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Preventive Medicine and Nutrition

Preventing and Reversing Osteoporosis

Osteoporosis can lead to serious and sometimes disabling fractures, particularly in the vertebrae and hip. The condition is more common among women than men, and more prevalent among Caucasians than other racial groups. According to the National Health and Nutrition Examination Survey III, conducted between 1988 and 1991, the age-adjusted prevalence of osteoporosis in women aged 50 years and older was 21 percent in U.S. whites, compared to 16 percent for Mexican Americans and 10 percent for African Americans.¹ Similarly, a 1988 Texas study showed that hip fracture rates (a sign of osteoporosis) were much lower among African American (55 per 100,000) and Mexican American women (67 per 100,000) than white women (139 per 100,000).²

While patients tend to assume that boosting their calcium intake will ensure strong bones, research clearly shows that calcium intake is only part of the issue and that simply increasing calcium intake is an inadequate strategy. No less important is reducing calcium losses. The loss of bone mineral probably results from a combination of genetics and dietary and lifestyle factors, particularly the intake of animal protein, salt, and possibly caffeine, along with tobacco use, physical inactivity, and lack of sun exposure.

Animal protein tends to leach calcium from the bones, leading to its excretion in the urine. Animal proteins are high in sulfur-containing amino acids, especially cystine and methionine. Sulfur is converted to sulfate, which tends to acidify the blood. During the process of neutralizing this acid, bone dissolves into the bloodstream and filters through the kidneys into the urine. Meats and eggs contain two to five times more of these sulfur-containing amino acids than are found in plant foods.³

International comparisons show a strong positive relationship between animal protein intake and fracture rates. Such comparisons generally do not take other lifestyle factors, such as exercise, into account. Nonetheless, their findings are supported by clinical studies showing that high protein intakes aggravate calcium losses. A 1994 report in the American Journal of Clinical Nutrition showed that when animal proteins were eliminated from the diet, calcium losses were cut in half.⁴ Patients can easily get adequate protein from grains, beans, vegetables, and fruits.

Sodium also encourages calcium to pass through the kidneys. While patients tend to associate sodium with high blood pressure, its effect on calcium is equally important. People who reduce their sodium intake to 1-2 grams per day cut their calcium requirement by an average of 160 milligrams per day. It helps to encourage your patients to avoid salty snacks and canned foods with added sodium, and to minimize salt use in the kitchen and at the table.⁵

Caffeine�s diuretic effect causes the loss of both water and calcium, and appears to be significant at consumption levels equivalent to two or more cups of coffee per day.⁶

Smoking is also a contributor to calcium loss. A study of identical twins showed that long-term smokers had a 44 percent higher risk of fracture compared to their non-smoking twins.⁷

Active people keep calcium in their bones, while sedentary people tend to lose calcium. Physical activity may be part of the reason why people in the nonindustrialized world have fewer fractures. Simple weight-bearing exercises can be recommended for patients at virtually any age.

Vitamin D is also important, as it controls how efficiently the body absorbs and retains calcium. In a 1997 study of 389 subjects who were given either a combination of 700 IU of cholecalciferol and 500 milligrams of calcium citrate malate or a placebo each day, 11 people in the treated group had fractures over a three-year period, compared to 26 in the placebo group.⁸

A few minutes of sunlight on the skin each day normally produces all the vitamin D the body needs. However, people who get little or no sun exposure, who live in areas with less direct sunlight, who have darker skin, or who are older, may need a vitamin D supplement. The Recommended Dietary Allowance for healthy adults is 200 IU (5 micrograms) per day.

The Role of Calcium

Getting enough calcium in the diet has been emphasized in the popular press. However, calcium intake alone does not protect against osteoporosis and fractures, nor do low calcium intakes predict fracture risk. A 1992 review of fracture rates in many different countries showed that populations with the lowest calcium intakes had far fewer fractures than those with much higher intakes. For example, South African blacks had a very low average daily calcium intake�only 196 milligrams�yet their a fracture incidence was only 6.8 per 100,000 person-years, far below that of either black or white Americans, whose incidence rates were 60.4 and 118.3 per 100,000 person-years, respectively.⁹

A possible explanation for this apparent contradiction is that countries with high calcium intakes also tend to have high protein intakes. Since dairy cattle are slaughtered for meat when their milk consumption is no longer cost-efficient, dairy-producing countries also have a constant supply of animal protein. The meat consumption that is common in these countries probably contributes to their high rates of osteoporosis.

