Calcium: A user's guide

As a physiatrist (a specialist in Physical Medicine and Rehabilitation), I see a lot of patients with musculoskeletal problems. And of all the supplements that I prescribe, I get the most questions about calcium. This is not surprising. After all, everywhere you turn these days, marketers and medical experts alike seem to be pushing calcium. And as you get older, you’re constantly reminded to get enough calcium. Store shelves teem with different brands of calcium supplements being promoted to keep your bones strong, prevent osteoporosis, and reduce the risk of fractures.

But the science behind calcium supplementation isn’t so simple. In fact, recent research seems to come up with contradictory results, further confusing our patients. Here are some of the questions I get most often from patients and my answers to them:

How much calcium should I be taking each day?

The official recommendation is 1,000 mg. a day for adults, ages 19 to 50, and 1,200 mg. for those above 50. Those amounts include calcium from food and supplements.

Is it better to get your calcium from food or from supplements?

There are studies that support the notion that it makes sense to get most of your calcium from a balanced and varied diet. On the other hand, it can be difficult to get all the calcium you need from food alone and in fact, studies show that most people do not.

How much calcium am I getting if I don’t take a supplement?

A reasonably good diet that includes some fruits and vegetables provides about 200 mg. to 300 mg. dailyand that’s without any dairy products. A cup of milk adds another 300 mg. and the typical serving of many dairy products provides 150 mg. or more (cheese lovers should go for the hard stuffit has more calcium). So a well-rounded diet with some servings of milk and dairy products puts you well into the neighborhood of 600 mg. to 800 mg. a day.

Which foods are rich in calcium?

Milk and other dairy products are the best sources of calcium. Others include fish, especially the smaller ones which are eaten with soft, edible bones such as dilis, salmon, and sardines; soybean curd or tofu (tokwa); and green leafy vegetables such as malunggay, saluyot, and mustasa.

And what about calcium supplements which type should I take?

Most calcium supplements are made with either calcium carbonate or calcium citrate. Calcium carbonate needs stomach acid to be absorbed, so if it is the source of calcium in your supplement, it’s best to take it just after a meal. Calcium citrate isn’t as dependent on stomach acid, so it can be taken any time. People taking medications that reduce stomach acidsuch as the proton-pump inhibitors (e.g. Nexium, Prevacid, Losec) or the H2 blockers (e.g. Tagamet, Zantac)should take a calcium citrate supplement because lower amounts of stomach acid mean they won’t absorb calcium carbonate properly.

The big advantage of calcium carbonate over calcium citrate is that it contains twice as much calcium. The labels on the bottles sometimes make it seem like both kinds of tablets provide the same amount of calcium, usually 500 mg. to 600 mg. But that’s the amount of calcium per “serving” and if you read the label, you’ll see that the serving size for the calcium citrate supplements is usually two tablets, but for the calcium carbonate supplements, it’s just one.

It’s a waste to double the serving size. The body can only absorb a 500- or 600-mg. dose at one time, so if you take more than that, absorption becomes inefficient. You’ll get about the same amount of calcium by taking 1,000 mg. as you would if you stuck with the 500 mg. or 600 mg. Of course, you may divide the dose and give it twice a day.

Are there any side effects?

Calcium supplements can cause gastrointestinal distress, including constipation, bloating, and flatulence. Calcium carbonate seems to trigger such symptoms more often.

Many calcium supplements include vitamin D. Why?

Vitamin D aids in the absorption of calcium, but the evidence from studies of calcium and vitamin D combinations is one of those mixed results quagmires. Part of the problem may be the vitamin D dose. Several important studies used 400 IU, and it may take double that amount of vitamin D to make a big difference in bone health. Most of the current batch of calcium-vitamin D products contains either 200 IU or 400 IU of D. There’s a school of thought that we need to ramp up our vitamin intake to 1,000 IU or more a day (Refer to this column’s article of July 27, 2010).

If I already take anti-osteoporotic drugs (Bonviva, Fosavance, Protos, Actonel, Evista), do I still have to take calcium supplements?

It is important to emphasize that those who are taking anti-osteoporotic medications should still take calcium supplements because the effectiveness of these drugs depends on ample calcium intake.

Does high calcium intake cause kidney stones?

About 80 percent of the time, kidney stones are made up of calcium, so on the surface, it makes sense that calcium intake might cause stones. But studies going back more than 10 years ago have shown just the opposite: High calcium intake, if it comes from food, makes developing a kidney stone less likely. One possible explanation is that calcium retards the absorption of oxalate, a molecule that often mixes with calcium to cause kidney stones. Oxalate is found in many plant foods, including some varieties of berries, spinach, nuts, and some grains.

Several studies have found that calcium supplements, in contrast to calcium from food, are associated with a slight risk for kidney stones. Researchers have speculated that if people take calcium pills separately from meals, or at just one meal a day (typically breakfast), then calcium may be absent from the gut much of the time and not available for oxalate-blocking duties.

Does a high intake of calcium increase the risk of developing cancer?

The good news is that studies have pretty consistently shown that people with high calcium intake and lots of dairy products in their diet are less likely to get colon cancer. Less certain are findings that suggest some protective effect for lung and breast cancers. The bad news is that a number of studies have linked calcium and dairy intake to ovarian cancer and advanced-stage prostatic cancer.

On both the good and bad news, the evidence is suggestive, not definitive, and a long way off from proof.

Will taking calcium supplements deposit calcium in my arteries?

CT scans show calcium deposits in atherosclerotic plaques in arteries, so there’s been some concern that high calcium intake may cause more calcium deposits in arteries, including those in the heart. But calcium deposits are a consequence of the inflammatory processes that produce atherosclerosis and probably have little to do with blood levels of the mineral. The way to avoid calcium deposits in your arteries is to minimize atherosclerosis, which means exercising, avoiding cigarette smoking, and controlling blood pressure, blood sugar, and cholesterol levels. And calcium may help in that regard because it seems to help lower blood pressure and cholesterol levels.

The results of a New Zealand study published in early 2008 caused some consternation because it showed that women who took calcium (1,000 mg. daily of calcium citrate) were more, not less, likely to have heart attacks and other cardiovascular problems compared with those who took placebo. But, as the researchers noted, this was a preliminary finding that might prompt more research and far from a final verdict on calcium and cardiovascular risk.

Any further tips for taking calcium supplements?

Yes, take calcium with meals, but preferably not with your multivitamin/mineral, as calcium binds with iron and zinc. Look for a calcium supplement with at least 200 IU of vitamin D per dose. Better absorbed vitamin D3 (cholecalciferol) is preferred over D2 (ergocalciferol). Added minerals, especially magnesium, are a bonus. Generics are cheaper and acceptable in quality as long as it’s a trusted brand.