| Calcium Supplements: Healthy bones . . . Sick heart?|
TRACK YOUR PLAQUE
By Dr Davis
While conventional health information encourages calcium supplementation for bone health, emerging data suggest that calcium may also increase cardiovascular risk. Are we forced to make a choice: bone health vs. heart health?
Calcium is making its way into numerous food products, like orange juice, breakfast cereals, and bread. Orange juice, in particular, has been a food manufacturer's favorite for calcium supplementation, containing as much as 500 mg per 8 oz serving. Calcium is often spotlighted as a bone-healthy, heart-healthy supplement.
Calcium supplements are commonly prescribed to prevent or treat osteopenia and osteoporosis, conditions in which bone calcium has been depleted. When severe, loss of bone calcium can result in fracture (e.g., hip fractures). Health advice often includes admonitions to drink plenty of milk to ensure adequate calcium intake. Studies have suggested that greater calcium intake may reduce 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, as well as fewer bone fractures. That much is true.
What if calcium goes where it doesn't belong?
But what happens to heart health when a man or woman takes calcium supplements at the recommended dosage of 1200 mg per day (elemental calcium; recommendation for adults over 50)? After all, calcium is the unwanted material we measure with heart scans, an important component of atherosclerotic plaque.
The tides of thinking about calcium may be shifting. A 2008 University of Auckland study suggested that taking 1000 mg of (elemental, or the actual calcium component) calcium more than doubled risk for heart attack (Bolland MJ et al 2008). 732 women received calcium supplementation as Citrical, a brand of calcium citrate; 730 women received placebo over a 5-year period. 31 women (4.2%) in the calcium group suffered heart attacks, compared to 14 (1.9%) in the placebo group. In the group receiving calcium, the relative risk compared to the placebo group (RR, i.e., risk compared to another group) for heart attack was 2.24; RR 1.59 for transient ischemic attack ("ministroke"), RR 4.04 for sudden death; RR 1.66 for the combination of heart attack, stroke, or sudden death. The figure shows the divergence of heart attack (myocardial infarction) of calcium vs. placebo over the 5-year period, beginning at about 2 ½ years.
From Bolland MJ et al BMJ 2008.
Uh oh. Have there been confirming studies?
A similar phenomenon has been observed in males in a study performed by the same group at the University of Auckland. 323 men were given 1200 mg (elemental) calcium, 600 mg calcium, or placebo, then observed for two years. While bone mineral density increased by 1.5% in the group receiving 1200 mg calcium (no bone mineral density increase in the 600 mg group or placebo), there were a total of 5 cardiovascular events - heart attack, cardiovascular death, and angina or chest pain - in the groups taking calcium (600 or 1200 mg), none in the 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:
* The RECORD Trial: 5292 participants given 1000 mg calcium (elemental), 800 units vitamin D; death rate in calcium group 18.5%, death rate in placebo group 16.3% (Grant AM et al 2005).
* In an Australian study, heart disease was diagnosed in 56 patients (7.7%) in the calcium group and in 51 patients (7.0%) in the placebo group, with a relative risk of heart disease for the calcium compared with placebo group of 1.12 (Prince RL et al 2006).
* An analysis of the Women's Health Initiative trial of 36,282 females assigned to calcium, 1000 mg per day (elemental), and vitamin D, 400 units per day, suggested a trend towards increased cardiovascular events (myocardial infarction, cardiovascular death, bypass surgery or angioplasty) with a relative risk of 1.08 in participants taking calcium and D. (Hsia J et al 2007)
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?
But wait - there's an added twist: Our new appreciation for the value of vitamin D may further change the situation.
Vitamin D: Deal breaker
Unlike the relatively minor doses of vitamin D used in the studies cited above, what happens when doses sufficient to substantially increase blood levels of 25-hydroxy vitamin D are taken?
People who take higher doses of vitamin D than the (absurdly low!) current Recommended Daily Allowance (RDA) of 400 units, or - even better - try to maintain healthy blood levels of vitamin D, will double, triple, or quadruple intestinal calcium absorption. Whereas a vitamin D deficient woman absorbs only 10 mg of every 100 mg of calcium taken, a vitamin D replenished woman absorbs 40 mg or more. Calcium intake may no longer be as important as once thought.
"Based on newly emerging data regarding calcium supplementation, and recommendations for increased vitamin D intake, the current recommendations for calcium intake in postmenopausal women may be unnecessarily high."
Current Research and Medical Opinion
Expert Roundtable Discussion, 2008
In other words, the years of studies force-feeding participants 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. Enhanced intestinal absorption of calcium alone changes the equation considerably. With supplementation of vitamin D at truly healthy doses, the intestinal tract becomes a magnet for calcium, pulling it out of broccoli, spinach, and other foods ordinarily not felt to be substantial sources.
Vitamin D by itself may improve bone health, with or without calcium supplementation. An Australian study showed decreased calcium turnover in women taking 1000 units vitamin D with calcium, 1200 mg per day, compared with calcium alone (Zhu K et al 2007). Unfortunately, in virtually all other studies, the effects of vitamin D are inseparable from that of calcium. It is therefore not possible, given current knowledge, to say with absolute confidence that vitamin D is sufficient to improve bone health without calcium supplementation.
Many people take calcium supplements. If you have made the effort to normalize vitamin D levels in your system, are you increasing your risk for heart attack? If there is indeed a trend towards greater risk for cardiovascular disease with calcium doses of 1200 mg per day when take with low-dose vitamin D, what happens at with higher vitamin D doses? It may prove to be an unhealthy combination.
My 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 if vitamin D levels have been increased with supplementation. This requires confirmation in a new round of studies examining bone density in people who take "modern" doses of vitamin D of 2000, 4000, 8000, or more units to restore vitamin D blood levels to normal. Such data are not yet available.
It's also worth mentioning that osteoporosis prevention or treatment does not have to involve high doses of calcium nor drugs like Boniva® or Fosamax®. Instead, a program of vitamin D to normalize blood levels, vitamin K2 supplementation, magnesium, and possibly DHEA and strontium can be combined for a very powerful bone density-increasing program.
Until we obtain clarification on the cardiovascular effects of calcium, 1200 mg per day, when taken with vitamin D, the Track Your Plaque approach is to include no more than 600 mg per day of calcium (elemental) in supplement form. Priority is given to vitamin D supplementation sufficient to achieve a blood level of 25-hydroxy vitamin D of 60-70 ng/ml.