Avoiding the fracture zone.

Q. How did you decide that Americans need more calcium?

A: We looked at three lines of evidence. One was balance studies, where you see how much calcium people need to consume so that they're not losing more than they're taking in.

Second, we used bone scans to measure how much mineral is being laid down in the bone. Since bone is 32 percent calcium, you can calculate how much calcium is being laid down. Then you correct for calcium lost in urine and sweat and for what percent is absorbed from food. You add all those factors up and you come up with an estimate.

The third line of evidence was clinical trials where people were randomly assigned to get one of two different calcium intakes.

Q. What do the clinical trials show?

A: We have two remarkable studies done on older people. In the U.S., nearly 400 people aged 65 or older got either 500 mg of calcium plus 700 IU of vitamin D a day or a lookalike but inactive placebo for three years. In France, roughly 3,000 people aged 69 to 106 got either a placebo or 1,200 mg of calcium and 800 IU of vitamin D a day for a year and a half. Both studies showed less bone loss--and fewer fractures--with the supplements.

Q. What about trials of calcium alone?

A: Three smaller trials have found fewer fractures in older women taking 800 mg to 1,200 mg of calcium a day for 18 months to four years. So five out of five trials that have counted the number of fractures show fewer fractures with calcium.

Q. Some people think that calcium doesn't matter because a large study of nurses found no link with fractures.

A: In the Nurses' Health Study, researchers estimated the calcium intakes of nearly 80,000 women and waited to see if that predicted their risk of fractures. So the results depend on how accurate the estimates were.

Also, the nurses were younger than the people in the clinical trials. So there weren't enough of them in the fracture-risk zone. We don't think of fractures occurring until women are older than 65, and not too many of the nurses were in that age group. The age range was about 45 to 70.

Q. Aren't there countries with lower calcium intakes and less osteoporosis than the U.S.?

A: Yes. One example is China. But you can't make interracial and intercountry comparisons because other factors--like genetics, weight--bearing exercise, exposure to sunlight, and other nutritional factors-also influence rates of osteoporosis. Calcium isn't the only factor to predict bone mass.

For example, in China many more men and women are in the labor work force than in developed countries like the U.S. So the Chinese have more physical activity that protects against osteoporosis.

And genes give some populations greater or lesser bone mass. Genes also affect bone architecture. Some populations--like the Japanese--have a hip structure that has less propensity to fracture even at a lower bone mineral density.

Q. Do countries differ in other ways?

A: Yes. Exposure to sunlight is the most important source of vitamin D for most people, and vitamin D plays a pivotal role in enabling the body to absorb and use calcium.

You can't compare osteoporosis rates in Thailand and northern Canada, for example, because vitamin D status may be better in tropical countries than in northern countries where people are exposed to less ultraviolet light from the sun.

Q. What are the other nutritional factors?

A: Higher levels of protein, sodium, and caffeine have all been associated with a higher excretion of calcium in the urine, so they may increase the risk of osteoporosis in the U.S.

Caffeine and protein have a greater impact when calcium intake is marginal. In other words, if you consume less than 800 mg of calcium a day, two or more cups of coffee may tip you over into negative calcium balance--that is, where you're losing more calcium than you're taking in.

Q: So people who consume less protein, sodium, and caffeine than most Americans may need less calcium?

A: They may. But at the calcium intakes we recommend, caffeine, sodium, and protein have only minimal influence.

Q. How much difference does protein make?

A: The Recommended Dietary Allowance (RDA) for protein is 50 grams a day for women and 65 grams a day for men. Each gram of protein raises calcium excretion by 1 to 1.5 mg. So if a woman consumed 65 grams of protein a day--which is typical--she would lose an extra 15 to 23 mg of calcium a day.

Q: How about sodium?

A: You lose 10 mg of calcium for every 500 mg of sodium. So if you eat, say, 4,400 mg of sodium a day instead of the recommended 2,400 mg, you'd lose an extra 40 mg of calcium.

Q. Does estrogen prevent osteoporosis more than calcium does?

A: Yes. Women lose a significant amount of bone right after menopause. Taking estrogen as hormone replacement therapy is the most effective way to prevent that bone loss.

Q: Do women who take estrogen need calcium?

A: Yes. Women seem to need the same amount of calcium whether they take estrogen or not. Estrogen prevents bone loss and prompts the body to lay down calcium in the bone. But there's not enough to lay down if you don't get enough calcium.

