Boning up on calcium
Calcium is the fifth most abundant element (by mass) on Earth and the fifth-most abundant dissolved ion in seawater, following sodium, chloride, magnesium and sulfate.
The human body, on the other hand, is an entirely different matter.
To hear some nutritionists and supplement companies tell it, people aren’t getting enough calcium in their diet, especially women. The federal government recommends women and men younger than 50 consume 1,000 milligrams of calcium per day. The recommendation increases after that, rising to 1,200 milligrams for post-menopausal women and men after age 70.
Calcium, of course, is a key component in building strong, dense bones in childhood and maintaining them throughout life. Roughly 99 percent of the body’s calcium supply is stored in bones and teeth, with the remainder used for functions like neurotransmitter release and muscle contractions.
The mineral is particularly vital to women after menopause when the drop in estrogen precipitates bone loss and the possibility of osteoporosis—a thinning and loss of bone tissue over time, which makes bones more vulnerable to fractures and breaks. Researchers estimate that about one in five American women over the age of 50 has osteoporosis; about half of all women over the age of 50 will have a fracture of the hip, wrist or vertebra due to osteoporosis. (The scanning electron micrograph above, courtesy of Alan Boyd, University College London, depicts a severely hollowed out, osteoporotic bone.)
There are, however, health concerns associated with getting too much calcium.
First, the extra calcium can build up in the bloodstream and cause painful stones when excreted through the kidneys in urine.
More recently, some studies have suggested that excess calcium causes coronary arteries to harden in susceptible individuals, and may precipitate heart attacks.
So perhaps think twice about taking a calcium supplement, especially if you already enjoy a calcium-rich diet. Dairy products are the best source, of course: A single glass of milk has 300milligrams of calcium, a couple ounces of cheese has 200 to 300 mg. That’s roughly half of the daily recommendation for most people right there. Non-dairy sources of calcium include broccoli, oranges, salmon and fortified cereals, which also contain added vitamin D, which is needed to help the body absorb calcium.
