All About Calcium
Kristen Henley, a 32-year-old financial associate in Raleigh, North Carolina, leads the kind of healthy lifestyle that would make her doctor proud-she exercises six days a week and eats plenty of fruits and vegetables. There's just one problem: Her calcium intake is relegated to the amounts she reaps from occasional treats, like frozen yogurt for dessert or cheesy enchiladas from her favorite Mexican restaurant. "I'm not technically lactose intolerant-more like lactose averse," Henley says. "I drank milk when I was young, but now I just don't think about it."
Despite the best efforts of the U.S. Department of Agriculture's 2005 Dietary Guidelines (which for the first time recommended three servings of low-fat dairy foods each day) and milk-mustachioed marketers ("Got milk?"), many American adults share Henley's view. "A large number of people either don't like the taste, have gotten out of the habit of consuming dairy foods, or are lactose intolerant," says Dawn Jackson Blatner, R.D., a dietitian at Northwestern Memorial Hospital Wellness Institute in Chicago and a spokesperson for the American Dietetic Association (ADA). On average, adults consume only one and a half servings of dairy per day. According to the USDA's figures, only 10 percent of women consume the recommended three servings, compared to 27 percent of men.
That's a missed opportunity. Calcium-the most abundant mineral in the human body-offers significant benefits. The most familiar, stronger bones, is just the start.
Benefits Beyond Bones
You've probably known about calcium's relationship to strong bones since high school biology class. Bones account for more than 99 percent of the body's total calcium stores. Bone cells continually remodel, so a steady supply of calcium is needed to help form new cells. Study after study has shown the connection. Most recently, a seven-year study of more than 36,000 women found that those whose diets supplied at least 1,000 milligrams (mg) of calcium daily-the Dietary Reference Intake (DRI) for adults under age 50-reduced their risk of hip fracture by 29 percent.
The one percent of calcium not used by bones aids a wide range of functions, such as proper muscle contraction and hormone secretion. Recent research has also linked calcium to the following health benefits:
Blood pressure regulation. In a study of 450 people, researchers from the National Heart, Lung, and Blood Institute found that those with the highest calcium intake-about 1,200mg daily-had the lowest blood pressure. "A follow-up study found that eating dairy sources of calcium reduced blood pressure as much as eliminating sodium from the diet, even though the dairy-consuming subjects didn't reduce their salt intake," says Robert Heaney, M.D., a calcium researcher and professor of medicine at Creighton University in Omaha, Nebraska. Researchers don't yet fully understand the connection, but they hypothesize that maintaining adequate calcium levels helps prevent a complex chain of reactions that can cause constriction of the arteries.
Cholesterol control. Calcium can lower harmful low-density lipoprotein (LDL) cholesterol levels by as much as 10 percent. "It's a small percentage relative to other things you can do to lower your cholesterol, like consuming less saturated fats, but it may have a real impact on cardiovascular health when you add it to the blood pressure benefit," Heaney says. Other studies have found that calcium can boost levels of high-density lipoprotein (HDL) cholesterol, the "good" kind. When researchers from the University of Auckland in New Zealand supplemented the diets of 223 women with 1,000mg calcium daily for a year, their HDL levels rose by an average of seven percent. Calcium appears to block absorption of cholesterol molecules, helping to keep your bloodstream clear, Heaney says.
Reduced colorectal cancer risk. "Research shows that calcium binds with cancer-promoting toxins in the intestine, rendering them inert," Heaney says. For example, in a review of two major studies involving 1,300 adults, subjects who took calcium supplements of 1,200mg were 25 percent less likely to develop colon polyps, which can be cancer precursors.
Your Daily Dairy
If your body doesn't have access to enough calcium to meet all of these needs, it will find a source. "Because calcium influences so many vital functions, the body will actually pull it out of the bones if it's needed somewhere else," says Beth Kitchin, M.S., R.D., assistant professor of nutrition at the University of Alabama at Birmingham and a member of the Cooking Light medical advisory board. That's why meeting your daily allowance is crucial. Adults under age 50 need 1,000mg of calcium each day. After 50, the DRI increases to 1,200mg.
