Bone Up on Osteoporosis
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From The November 2000 Issue of Nutrition Science News
by Carmia Borek, Ph.D.Lifestyle and dietary approaches can prevent this debilitating condition
Bones are amazing living structures that are constantly being remodeled throughout life. Bones continuously mend and rebuild themselves by the opposing actions of two types of cells: the osteoblasts that form bone and the osteoclasts that resorb (destroy) bone. When the activity of the bone-destroying osteoclast cells outpaces that of bone-forming osteoblasts, the bottom line is bone loss and increased osteoporosis risk.
Osteoporosis currently affects more than 26 million Americans, of whom 20 million (77 percent) are women. [1]In 1995, the medical costs of treating osteoporosis were estimated at $13.8 billion and were predicted to increase to $162 billion by the year 2020. Disease risk increases with age, as does rate of injury. Therefore, one-third of women who reach 65 will have a vertebrae fracture, and of those women who reach 80 years, 32 percent will suffer a hip fracture. [1]
Osteoporosis develops less often in men because they generally start with more bone mass, their bone loss begins later in their lives, and they incur no period of rapid hormonal change that is linked to bone loss. [2 ]However, men suffer hip fractures at high rates after the age of 70 (17 percent of 80-year-olds). In addition to hip fractures, men older than 70 frequently have debilitating spine, wrist and other bone fractures.
The Nature of the Condition
Osteoporosis silently breaks down the skeleton. Bone substance loss makes bones more fragile, resulting in spontaneous fractures, especially of the vertebrae and hip. Bone loss and osteoporosis occur in otherwise healthy people as result of many factors, possibly including heredity. One way women lose bone is menopause-related decreases in estrogen levels. Normally, estrogens bind to bone-forming osteoblasts, causing a chemical secretion that prevents osteoclasts from breaking down bone. Estrogens, therefore, help conserve bone by reducing bone loss and increasing bone density. The onset of menopause removes this protection. Men, incidentally, also lose estrogens as well as male hormones (androgens) as they age, but at a slower rate than women.
A lack of physical activity also increases osteoporosis risk, as does exposure to various pollutants and toxins, such as those in cigarette smoke. Insufficient intake of nutrients, particularly calcium and vitamin D, which play major roles in bone building, is one of the strongest promoters of bone loss—and also one of the most reversible risk factors.
Nutrients That Help Build Bones
Since they are living tissues, bone cells need the same kinds of nutrients as do other cells in the body. But bones need extra nutrients to help osteoblasts form new bone and prevent bone loss. Following are some of the nutrients, in order of importance, known to aid in these functions.Calcium is one of the principal components of bone and is absolutely essential for bone formation. During the first 20 years of life, bone minerals accumulate in the skeleton. However, bone mineral loss begins after age 30. In women, this loss can be slowed with a combination of calcium and vitamin D supplementation. [3] Although there are few studies of bone loss in men, there is evidence that dietary intake of more than 1,000 mg a day of calcium may slow this process in men as well. [4]
Fortunately, if a lifetime of high calcium intake has not been possible, women's studies show bone density still can be improved by increasing calcium and vitamin D intake before a woman enters menopause. Moreover, high levels of calcium supplementation are especially important for patients receiving currently approved bone-maintaining drugs for the prevention of osteoporosis such as estrogens, Raloxifene and Alendronate.
Dairy products are the richest food sources of calcium, followed by soy and broccoli. [5] Calcium supplements such as calcium carbonate and calcium citrate are also readily available. Which of these two forms is better-absorbed is unknown because analysis methods have varied. Regardless of how it is obtained, the recommended daily calcium intake is 1,200 mg for postmenopausal women and 1,000 mg for premenopausal women. [3] Women in menopause who are not on hormone replacement therapy (HRT) are often advised by their physicians to increase their daily dose to 1,500 mg.
Vitamin D is a derivative of cholesterol made in our skin during exposure to the sun's ultraviolet (UV) rays. Once formed, vitamin D (called cholecalciferol) is then converted to an active form (1,25-dihydroxycholecalciferol). This active vitamin D regulates several biochemical processes including calcium absorption from the intestines and reabsorption from the kidneys destroying bone by depositing calcium and bone building phosphate in bone, and by releasing calcium and phosphate from bone (bone demineralization). Levels of dietary calcium and vitamin D must be adequate to maintain the actions of these two nutrients. A deficiency in either or both will lead to bone loss. Food sources rich in vitamin D are saltwater fish, fish oil, eggs, milk and other dairy products that are fortified with vitamin D.
