Essential facts about bone health and osteoporosis are presented. Most studies show that avoiding calcium loss is more important than large intake of dairy products in the prevention of the disease. Exercises that do not involve bearing weights such as scuba diving are not helpful in bone building.

Why Divers Need To Know

Divers at any age need to know about bone health. Your bone density in later years depends on what you are doing right now. Until your mid-30s your bones are in an active growth phase. You can influence your final peak mass in several ways. After that there are several strategies to reduce and delay bone loss with aging. Like heart disease, bone loss is a complicated yet gradual process. The time to actively direct its course is now, before it gets serious.

What Is Osteoporosis?

Osteo is a Greek word element meaning bone. Porosis means porous. Osteoporosis is a serious degenerative bone disorder that occurs when bones lose mineral density, making them porous and fragile. Bone loss is completely painless. You probably won’t know it is happening until you break a bone. It is too late at that point to reverse the process. Osteoporosis induced hip and spine fractures are a major cause of illness and death among older women. Men are also susceptible.

The cause or causes of osteoporosis are not yet completely understood. It is important to know that calcium alone is not the big player it is made out to be. There are at least four major determinants of bone mass and consequently fracture risk: genetics, nutrition, exercise and hormonal factors. This month will cover nutritional links to bone health and a few surprises about calcium, dairy products and protein that divers of all ages need to know.

A Detective Story

Join me on an international detective story. The beginning is deceptively simple. Your bones need calcium; dairy products have calcium. Then questions creep in. Why do some groups of Japanese, whose calcium intake is historically low, develop osteoporosis while others don’t? Why do American vegetarians who shun dairy products seem to have a lower incidence of osteoporosis than the general population? Why doesn’t the very high calcium diet of Eskimos prevent their suffering the highest rate of osteoporosis in the world? Why do astronauts lose bone in space no matter what they eat?

The detective story opens with four separate studies. Researchers at the Mayo Clinic found no correlation between calcium intake and age related bone loss after bones finish forming in early adulthood. Recently at Tufts, researchers concluded calcium had no effect on preventing bone loss in the first five or so years after menopause.

Critical Factors In Bone Health

The search for these critical factors begins with the realization that just because you eat calcium doesn’t mean your bones will use it. Without exercise your bones don’t have the mechanical stimulus they need to add that calcium. Some food choices cause you to lose calcium. Others interfere with its absorption.

Where Diving Fits In

The physical stress of muscle pulling on bone during exercise stimulates bones to thicken and strengthen. By contrast, lack of exercise, prolonged immobility, sedentary lifestyle and the weightlessness of space flight lead to bone loss regardless of how much calcium ingested.

The most effective bone building exercise is lifting weights. Also important is resisting your own body weight during weight bearing exercise such as walking, dancing, running, skating and skiing. Scuba diving is not weight bearing exercise. Muscles still pull on bone to move you through the water but less than during weight bearing exercise. Carry your own tanks, if you are able, to get weightlifting exercise. If your back is already osteoporotic it may not be good to carry or wear your tank before you get in the water. The weight could further compress fragile vertebrae. In this case don your tank in the water. The buoyancy underwater is an advantage to offset the weight of a tank. Check with your physician about diving safely if you have osteoporosis.

Nutritional Factors In Bone Health

Several common foods increase calcium loss and are identified as risk factors for osteoporosis.

Meat: A succession of well controlled studies published since 1920 demonstrated that a high protein diet, specifically animal protein, increases loss of calcium through the urine. Plant protein does not seem to increase calcium loss to the same extent. One study of 1,600 women on a lacto-ovo vegetarian diet for at least 20 years found that by age 80 they had lost only 18 percent bone mineral compared to closely paired omnivore women who lost 35 percent. A high meat diet has been identified as a risk factor for osteoporosis, even if you eat a lot of calcium.

Dairy products: In 1988 a study by the Center in Mineral Metabolism and Clinical Research in Texas concluded that urinary calcium excretion owing to the animal protein of milk raised the risk of osteoporosis. Less problematic, but still of interest, is that dairy products contain lactose, which may interfere with copper metabolism. Mild deficiency of copper, common in Western diets, may relate to the development of osteoporosis.

Besides possibly being counterproductive in osteoporosis prevention, other problems occur with dairy products. The saturated fat may contribute to heart disease, breast and other cancers. Even in low and non-fat products the dairy sugar galactose, which breaks down from lactose, may pose problems. In people unable to process galactose, a 1989 study at Harvard linked galactose to increased risk of ovarian cancer in susceptible women. Other studies link galactose build up to cataracts. Dairy products are also among the most common cause of food allergies.

Other calcium robbers: You need vitamin D for calcium absorption in your small intestine. Your body makes less as you age. Other than animal protein, things you eat that increase urinary calcium loss are caffeine, salt and possibly sugar. The worst are alcohol and smoking, which may be directly toxic to the cells called osteoblasts that build bone.

