The calcium controversy

If you take a calcium supplement and you’re a regular walker, you might think you’re doing everything you can to prevent osteoporosis. Think again.

The two-pronged approach of adequate calcium intake and weight-bearing exercise is still a sound strategy to prevent the crippling, bone-wasting disease of osteoporosis, which affects 1.4 million Canadians. But not all calcium supplements are created equal and, as for a walking workout, that may not be enough.

First, let’s look at calcium. According to the Osteoporosis Society of Canada, people aged 50-plus need 1,500 mg of calcium daily — a challenge to get from food alone. That’s why many people take a calcium supplement. If you’re one of them, there are several reasons why you may not be absorbing the amount of calcium you think you are.

According to a growing body of research, including a 2004 study from the University of Connecticut Health Center and a University of Texas meta-analysis of 15 studies, calcium carbonate — the cheapest and most widely available calcium supplement — is not nearly as well absorbed as calcium citrate. Calcium citrate is better absorbed by 22 to 27 per cent.

What’s more, caium carbonate, which requires stomach acid for effective absorption, must be taken with a meal and may cause gas, bloating, nausea or constipation. Calcium citrate, lactate and gluconate may be taken anytime and rarely cause side effects.

“I don’t like calcium carbonate anymore,” says Susan Whiting, professor of nutrition at the University of Saskatchewan in Saskatoon and a consultant to the Osteoporosis Society. “I get this feeling of slight nausea when I take it. I take calcium citrate. It’s more expensive, but I prefer it.”

Sometimes, calcium pills don’t break down at all, meaning you’re not absorbing anything. Whole, undigested vitamin pills have reportedly been found during septic tank cleaning. If you’re unsure whether you’re digesting your calcium tablets at all, try dropping one in a small glass of vinegar. “If it doesn’t disintegrate within 15 minutes, it won’t in your belly either,” says Miriam Nelson, associate professor of nutrition at Tufts University in Massachusetts and author of Strong Women, Strong Bones (Perigree, 2001) and other books on preventing osteoporosis. Chewable or effervescent tablets or liquid calcium may increase absorption, but it’s important not to take too much calcium. A daily intake of more than 2,500 mg can cause kidney stones or even life-threatening kidney failure, says Whiting.

Coral calcium, sometimes touted as a cure-all, is nothing more than ordinary calcium carbonate from limestone. It’s not only more expensive than other types of calcium but also more likely to contain lead, a carcinogen. The Osteoporosis Society also advises against oyster shell, bone meal or dolomite, which may also contain contaminants. Calcium citrate and refined calcium carbonate have the lowest lead content.

No matter how you get your calcium, it won’t be effectively deposited in your bones without vitamin D3. This crucial nutrient comes mostly from the sun, but in northern climates — like Canada’s — it’s near impossible to get enough in winter. Research is ongoing, but Whiting says this could explain why osteoporosis rates among Canadians are much higher than in southern climes, where calcium intake is much lower. Vitamin D3 promotes calcium absorption from the usual amount of 30 per cent to up to 80 per cent. Adults over 50 need 800 IUs of vitamin D3 a day.

Note that some foods, including salt and caffeine, cause you to lose calcium. Add table salt sparingly and limit your coffee intake to no more than two mugs a day.

The Osteoporosis Society has the following suggestions when choosing a calcium supplement:

• Look for a product with DIN (Drug Identification Number), USP (United States Pharmacopoeia) or GP (General Product) numbers, which show Canadian standards have been met.
• Look for a product that lists elemental calcium.
• If you choose calcium carbonate, take it with a meal. Calcium citrate can be taken anytime.
• Limit calcium intake, whether from food or supplement, to 500 mg at one time.

But calcium alone isn’t enough to safeguard bones. Exercise is crucial, and while any exercise is better than none, some types are particularly good at building bone. According to the U.S. Centers for Disease Control and Prevention, aerobic exercise does not necessarily increase bone density. But weightlifting does, and the heavier the weights, the better.

The 2004 Bone Estrogen Strength Training (BEST) study from the University of Arizona tracked 266 formerly sedentary women ages 45 to 65. While all took 400 mg of calcium citrate twice a day, those who did a thrice-weekly exercise program focusing on six simple strength-training exercises built bone in the hip and spine, whether or not they were also taking hormone replacement therapy. While experts used to say that older people, especially women, should do many repetitions with light weights, this study found that fewer reps with heavier weights built the most bone.

Strength-training could make a difference even in women who are genetically predisposed to osteoporosis. Rosa Lawson of King City, Ont., whose mother and grandmother had osteoporosis, drank four glasses of milk daily throughout her youth. As an adult, she did regular aerobics classes and lifted weights. From age 40, Lawson’s bone density scans were always perfect. But two years ago, she joined a walking group, stopped lifting weights and did no upper-body exercises. Last year, her scan showed that from the waist down, her bones are still perfect; but in her upper spine, she has osteopenia, the precursor to osteoporosis. Lawson, 52 and not yet menopausal, says, “I think stopping the weights made the difference.”

Strength-training can be helpful in slowing the rate of bone loss in women over 50, says Sonia Bibershtein, a physical therapist with the multidisciplinary osteoporosis program at Sunnybrook and Women’s College Health Sciences Centre in Toronto. “Strength-training builds muscle, which pulls on the bone and stimulates bone growth,” she says.