The required intake of vitamin D from both food and supplements is 400800 IU/day. Doses should not exceed 800 IU/day because of possible side effects including excess calcium in the blood and kidney stone formation. [6] In the elderly who are homebound and have little sun exposure, vitamin D supplementation is especially important to prevent deficiency and resulting bone loss.
Vitamin K is a fat-soluble vitamin that exists as K1 in plants and as K2 when formed by bacteria in the human intestine. Vitamin K is required for proper blood clotting and for chemical modifications of a bone protein called osteocalcin, which is important in bone remodeling. Low serum concentrations of vitamin K have been linked to increased hip fracture risk. [7] Foods rich in vitamin K include alfalfa, broccoli, cabbage, lettuce, soybeans and turnip greens.
As part of the large, prospective Nurses' Health Study that began in 1976, researchers at Brigham and Women's Hospital and Harvard Medical School in Boston carried out a collaborative study between 1984 and 1994 on the relationship between high vitamin K intake and lowered hip fracture risk in women. [7] In the study, 72,327 women aged 38 to 63 filled out food frequency questionaires during a 10-year period. By 1994, 270 of the women had fractures following slight or moderate injury. The researchers found that, during the 10-year follow-up period, women who ate less than 109 mcg vitamin K/day (20 percent of women in the study) had a 30 percent higher hip fracture rate. [7] These results suggest that dietary vitamin K intake requirements should be based on bone health as well as on blood coagulation, and that the RDA of 65 mcg/day is too low to prevent bone fractures.
The assessment of vitamin K intake in this study was based on the amount of broccoli, brussels sprouts, greens and iceberg lettuce consumed by participants. Researchers found that women who ate lettuce each day had a significantly lower risk of hip fracture (45 percent) compared to those who ate lettuce once a week.
Magnesium , with an RDA of 280–350 mg, is involved with other minerals in the bone-building process and is necessary for regulating blood-calcium levels. Sixty percent of the magnesium in the body is located in bone. Magnesium is present in many foods; rich sources include cocoa, nuts, seeds and whole grains as well as fruits and vegetables. Animal studies have shown that magnesium deficiency leads to impaired bone growth and enhanced osteoclast activity that, in turn, leads to increased bone loss and skeleton fragility. [8]
Using data from the Framingham Heart Study that began in 1948, researchers at the Human Nutrition Research Center on Aging at Tufts University in Boston examined the relationship between bone density and intake of dietary magnesium, potassium, and fruits and vegetables that are high in these minerals. The study reviewed the dietary records of men and women aged 69 to 97, between 1988 and 1993. The results showed that a greater intake of these nutrients led to increased hip and forearm bone density in both men and women. [9]
Other minerals play a role in keeping bones strong. Metabolic studies have shown that potassium, with a recommended estimated intake of 2,000 mg/day, promotes calcium retention by the kidneys and thereby prevents loss through excretion. By improving calcium balance, potassium influences bone health.
Phosphorus is another mineral that is as important for bone formation as calcium. In the form of phosphate, it makes up nearly half of bone minerals. It is found in all foods and many soft drinks. The RDA for phosphorus is 1,200 mg/day, reduced to 800 mg/day for women and men older than 51. [10] There has been concern that drinking soft drinks results in excessive amounts of phosphates, which actually promotes bone loss. High intake of these products can suppress the hormone calcitriol, which is needed for calcium absorption. Reduced calcium absorption leads to other hormonal changes that promote bone loss and increase the risk for osteoporosis.
In addition to the right amounts of phosphates, several minerals – notably zinc, manganese, boron, copper and fluoride – are needed in trace amounts as cofactors for building bone. These trace minerals are found in a balanced diet containing fruit, vegetables, grains, nuts, seafood, meats and dairy. These minerals accumulate in minute amounts in bone, keeping them healthy.