"As people age, their percentage of calcium absorbed decreases, so their need for it increases," Kitchin says.
You also need more calcium as you age because the balance of bone remodeling shifts, and bone cells begin to break down faster than they are rebuilt. Until a person reaches age 30, calcium's primary purpose is helping his or her bones reach their peak mass. Bone mass remains relatively stable for as much as a decade or two, but then it begins to decline. Generally, women lose about one percent of their bone mass each year starting around menopause, and men lose at about the same rate after age 55 or 60. Meeting the increased allowance of calcium can stop bone erosion.
"When people hear that bone density stops increasing in the 30s, some develop a mindset of, 'Oops, I blew it-there's no hope now,' " Blatner says. "But it's never too late to incorporate calcium into your diet for bone health-or the myriad other benefits."
Also, because estrogen helps the body process calcium, postmenopausal women should be especially careful to meet the increased calcium DRI. Conversely, women who take hormone replacement therapy or who use hormonal methods of birth control are at lower risk for calcium deficiency-related conditions, such as osteoporosis.
Where to Find Calcium
The key to tapping calcium's benefits is obtaining the mineral in multiple doses throughout the day. As important as calcium is, it can be a bit high-maintenance. The mineral isn't easily absorbed. In fact, the body can only process approximately half the day's allowance-500mg-at a time. Any unabsorbed calcium is simply passed out of the body.
What's more, other nutrients can help or hinder calcium absorption. For example, vitamin D boosts the body's use of calcium, which is the reason why its DRI also increases with age-from 200 International Units (IU) of vitamin D to 400 IU after age 50. Vitamin D signals the intestines to increase calcium absorption from food and helps maintain blood levels of the mineral. Iron, on the other hand, has the opposite effect, binding with calcium to reduce absorption.
"Food sources are the best choice for obtaining calcium," Heaney says. And the best food source, hands down, is dairy. One cup of low-fat milk, one cup of low-fat yogurt, and one-and-a-half ounces of low-fat cheddar cheese each contain about 300mg of calcium. Milk, in particular, is an excellent source of calcium because it is fortified with vitamin D; one cup supplies half of the vitamin's DRI. However, there are a number of other good food sources of calcium (see More than Milk).
Supplements are also a viable option for meeting your calcium needs, particularly for the estimated 30 to 50 million Americans who are lactose intolerant. This means that they experience difficulty digesting a sugar called lactose found in milk and, to lesser degrees, in other dairy foods. "Calcium supplements are absorbed about as well as calcium-rich foods," Kitchin says.
Calcium supplements fall into two major categories: Calcium citrate and calcium carbonate. No supplement is 100 percent calcium, so the difference between these two types is the substance the calcium is combined with to make the pill-either carbonate or citrate. Which type you pick is a matter of preference.
A typical citrate supplement only contains 300mg, so you'll have to take several pills throughout the day to meet your daily needs. Because it's cheaper to manufacture than citrate, carbonate is more widely available-in fact, most store brands of calcium supplements fall into this category. Since it's usually available in 600mg doses, you only need two pills.
Sweet, flavored calcium chews have also become a popular form of supplementation since they were introduced in 1999. The majority of brands are fortified with 600mg of calcium carbonate, and even though they're a source of calories (20 per chew), experts say they're a good, practical option. "People are much more likely to follow through with a supplement that tastes like a treat," Kitchin says. Just remember that the chews are supplements, not candy. Too much calcium is definitely not a good thing; consuming more than 2,500mg a day can cause kidney stones.
Blatner meets many people like Kristen Henley, who've left calcium-rich foods out of their personal food pyramids, and she encourages each to find easy ways to incorporate this important mineral into his or her diet. "[One of my clients] learned to blend frozen fruit into yogurt and eat it as a dessert," Blatner says. "There are so many ways to add calcium in interesting, flavorful ways. We've come a long way from the glass of milk with meals-not that there's anything wrong with that, of course."