Food Becomes You - Your Bones Should Outlast You

Ten million Americans, mostly women, have osteoporosis and another 18 million have low bone mass, placing them at increased risk of osteoporosis, according to the National Osteoporosis Foundation. Often the first sign of osteoporosis is a fracture, usually of the hip, wrist, or spine. Height loss and related spinal problems are also common symptoms. That's the bad news. The good news is that this crippling disorder is largely preventable.

Calcium is the first nutrient that comes to mind when talking about osteoporosis, and rightly so. Calcium is the major constituent of bone, but it is actually continually in flux, moving in between the bones and bloodstream depending on the body's needs. Calcium is critical to the most basic cellular functions: regulating the heartbeat, transmitting nerve impulses, blood clotting, and absorption of other nutrients. When people don't take in enough calcium to meet their needs, the body draws the calcium it needs for survival from the bones and teeth. Conventional wisdom states that bone density reaches its maximum level at age 25, but there's some evidence that this is a rather arbitrary limit. After menopause bone density will definitely decrease without protective action.

However, just like cholesterol and heart disease, there's no direct link between dietary calcium intake and bone density. Things are far more complicated than that. For one thing, there's a definite genetic component. Caucasian women - ironically the racial group that eats the most calcium - are the most prone to osteoporosis. While there is no specific clinical proof of this, perhaps their bodies do not absorb calcium as efficiently. Low body weight is another risk factor, especially for women with a history of eating disorders, or sports that promote abnormally low body fat and irregular menstruation (most notably gymnastics and ballet). On the other hand, weight-bearing exercise (walking, jogging, cycling, weight lifting) builds bone density, so overly sedentary people are also at risk. Certain medications, most notably prednisone and anti-seizure drugs, leach calcium out of the body. So do tobacco and alcohol.

Calcium also interacts with other nutrients in the body, most notably vitamin D, sodium, phosphorus, magnesium, potassium, and protein. Hormones made from vitamin D transfer calcium into bone, so if you don't get enough vitamin D (see last issue's article!) your body won't be able to utilize the calcium you eat. Excess sodium and phosphorus increase urinary calcium excretion. Avoiding processed foods should zap sodium out of the danger zone. Soft drinks contain tons of phosphorus as well as replacing other beverages higher in calcium. Limit them to one a day at most.

Protein also increases urinary calcium excretion. Our RDA for protein is 46-50 grams for women and 65-70 grams/day for men, but the typical American woman eats 65-70g/day and the typical American man 90-110g/day. Each of these additional grams of protein results in an additional loss of 1.75 mg of calcium per day. Now that low-carb diets have become so popular American protein intake is probably higher than ever. Increased risk of osteoporosis is yet another reason to shun this fad.

On the other hand, recent research shows that a diet high in fruits, vegetables, and whole grains contributes to the maintenance of bone mineral density. One of the main reasons may be that these foods are rich in potassium and magnesium. The exact interactions between the three minerals are unclear, but potassium and magnesium do seem to maintain bone density, especially in the elderly.

Osteoporosis prevention is one of many reasons to quit smoking, and to keep alcohol consumption at a moderate level (up to 7 drinks/week). One substance you can continue to enjoy is coffee. While caffeine technically increases calcium excretion, you'd have to be a major caffeine junkie for this to have any practical effect.

According to the USRDA, women 19-50 require 1000mg calcium/day; women over 50 1200mg/day. But of course this is just an average. To determine your optimal calcium intake, take into account your genetic heritage. Women of Caucasian descent, with petite builds, or with osteoporosis in the family, should make a special effort to eat enough calcium. Adolescent girls and pregnant and nursing women should eat extra calcium at these times of special demand. Postmenopausal women also need more calcium, as their lack of estrogen prevents their bodies from utilizing calcium as efficiently. All postmenopausal women and any women with a history of eating disorders or excessive fractures should have a bone density test. In the past, these tests were not particularly informative, but now dual-energy x-ray absorptiometry (dexa scans) provide a safe and precise measure of bone density. DEXA scans can be used over the entire body, but are generally used on the spine and hip bone, as low densities here are the most predictive of later problems.

Because calcium interacts so intricately with other nutrients, it's best to obtain as much calcium as possible from food. Obviously dairy products (milk, yogurt, cheese) are an excellent source of calcium, but other foods are as well. Most dark green vegetables, beans, and nuts are good calcium sources. Special (and surprising) stars include baked beans, refried beans, black beans, edible-boned fish like sardines and anchovies, collard greens, spinach, almonds, and figs. Tofu is an excellent calcium source, although soy milk isn't necessarily (read the label).

A 500-1000mg calcium supplement is also a good idea for many women. Choose your supplement from a reputable source and make sure it contains 200-400 IU vitamin D. Calcium citrate is more absorbable than calcium carbonate. Take your supplement with a meal, as the stomach acid produced at mealtime helps your body absorb the calcium. Some people think that splitting the dose up into 2-3 segments aids absorption, but if that sounds like too much of a nuisance it's OK to take all your calcium at once.

And don't forget to get out there and exercise! Weight bearing exercise is probably just as important as diet in preventing osteoporosis. Besides, while you're out walking, jogging, or cycling, you'll be absorbing some healthful vitamin D.