Calcium Requirements

A now famous calcium study is often misinterpreted. The study, done in Yugoslavia, found that high calcium consumption related to reduced osteoporotic fracture rate. What is often missed is that the researchers found that high calcium intake increased peak bone mass in youth, which translated to lower fracture rates thereafter. They did not find that calcium in later life affected bone density. Someone with high bone mass at age 30 may lose bone through normal aging yet have sufficient bone remaining at 75. Above a minimum amount, calcium intake after bones form in adulthood was not the critical factor.

Calcium requirements vary with your food and exercise habits. Low calcium intake may be sufficient if you exercise, get sunshine, don’t drink or smoke and avoid high protein meals. High calcium intake may become insufficient if you are inactive and eat foods that rob your calcium.

Critical Clues Found

So the detective story, while not solved, reveals clues. Populations in Japan whose low protein intake comes primarily from plant sources have normal bone growth and low rates of age related osteoporosis even with calcium intakes half that recommended in the United States. For their relatives who eat a modern diet, the high protein and salt intake aggravates calcium deficiency in old age.

                                  Milligrams of
Source                             Calcium (mg)
1 cup tofu processed
with calcium sulfate                   868
1 cup dulse seaweed                    600
1 cup navy beans and
2 corn tortillas                       370
1 cup milk                             291
1 cup amaranth                         280
1 cup kale                             200
1 cup broccoli                         180
1 cup soybeans                         175
1 tablespoon blackstrap
molasses                               140
1 cup fortified orange juice           120

This phenomenon is not limited to Japanese. Studies of Bantus found almost no incidence of osteoporosis among those who ate predominantly plant diets in Africa. Their relatives in the United States eating a western diet of high animal protein suffer a fracture rate similar to those of other North Americans. Eskimos have a very high calcium diet but their high protein and sodium fish and meat meals are the likely suspects in their world’s highest rate of osteoporosis.

Sources Of Calcium

In the United States dairy products are the principal calcium source. Dairy products contain calcium that is well absorbed. Nevertheless, doubt exists concerning dairy products as a healthy major source of calcium for adults. It is not impossible to get enough calcium without dairy products. Many foods provide calcium. Contemporary hunter-gatherers have a high calcium intake, three times higher than the average middle-age American woman, without eating any dairy products.

Broccoli has more calcium per calorie than other foods. Dark green vegetables such as collards and kale are good sources of calcium with high absorption. Tofu and seaweed are good, yet frequently overlooked sources. Fruit has calcium. So do almonds and sunflower seeds. Better yet, fruits, vegetables, nuts and legumes have the element boron, which may participate in preventing osteoporosis. Milk has little boron. Meat and eggs have none.

Here’s What To Do

Reducing meat and dairy consumption is not a new idea. Seventy years of research has well established that high animal protein increases urinary calcium loss. Get your calcium from vegetable sources. You will still meet your protein needs. Reducing sugar and caffeine is another good bone strategy. Even more important, reduce smoking and alcohol.

Get your calcium throughout the day. Large amounts of calcium all at once reduce the absorption efficiency. Avoid single dose supplements and resist trying to offset two daily low calcium meals with one calcium feast.

Consider estrogen replacement at menopause. Estrogen supplementation under physician’s supervision may be the only way to maintain bone mass in the first five years after menopause.

Choose exercise with your bones in mind. A sedentary lifestyle robs you of bone density regardless of calcium supplementation. Physical activity can increase bone mass at any age. Movement alone is not enough, you need active muscular resistance. Weight bearing activities, for example walking or jogging, increase bone density, primarily of the lower body. Weightlifting can increase bone density at all sites, including the upper body. The ability of non-weight bearing exercise, such as swimming and diving, to build bone to the extent of weight bearing exercise is uncertain. Exercise and bone health will be covered more comprehensively in another article.

The Bottom Line

Calcium is not the whole story in bone health. High calcium intake is less important than reducing calcium loss. Adequate calcium intake remains a sound strategy but without other critical factors it is not a cure-all. Reduce calcium loss by limiting calcium robbing foods and increasing physical activity. Cow’s milk may be good for calves and mother’s milk for baby humans. But, for bone health, the studies say “Don’t have a cow.”

To Maintain Bone Density

Reduce meat and milk. Animal protein increases urinary calcium loss. Get your protein and calcium from a variety of vegetable sources.

Reduce smoking and alcohol. These are directly toxic to the cells called osteoblasts that build bone.

Reduce caffeine, sugar and salt. They increase urinary excretion of calcium. However, relationship to risk is still uncertain.

Consider estrogen replacement. This may be the only way to maintain bone mass in the first five years after menopause.

Remember the sunshine vitamin. Calcium absorption in the small intestine requires vitamin D.

Exercise. The most effective exercise for building bone is regular weightlifting. Weight bearing exercise such as walking, dancing, running, skating and skiing also loads bone, using your body weight.

Get calcium throughout the day. Absorption efficiency lowers with single high doses.


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