substantial proportion of their calcium through food.
Good dietary sources include:
- Milk, yoghurt and cheese
- Calcium-fortified plant milks
- Sardines and canned salmon with edible bones
- Calcium-set tofu
- Kale, bok choy and some other leafy vegetables
- Fortified foods and beverages
The amount absorbed varies between foods depending on the calcium content and other compounds within the meal.
For people who avoid dairy, checking whether plant-based alternatives are fortified with calcium can make a meaningful difference to overall intake.
Calcium Carbonate and Calcium Citrate
Two of the most common forms used in supplements are calcium carbonate and calcium citrate.
Calcium carbonate contains a relatively high proportion of elemental calcium and is generally absorbed best when taken with food.
Calcium citrate contains less elemental calcium by weight but is less dependent on stomach acid for absorption, making it useful in formulas where digestive tolerance or lower gastric acidity is a consideration.
Neither form is automatically "better" for everyone.
The most useful number on a supplement label is the amount of elemental calcium provided rather than the total weight of the calcium compound.
How Much Calcium Do We Need?
Calcium requirements vary according to age, sex and life stage.
For most adults, recommended daily intake is around 1,000 mg, with requirements increasing to around 1,200 mg for some older adults and post-menopausal women.
This total includes calcium obtained from food as well as supplements.
Larger supplemental doses are not necessarily absorbed more efficiently. Calcium absorption from supplements is generally better when individual doses provide around 500 mg or less.
For many people, supplements therefore work best as a way to fill a dietary gap rather than provide the entire day's calcium intake.
Can You Take Too Much Calcium?
More calcium is not automatically better.
High supplemental intakes can contribute to constipation, bloating or other digestive discomfort, particularly with calcium carbonate.
People with kidney disease, a history of certain kidney stones or disorders affecting calcium metabolism should seek professional guidance before using higher-dose calcium supplements.
Calcium can also interfere with the absorption of some medicines, including thyroid hormones, tetracycline and quinolone antibiotics, and bisphosphonate osteoporosis medications.
These medicines may need to be taken several hours apart from calcium supplements according to the advice of a pharmacist or prescriber.
Calcium in O2B Products
At O2B Healthy, calcium is provided most directly in O2B Calci-Mag, which combines calcium carbonate and calcium citrate to provide 200 mg of elemental calcium per capsule alongside magnesium, zinc and vitamin D3. It is also included in O2B Multi Mineral, providing 100 mg of calcium from carbonate and citrate alongside magnesium, vitamin D3, vitamin K2 and other minerals, and in O2B Multi Vitamin+ as calcium citrate. O2B Hyper Zinc also contains calcium carbonate as part of its broader vitamin, mineral and nervous-system formula. Across these products, calcium supports healthy bones and teeth, normal muscle contraction, nerve signalling and everyday mineral balance.