Calcium-fortified foods: choosing them carefully

Can you get too much calcium?

So many foods are now fortified with calcium that it has gotten much easier to go over the board's safety limit. And that has some nutrition researchers concerned.

"As with anything, too much can be a problem," says Richard Wood, chief of the Mineral Bioavailability Laboratory at the Department of Agriculture's Human Nutrition Research Center on Aging at Tufts University in Boston.

And "too much" isn't all that much when it comes to calcium. "The window between optimal intake and the upper limit is relatively small," Wood points out. Indeed, the adequate intake established by the NAS is 1,000 to 1,300 milligrams a day, depending on age. Only twice that amount, and you've reached the safety ceiling. For many other nutrients, you'd have to increase the adequate intake many times before reaching risky levels.

What can happen if you take in too much calcium over time? Wood notes that there have been "on the order of 30 case reports" of calcium toxicity, which can manifest itself as fatigue, dizziness, and soft tissue calcification. The kidneys, composed of soft tissue, "might be particularly vulnerable," he remarks, and perhaps lose some of their function.

Then, too, hypercalcemia, as toxicity of the mineral is called in medical circles, can aggravate kidney stone formation, particularly for people who have had a stone in the past. Too much calcium can also reduce absorption of two other essential minerals: iron and zinc, the latter of which is necessary for wound healing and proper functioning of the immune system.

"We had a study of post-menopausal women," Wood reports. "High-calcium diets reduced zinc balance."

While such problems have been rare until now, there's a new potential threat of their becoming significantly more common. "We just don't know what the issues are going to be with chronic intake" as high as 3,500 milligrams, Wood notes.

Calcium-fortified foods can still be useful

Not that he thinks calcium-fortified foods are a bad thing. "I think they're a good idea," he says. "Average intakes are much, much lower than the recommendations."

To be sure, women 20 to 29 years old average only about 700 milligrams of calcium a day, when they should be consuming 1,000 milligrams. And those 65 and older, who should be getting 1,200 milligrams, are taking in only about half that amount. It's a similar story for men, although not quite as severe. The gap for them is often more on the order of 200 to 300 milligrams.

Others agree with Wood that calcium-fortified foods are a reasonable option for many people, who simply aren't going to get nearly enough of the mineral any other way.

"I favor the concept of fortification," says Robert Heaney, a calcium researcher at Creighton University in Omaha. And unlike Wood, he's not particularly concerned about anyone going overboard. "There are lots of very healthy people who consume lots more than [the] limit," he claims. Some populations who depend on a largely dairy diet, such as cow herders in East Africa and the Laps who herd reindeer in northern Scandinavia, "typically get 6,000 to 7,000 milligrams of calcium per day" and have "absolutely no problems," he says.

Which foods should be fortified with calcium?

But he and others do have some reservations about which foods the mineral ought to be added to.

For instance, Breyer's is now test marketing ice cream that contains 300 milligrams of calcium per half cup instead of the typical 100 milligrams, and Heaney remarks, "I've got mixed feelings on the junk food situation."

Adds Connie Weaver, a calcium researcher at Purdue University in West Lafayette, Indiana, people do take in too little calcium, but "America has this other problem of obesity. I'd hate to see people use the excuse of needing to get enough calcium to eat lots of fat and calories. Then you're solving one problem while making another one worse."

Bess Dawson-Hughes, chief of the Calcium and Bone Metabolism Laboratory at Tufts, agrees, saying that while Breyer's has added calcium to ice cream at a "responsible level, ice cream as a responsible vehicle" for delivery of that nutrient "is another question." She's not opposed to someone with low calcium intake choosing calcium-fortified ice cream if he or she is going to eat ice cream anyway. But, she says, "I wouldn't want to promote ice cream consumption in this country with all the overweight people."

Dawson-Hughes does not feel that the 1,000 milligrams of calcium now added to every cup of Total cereal is responsible. "That's an excessive level of fortification," she comments. It certainly is an unprecedented level, probably higher than in any other calcium-fortified food.

How much calcium will you actually absorb?

Weaver also has some reservations. "It may not be the way I would design a cereal," she comments. She also points out a limitation of a product like Total, which contributes so much calcium per serving. "You will absorb more calcium if you have divided doses throughout the day," she says. That's why people who take 600 milligrams' worth of calcium supplements daily are advised to swallow their two 300-milligram pills at different meals.

Just how much of the 1,000 milligrams you absorb from a cup of Total is something Heaney learned when he did bioavailability testing for Total producer General Mills. What he found was that the calcium in the cereal is absorbed just as well as the calcium in milk. For every 300 milligrams of calcium (the amount in a cup of milk), the body gets about 100 milligrams, or roughly 30%. But as the calcium in a single meal goes up, the absorption rate goes down. If you have three to four cups of milk in one sitting and get about 1,000 milligrams, the absorption rate dwindles to 15%, or about 150 milligrams. It's the same with the Total. Since one cup supplies 1,000 milligrams, you absorb only about 150 of them, Heaney says. In other words, you're not absorbing terribly much more calcium than if a bowl of the cereal contained 300 to 400 milligrams of the mineral.

Of course, says Purdue's Weaver, for people getting 200 to 400 milligrams of calcium in their daily diet, the cereal could still be useful. And a lot of people do get only that much.

Wood concurs. "If you don't drink milk, your calcium consumption is about 300 to 400 milligrams a day," he says he tells people. "That's a rule of thumb people should know."

With the exception of Heaney, though, the researchers agree that it's safest not to consume more than 2,500 milligrams of calcium daily. "Count up," Weaver says. "Make sure you're not going above 2,500."

Adds Wood, "One should just shoot for the recommended intake [of 1,000 to 1,300 milligrams]; there's no convincing evidence that higher intakes are beneficial."

He says that staying within the limit is a particular concern in households with, say, a mother trying to get more calcium and her teenage son who already gets plenty by sheer dint of the amount of food he eats. She might buy calcium-fortified orange juice, calcium-fortified milk, cereal, and so on, but if he guzzles milk or juice out of the container after football practice or has a couple of bowls of fortified cereal as an after-school snack, he could easily be getting thousands and thousands of milligrams of calcium daily.

Get your calcium from a variety of foods

Wood and other researchers also agree�and Heaney is with the group on this�that it's best to get your calcium from a variety of foods rather than one or two heavily fortified ones, and that at least some of it should come from milk and other dairy products.

"Historically," Weaver explains, "people who have been deficient in calcium have been low in magnesium, riboflavin, vitamin A and vitamin D"�all available in milk. "Dairy was a kind of one-stop shopping for this package of nutrients," she notes, "so it makes it a little more difficult" if you're going to get calcium but not necessarily these other substances from calcium-fortified foods.

Irwin Rosenberg, director of the Nutrition Research Center at Tufts, is particularly concerned that a food with a high concentration of a single nutrient will lull people into thinking they've got their diets in good shape.

"You don't get off the hook of making prudent dietary choices because you've picked one or two heavily fortified foods," he says.

James Fleet, a mineral researcher colleague of Weaver's at Purdue, points out, too, that you don't even have your bones completely protected just because you're getting a lot of calcium.

"Bone density is also strengthened by exercise," he says. "And it's weakened by too little vitamin D," which is necessary for calcium absorption�and perhaps by too much sodium and caffeine as well, according to research. Both substances work to flush the mineral from the body via the urine.

In other words, as Heaney puts it, "calcium is only one part of the puzzle. Just because you've had a bowl of Total doesn't mean you've covered all the bases."