Vitamins C & D increase the absorption of calcium, protecting our bones.

What does calcium do in the body? How much calcium per day?

Calcium is the most abundant mineral in the body. It’s stored mainly in bones and teeth. About 99% of the body’s calcium is stored there! Moreover, the calcium in bones is used to keep steady amounts of calcium in the blood and muscle. The body constantly regulates concentrations of calcium in the serum.

For increased calcium absorption, boost your daily vitamin C and vitamin D intake, and avoid excess consumption of caffeine, salt and alcohol.

What does calcium do in the body?

Calcium is important for many functions of the body. In fact, calcium has a key role to:

  • vascular contraction,
  • the dilatation of blood vessels,
  • muscle function,
  • nerve transmission,
  • signaling between cellular,
  • hormonal secretion,
  • blood clotting,
  • muscle contraction,
  • oocyte activation,
  • have normal heartbeat

How much calcium do I need a day?

Daily calcium intake demands are different depending on age and sex. The daily recommended calcium intake is (1).

0–6 months200 mg200 mg
7–12 months260 mg260 mg
1–3 years700 mg700 mg
4–8 years1,000 mg1,000 mg
9–13 years1,300 mg1,300 mg
14–18 years1,300 mg1,300 mg1,300 mg1,300 mg
19–50 years1,000 mg1,000 mg1,000 mg1,000 mg
51–70 years1,000 mg1,200 mg
71+ years1,200 mg1,200 mg

As you can see, most people should consume up to 1,300 mg of calcium daily. Higher doses may cause side effects.

Bioavailability of calcium

According to a report of the National Academy Press, we absorb only about 30% of the calcium from foods. Calcium absorption percentage depends on the type of food, though.

Dairy is a good dietary source of calcium. We absorb about 30% of them.

The same stands for fortified foods. So, we absorb about 30% of calcium from fortified orange juice, soy milk, or tofu.

But, we can absorb up to 60% of calcium coming from plant-based sources, such as kale, broccoli, or bok choy.

Certain foods may inhibit calcium absorption

On the other hand, healthy foods, such as beans, may inhibit calcium bioavailability. They contain phytochemicals that bind to calcium, preventing its absorption. For instance, phytic acid and oxalic acid are compounds that bind to calcium.

Foods rich in oxalic acid

The richest food in oxalic acid is spinach. A great alternative to spinach is kale. Kale is a dark leafy vegetable, rich in health-promoting phytochemicals, but low in oxalates.

Other oxalic acid-rich foods are collard greens, beet greens, sweet potatoes, rhubarb, and legumes.

Foods rich in phytic acid

Common foods rich in phytic acid are cereals, legumes, and nuts.

Phytic acid inhibits the absorption of minerals, such as calcium.

On the other hand, foods rich in phytates (phytic acid) can be important in the prevention of bone mineral density loss. Postmenopausal women who consume many phytate-rich foods can benefit the most (4).

Usually, foods rich in phytic acid are also rich in fiber. Whole-grain products, beans, seeds, nuts, and soy both good sources of phytic acid and fiber.

More calcium, less absorption

The more calcium we consume, the less we absorb. In other words, as calcium intake increases, the efficiency of absorption decreases.

Scientists have reported that the absorption of calcium can range from 60% to less than 30%. 60% at very low calcium intake. Less than 30% at a high intake.

That’s our body’s defensive mechanism, in order to avoid calcium deficiency as well as calcium toxicity.

Absorption decreases with age

Another factor for calcium absorption is age. As we get older, we absorb calcium less efficiently.

For instance, children absorb 60% of calcium. Their calcium needs are greater than adults. They need it for bone growth.

On the other hand, adults absorb about 20% of calcium.

Only, pregnant women absorb calcium more efficiently. They also have extra calcium needs.

How can you increase calcium absorption?

Actually, there are many factors that can inhibit calcium absorption.

Decrease salt intake

If you have osteoporosis or calcium deficiency, maybe it’s a good practice to cut down on salt. High sodium intake increases the losses of calcium by urine.

Foods with vitamin C enhance calcium absorption

According to a study, published by the American Society for Bone and Mineral Research, vitamin C intake may have a beneficial role in levels of bone mineral density. Scientists took data from 994 women. Women who took vitamin C had the best results. Postmenopausal women benefited the most.

But how much vitamin C should you take? Scientists couldn’t tell. Maybe 1,000 mg of vitamin C a day is a more than enough. Above all, we should start consuming a wide variety of foods rich in vitamin C.

Vitamin D increases calcium absorption

Calcium absorption is improved with vitamin D.

Vitamin D is produced by the skin when exposed to sunlight.

Many studies have shown that supplementation with both calcium and vitamin D has beneficial effects. Calcium and vitamin D can reduce fractures in the elderly.

Contrary, elderly people who don’t consume adequate amounts of calcium and have low vitamin D levels have higher risk of developing osteoporosis.

According to a study, vitamin D supplementation of 700 – 800 IU daily can reduce the risk of hip fractures in elderly people. Lower dose didn’t have any benefits. Scientists didn’t find fracture prevention when people consumed 400 IU of vitamin D per day (5).

Seems sunlight and vitamin D supplements are the only vital solutions for adequate amounts of vitamin D intake. We can’t depend on food (7).

Soak, rinse, cook

Cooking vegetables and soaking beans is a good practice if you want to increase calcium absorption. The compounds that bind to calcium, inhibiting its absorption, are water-soluble. We can reduce them by soaking and cooking.

Actually, beans are particularly high in calcium. Eat them regularly to boost calcium intake.

The best method is steaming. Steaming doesn’t leach nutrients into the water, while is reduces oxalate content up to 53% (1).

Boiling has better results, though. Boiling reduces oxalate content up to 87%. But, nutrients are leaching into the water.

Avoid excess alcohol intake

Moreover, we should avoid excess alcohol intake, as it reduces calcium absorption.

Also, alcohol inhibits the conversion of vitamin D to its active form. As mentioned, vitamin D is vital for calcium absorption.

1-2 glasses of red wine are enough. Actually, red wine can help you sleep and lose weight.

Caffeine may prevent calcium absorption

Caffeine may be harmful for calcium absorption. High amounts of caffeine increase calcium excretion. Also, they reduce calcium absorption.

Low consumption of caffeine has no negative effects, though. You can have one cup of coffee or two cups of tea daily.


  1. NCBI: Effect of different cooking methods on vegetable oxalate content.
  2. Pubmed: Mediterranean Way of Drinking and Longevity.
  3. A further study of oxalate bioavailability in foods.
  4. Reumatologia-Clinica: The influence of consumption of phytate on the bone mass in postmenopausal women of Mallorca
  5. Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials.
  6. 2014: Milk Consumption During Teenage Years and Risk of Hip Fractures in Older Adults