Q: That's after menopause. Why do premenopausal women need calcium?

A: It looks like you achieve your peak bone mass in your late teen years, though you might gain slightly more in your twenties. So you want to maximize your exercise and diet to build as much bone mass as possible during that time.

From then on until you're post-menopausal, you're maintaining the skeleton. Like the protein in muscle bone mineral isn't static. It's always turning over, so you have to replace it. During those years, you need less than when you're young or very old, but if you had too little calcium or not enough exercise, you would lose bone.

Q: Is osteoporosis only a woman's problem?

A: No. A lot of men develop osteoporosis later in life. Some of the clinical studies done in the greater-than-70 age group include both men and women.

Men have a lower incidence of osteoporosis, because they start out with more bone mass. And in women, a major decline in bone occurs immediately following menopause. Men don't have that trigger, so it's a more gradual loss.

RELATED ARTICLE: CRAVING CALCIUM

Most people get around 200 mg of calcium a day from miscellaneous foods like bread. To reach 1,000 to 1,200 mg a day, you need about three low-fat dairy products or healthy fortified foods. It's not worth buying junky fortified foods or drinks (like Sunny Delight or Hawaiian Punch) just for their calcium.

Food                                               Calcium (mg)

Dreyer's/Edy's Frozen Yogurt (1 cup)                        900

Calcium Fortified Lactaid Milk,
   non-fat (1 cup)                                          500

Yogurt, non-fat plain (1 cup)                           350-400

Milk, fat-free or 1%, protein fortified (1 cup)             350

Tropicana Premium Plus Orange juice with
   Calcium & Extra Vitamin C (1 cup)                        350

Yogurt, low-fat fruit flavored (1 cup)                  250-350

Ricotta cheese, fat-free (1/4 cup)                      100-320

Milk, fat-free or 1% (1 cup)                                300

Minute Maid Calcium Rich Orange juice (1 cup)               300

Ice cream or frozen yogurt, fat-free
   or low-fat (1 cup)                                   150-300

Swiss cheese (1 oz.)(*)                                     270

Total cereal (3/4 cup)                                  200-250

Tofu (3 oz.)(1)                                          40-250

Sardines, canned, drained (2 oz.)                           220

Cheddar cheese (1 oz.)(*)                                   205

Light n' Lively Twice the Calcium Cottage
   Cheese, fat-free or low-fat (1/2 cup)                    200

Collards, frozen (1/2 cup cooked)                           180

Salmon, canned (eaten with the bones) (1/4 cup)             100

Kale, frozen (1/2 cup cooked)                                90

Soybeans (1/2 cup cooked)                                    90

Bok Choy (1/2 cup cooked)                                    80

Cottage cheese, low-fat (1/2 cup)                            70

Parmesan cheese, grated (1 Tbs.)                             70

Orange (1)                                                   50

Bread, white or whole wheat (2 slices)                       45

Broccoli (1/2 cup cooked)                                    35

(1) Made using calcium chloride or calcium sulfate as a coagulant.

(*) High in saturated fat. Use sparingly or buy low-fat versions.

Sources: USDA Nutrient Database for Standard Reference (www.nal.usda.gov/fnic/foodcomp) and manufacturers.

RELATED ARTICLE: UPPER LIMITS

How much is too much? For the first time, the National Academy of Sciences last year issued "Tolerable Upper Intake Levels" (ULs) for calcium and a few other nutrients. They're the maximum daily levels that are "unlikely to pose risks of adverse effects" for most people.

ULs are not targets to shoot for. So why set them? When it comes to supplements, some people think more is always better. The UL is a ceiling--for food, water, and pills--that even the most enthusiastic supplement-taker should not exceed.

Nutrient    Tolerable Upper Daily   Potential Risk of
            Intake Level (UL)       Exceeding UL
Calcium     2,500 mg                Kidney stones, high
                                    blood calcium, impaired
                                    absorption of iron, zinc, or
                                    magnesium
Vitamin D   2,000 IU                High blood calcium, which
                                    could lead to calcification
                                    in the kidneys and arteries

Stephanie Atkinson is Professor of Nutrition in the Department of Pediatrics, Faculty of Health Sciences, at McMaster University in Hamilton, Canada. She chaired the National Academy of Sciences Panel on Calcium and Related Nutrients. Atkinson spoke to Nutrition Action's Bonnie Liebman by telephone.