Calcium is often cited as a bone-healthy, heart-healthy supplement.
Calcium supplements are commonly prescribed for prevention and treatment of osteoporosis, a condition in which bone tissue calcium has been depleted and can result in fracture.
Health advice often includes admonitions to drink plenty of milk to ensure adequate calcium intake. Studies have suggested that greater calcium intake also reduces risk for colon cancer and high blood pressure.
Several dozen major studies over the past 20 years have documented the value of calcium supplementation for bone health. Women who take calcium supplements enjoy less osteopenia and osteoporosis (both representing loss of bone calcium), as well as fewer bone fractures. That much is true.
But what happens to heart health when a woman takes calcium supplements at the previously recommended dosages of, say, 1200 mg per day?
A 2008 University of Auckland study suggested that taking 1000 mg of calcium (Citrical, a brand of calcium citrate) more than doubled risk for heart attack.
Uh oh. Have there been confirming studies? Unfortunately, the data are scant, with almost no studies that look specifically at calcium intake and heart attack risk. However, a similar phenomenon has been observed in males at a calcium dose of 1200 mg per day (323 men, 1200 mg calcium; 5 heart attacks in calcium group, zero in placebo group.) Several others studies, though designed to examine bone measures and not heart attack, did suggest a trend towards increased heart attack in participants taking calcium.
So what should a woman do? Is calcium supplementation at the generally recommended dose of 1200 mg per day advisable for bone health? Or, will greater risk for heart attack result?
That issue is just starting to be explored. But there's an added twist: Our new appreciation for the value of vitamin D may have changed the situation.
Women who take higher doses of vitamin D than the (absurdly low!) current Recommended Daily Allowance (RDA) of 400 units, or¾even better¾try to maintain healthy blood levels of vitamin D, double, triple, or quadruple intestinal calcium absorption. Whereas a vitamin D deficient woman absorbs only 10 mg of every 100 mg taken, a vitamin D replenished woman absorbs 40 mg or more. Calcium intake may no longer be as important as once thought.
In other words, the years of studies force-feeding women calcium supplements may no longer be relevant in an age in which we've come to appreciate the profound implications of vitamin D deficiency and the enormous benefits of correcting deficiency, including enhanced intestinal absorption of calcium. With supplementation of vitamin D at truly healthy doses, your intestinal tract becomes a magnet for calcium, pulling it out of even broccoli, spinach, and other foods ordinarily not felt to be substantial sources. Vitamin D by itself exerts powerful effects on increasing bone density, regardless of calcium supplementation.
Calcium is making its way into numerous food products, like orange juice (up to 500 mg per 8 oz serving) and bread. Many people take calcium supplements. If you have made the effort to normalize the vitamin D levels in your system, are you increasing your risk for heart attack?
My personal view is that, given our new appreciation for the impact of vitamin D on calcium absorption, we should reduce our calcium intake to no more than 600 mg per day. Of course, this requires confirmation in a new round of studies examining people who take "modern" doses of vitamin D of 2000, 4000, 8000, or more units to restore blood levels to normal.
Be sure to check out Dr. Davis' last post on bone health for more perspective.