Minerals Guide – CALCIUM
Calcium in which Food?
Calcium metal, abbreviated Ca, is an alkali element in Group 2 of the Periodic Table of Elements. It reacts with water exothermically to produce hydrogen gas and the strong alkali calcium hydroxide. It is the third most abundant metal in the Earth’s crust and was discovered by the Cornish chemist and inventor Humphrey Davy in 1808. Davy invented the Davy lamp and an early form of arc lamp. Think about the amount of calcium in limestone, chalk, and marble – it's very common, and our bones are mostly made of it.
In nutrition, however, we are not concerned about the metal but rather the mineral in its ionic form, Ca2+. This ion is a calcium atom stripped of two valence electrons, so it has completely different chemical properties than the reactive calcium atom.
Calcium is a crucial structural mineral in biochemistry, and we each carry about 1.2 kg of the substance in our bodies, which is far more than any other mineral. Most of it is stored in our bones as hydroxyapatite. Amazingly, 99 percent of the calcium we eat goes straight to the bones and teeth. The other 1 percent plays a role in blood clotting, nerve conduction, muscle contraction, energy production, and the immune system.
Calcium Absorption from Food
All the calcium we eat goes out of the stomach and into the small intestine or ileum. There, it needs vitamin D to get absorbed. Does that mean you might be short of calcium if you don’t get exposed to sunlight? Perhaps. However, a lack of calcium at any stage in life means that bone stores are raided, elevating the risk of osteoporosis in the future. This is why children and adolescents need plenty of calcium as their bones develop. Also, aging adults need to consume more calcium because their bones naturally start to thin.
Dietary Calcium Sources
Here’s what we know about calcium in which food. Leafy greens such as kale, collard greens, and broccoli are not only high in vitamins and minerals but also excellent sources of calcium. In fact, one cup of cooked collard greens contains 268 mg of calcium, which is about 27% of the recommended daily intake for adults. Other leafy greens like kale also contain significant amounts of calcium, making them a great addition to any diet.
Milk and dairy products, eggs, green leafy vegetables (especially broccoli), salmon (tinned or fresh with bits of bone), seeds and nuts, pulses, and calcium-fortified bread are excellent sources of the mineral. You won’t get much calcium from spinach, though, because the plant’s oxalate content reduces its bioavailability.
A pint of milk a day
To boost your calcium intake, drink an extra pint of skimmed or semi-skimmed milk each day. A pint holds about 720 mg of calcium, or half the daily requirement. Whole milk is the same but has more fat. Nevertheless, milk is an superb source of calcium because it’s easily absorbed in the gut as calcium lactate. However, there is more calcium in brassica vegetables (cabbage, broccoli, etc., than in dairy products. Indeed, 61 percent of the mineral in broccoli is absorbable compared to 32 percent of that in milk. As for other foods, about a third of the calcium in them is absorbable.
High-fiber diets, which speed the passage of food through the bowels, reduce the amount of calcium absorbed, so try to balance things. Calcium in the form of supplements is an excellent antacid, as they help to reduce the symptoms of heartburn and indigestion.
For Reducing Blood Pressure
Low calcium intake is linked with high blood pressure and stroke. Why? Because calcium is vital for blood vessel contraction and dilation. A study found that people with a high calcium intake had the lowest risk of developing hypertension. Another study found that consuming 1,200 mg of calcium daily helps reduce blood pressure.
Keeping Osteoporosis at Bay
Supplementing with 1,000—1,500 mg of calcium helps prevent bone loss in older women, a study found. Bone loss is increased during the dark season when vitamin D levels naturally plunge due to less exposure to sunlight. So, taking calcium supplementation is a good idea during late autumn and most of winter. Another study found that calcium supplementation reduces the rate of bone loss and the risk of fracture .
It was found that the most effective doses were 1,200 mg of calcium and 800 IU of vitamin D. (IU means International Units – a way of quantifying how much a mineral should have an effect on the body). Vitamin D is found in a small number of foods: oily fish – such as salmon, sardines, herring and mackerel; red meat; liver; egg yolks; fortified foods, like some fat spreads and breakfast cereals.
Calcium deficiency is widespread, with over half of adults aged 19 to 24 having less than the RNI (Reference Nutrient Intake) of 700 mg daily. (The RNI is the amount of a nutrient that is enough to ensure that the needs of nearly all a group (97.5%) are being met).  Low calcium intake levels are linked with muscle aches and pains, twitching, cramping, and spasms. They are also linked with gum disease, loose teeth, high blood pressure, and osteoporosis. So, it’s not a good idea to have a low daily calcium intake.
800 mg per day. The safe upper level for long-term supplementation is 1,500 mg per day. Calcium tablets are best taken with evening meals as calcium flux is greatest in the body at night when growth hormone is secreted. Those taking the higher doses should spread supplementation around the day. Effervescent tablets or calcium-enriched drinks help improve absorption. So now you know about calcium in which food.
1. Tang BM et al. Lancet 2007;370(9588):657-66
Synonymous terms: highest calcium foods; calcium-rich foods for bones; calcium in eggs; calcium in yogurt; calcium foods for adults