Zinc, with an RDA of 1215 mg/day, is needed for the activity of more than 200 enzymes, one of which is responsible for incorporating minerals into bone matrix. Manganese, with no RDA but an Estimated Safe and Adequate Daily Dietary Intake (ESADDI) of 2.02.5 mg for adults, is important for forming collagen in bone. Boron has no RDA but no more than 1 mg/day is required. It affects bone strength and is needed for calcium and magnesium metabolism. Copper, a cofactor for many enzymes involved in bone formation, has no RDA but an ESADDI of 1.53.0 mg. Copper deficiency in animals results in osteoporosis. Fluoride, with no RDA but an ESADDI of 1.54.0 mg, is required for hardening bones and teeth. Taken in great excess, fluoride begins to accumulate in soft tissue and leads to deformed bones. [11]
Soy foods contain calcium and potassium, two minerals, as explained above, that are important for bone health. Soy also contains isoflavones, which are capable of binding to estrogen receptors on cells but that have other nonhormone benefits as well. When isoflavones bind to estrogen receptors, they prevent estrogen from binding to these same sites and exerting its effects. Since it is believed that many cancers are estrogen-dependent, blocking the actions of estrogen can at times be important in health maintenance.
Most research demonstrates that soy foods also increase mineral density in menopausal women and reduce bone loss; however, many of the studies have been short-term and have involved only small numbers of women. [12] Furthermore, the appropriate dose of soy needed to protect against bone loss is still unknown.
In addition to isoflavones' direct effect on bone, soy protein may increase bone strength indirectly. Animal studies show that soy protein decreases calcium excretion from the kidneys, which suggests that people who eat soy foods may reap a similar benefit. [12] Animal studies also demonstrate that soy isoflavones prevent bone loss in female animals that are made estrogen-deficient by removal of their ovaries [13]—offering hope to both menopausal women and those who have had hysterectomies.
Ipriflavone is a synthetic form of naturally occurring isoflavones. Synthesized from the soy isoflavone daidzein, ipriflavone has shown promising results in a number of studies for its ability to increase bone density. In one such study conducted by researchers in Siena, Italy, 56 postmenopausal women with low vertebral bone density were randomly assigned to receive either 200 mg ipriflavone three times a day or placebo. All subjects also received 1,000 mg/day of calcium. After two years of treatment, women taking only calcium showed close to 5 percent decline in vertebral bone density. However, no change was seen in women taking ipriflavone, indicating that the isoflavone prevented rapid bone loss following menopause. [14]
In a separate study conducted at Keio University in Tokyo, 60 women with postmenopausal bone loss or osteoporosis received either 600 mg/day ipriflavone or 800 mg/day calcium lactate. Bone density of the second and fourth vertebrae was evaluated as was bone metabolism. After one year of treatment, the ipriflavone-treated group's bone density remained the same as before treatment. In contrast, subjects treated with only calcium showed a marked decrease in both rate and amount of bone mineral density, suggesting that the isoflavone suppressed bone resorption. [15]
While ipriflavone seems to increase estrogenic effects by preventing bone loss and increasing bone formation, it does not appear to increase risk of breast cancer in the way estrogen therapy can. Therefore, based on available data, ipriflavone may be an attractive adjunct or alternative to conventional HRT for postmenopausal women.
Some early studies show that ipriflavone prevents the bone loss associated with therapeutic steroid use, immobility, ovariectomy and other conditions associated with bone loss. [16 ]
The data on naturally occurring isoflavones—found in the greatest amounts in soy but also present in clover, cabbage and other legumes and plants—are limited but suggest that their inclusion in the diet could result in a reduction in bone resorption caused by estrogen deficiency. The data are more extensive on ipriflavone, and studies suggest that it is a useful and safe alternative to estrogen therapy for treating osteoporosis in postmenopausal women. Additional studies are needed to examine ipriflavone's role as a preventive agent as well as to assess the clinical effects of the naturally occurring isoflavones in maintaining bone health.
Better Bone Care
Osteoporosis develops in older adults when bones are broken down quicker than they are formed. Bones become thin and fragile and fracture easily. Estrogen loss due to menopause and aging helps trigger the condition. Poor dietary habits, smoking, high alcohol intake and lack of exercise also promote osteoporosis.
Osteoporosis can be effectively and easily prevented with dietary modifications. Although the primary goal is to achieve peak bone mass in early adulthood, with adequate calcium intake, good nutrition and exercise, it is never too late to stay a step ahead of osteoporosis.
Sidebars:
Exercise And Osteoporosis
Homeopathy Addresses Osteoporosis
Carmia Borek, Ph.D., a research professor at Tufts University School of Medicine in Boston, is author of Maximize Your Health-Span With Antioxidants: The Baby-Boomer's Guide (Keats Publishing, 1995).
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