The Nature of Nutrients

It sounds like a simple question of logic. If bones require calcium, then people who eat a lot of calcium-rich dairy products should have extra-strong bones, right? So why are hip fractures uncommon in Singapore, where adults don't drink milk, while they soar in dairy-loving Scandinavia? "Countries with higher calcium intakes have the highest fracture rates, not the lowest," says Dr. Walter Willett, chair of nutrition at the Harvard School of Public Health. It's the Calcium Conundrum.

Scientists have identified nearly 40 vitamins and minerals that the body needs for various tasks, from shoring up bones to bolstering the immune system and repairing cellular damage. But as the Calcium Conundrum suggests, they work more subtly than drugs. Instead of delivering predictable effects at particular doses, they team up in complex ways that we're just beginning to understand. Forgo your daily orange for a vitamin C pill, and you will miss out on other compounds that protect the heart, fight cancer and combat infections. "You can't just pop vitamin E over hot-fudge sundaes and expect to get any benefit," says nutritionist Alice Lichtenstein at Tufts University.

But don't mistake the subtlety of these compounds for a lack of power. Exciting new findings are pouring out of the nation's research labs, linking long-neglected nutrients to everything from brain function to cancer risk. And it's increasingly clear that, despite our abundant food supply, we're still getting too little of some crucial vitamins and minerals. Here are some of the latest insights on how eating well can help us live well--and target some of our most common dietary deficiencies.

CALCIUM as it turns out, this mineral really is critical to bone strength. But as scientists are now learning, it doesn't work by itself. Healthy bones require a mix of calcium, phosphorus and magnesium. They also need adequate protein to form their basic framework, vitamin K to maintain structural proteins and two other bone strengtheners that we're probably even shorter on than calcium: vitamin D (for calcium absorption) and exercise (to stimulate bone-building cells). Put it all together, and one potential explanation for the calcium paradox jumps out. Though doctors say genetic differences are partly responsible, vitamin D levels must be playing a role too. If you consider that we get most of our vitamin D from sunshine striking the skin, it's logical that people who live near the sun-drenched equator absorb their calcium better and suffer fewer bone fractures.

But calcium does more than build strong bones. It is crucial for transmit-ting nerve impulses and maintaining a regular heartbeat. It stimulates hormone secretions and activates enzymes. It may even help protect against colon cancer. And most people could stand to consume more. "Only half of Americans are getting the required amount," says Dr. Felicia Cosman of the National Osteoporosis Foundation. Recommended intake is 1,000 milligrams a day for adults--1,200 for women older than 50 and 1,300 for teens.

VITAMIN D when epidemiologists Cedric and Frank Garland began mapping the incidence of colon cancer in the United States back in the 1970s, they noted a curious pattern. People in the South were half as likely to die of the disease as those in the Northeast. Could the reason be the sunshine vitamin--D? Since then the research has grown, linking vitamin D with lower risks of not just colon cancer but also breast, prostate and ovarian cancers. That's not all. People with higher levels of D are less likely to suffer autoimmune diseases, including type 1 diabetes and multiple sclerosis. They may even have less heart disease and better lung function. "I'm not an alternative-medicine nut who says one nutrient is good for everything," says biochemist Reinhold Vieth at the University of Toronto. "But vitamin D might be."