The Harvard Nurses� Health Study of 77,761 women, aged 34 to 59 followed for 12 years, found that those who drank three or more glasses of milk per day had no reduction in the risk of hip or arm fractures compared to those who drank little or no milk, even after adjustment for weight, menopausal status, smoking, and alcohol use. In fact, the fracture rates were slightly, but significantly, higher for those who consumed this much milk, compared to those who drank little or no milk.¹⁰

Healthful Calcium Sources

While an exclusive focus on calcium intake is inappropriate, the body does need calcium. The optimal calcium intake is not known. The World Health Organization recommends 400-500 milligrams of calcium per day for adults. American standards are higher, at 800 milligrams per day or even more, partly because the meat, salt, tobacco, and physical inactivity of American life leads to rapid calcium loss.

The most healthful calcium sources are green leafy vegetables and legumes, which your patients can remember as �greens and beans.� They have several advantages that dairy products lack. They contain antioxidants, complex carbohydrate, fiber, and iron, and have little fat and no cholesterol.

The calcium absorption from vegetables is as good or better than that of milk. Calcium absorption from milk is approximately 32 percent. Figures for broccoli, Brussels sprouts, mustard greens, turnip greens, and kale range between 40-64 percent.^11,12 A noteworthy exception is spinach, which contains a large amount of calcium, but in a form that is poorly absorbed. Beans (e.g., pinto beans, black-eyed peas, and navy beans) and bean products, such as tofu, are rich in calcium.

For patients looking for a very concentrated calcium source, calcium-fortified orange juice contains 270 milligrams of calcium per cup, usually in the form of calcium citrate, which has a much higher absorption fraction than cow�s milk. Calcium-fortified soy and rice milks are also widely available.

The Role of Hormones

As menopause approaches, bone loss accelerates. Doctors have attributed this loss of bone calcium to the drop in estrogens and/or progesterone. The use of prescription hormone �replacement,� using a combination of estrogens and progesterone derivatives, slows, but does not usually arrest bone loss, and their benefits diminish with time.

The most commonly prescribed estrogen, Premarin, is made from pregnant mares� urine, from whence comes its name. Other brands are synthetic or plant-derived.

Estrogens have numerous side effects, the most worrisome of which is an increase in breast cancer risk. The Harvard Nurses� Health Study found that women taking estrogens have 30-80 percent more breast cancer, compared to other women.¹³ Adding progesterone derivatives does not offset this increased risk.

A non-prescription hormone preparation, called natural progesterone, may be a safer and more effective alternative. It is an exact copy of human progesterone that is derived from wild yams or soybeans and is administered as a transdermal cream or oral preparation. The cream is preferable as it bypasses liver detoxification. In a three-year study of post-menopausal women treated with natural progesterone, bone density increased by about 15 percent, which is more than enough to have a major effect on fracture risk.¹⁴ It apparently acts by stimulating osteoblasts to lay down healthy new bone.

Osteoporosis in Men

Osteoporosis is less common in men than in women, and is often due to other health conditions, including the following:¹⁵

• Use of steroid medications, such as prednisone. Steroids are necessary in some conditions, but it is important to use the smallest effective dose and to consider other treatments whenever possible.
• Use of alcohol. Alcohol can weaken bones, apparently by reducing the body�s ability to replace normal bone losses. The effect is probably only significant at levels of more than two drinks per day of spirits, beer, or wine.
• Low level of testosterone. A lower than normal amount of testosterone can encourage osteoporosis. About 40 percent of men over 70 years of age have decreased levels of testosterone.¹⁵

In many of the remaining cases, the causes are excessive calcium losses and inadequate vitamin D. The first part of the solution is to avoid animal protein, excess salt and caffeine, and tobacco, and to stay physically active. Second, vitamin D supplements are helpful, as noted above.

References
1. Looker AC, Johnston CC, Wahner HW, et al. Prevalence of low femoreal bone density in older U.S. women from NHANES III. J Bone and Mineral Research 1995;10:796-802.
2. Bauer RL. Ethnic differences in hip fracture: a reduced incidence in Mexican Americans. Am J Epid 1988;127:145-9.
3. Breslau NA, Brinkley L, Hill KD, Pak CYC. Relationship of animal protein-rich diet to kidney stone formation and calcium metabolism. J Clin Endocrinol 1988;66:140-6.
4. Remer T, Manz F. Estimation of the renal net acid excretion by adults consuming diets containing variable amounts of protein. Am J Clin Nutr 1994;59:1356-61.
5. Nordin BEC, Need AG, Morris HA, Horowitz M. The nature and significance of the relationship between urinary sodium and urinary calcium in women. J Nutr 1993;123:1615-22.
6. Massey LK, Whiting SJ. Caffeine, urinary calcium, calcium metabolism and bone. J Nutr 1993;123:1611-4.
7. Hopper JL, Seeman E. The bone density of female twins discordant for tobacco use. N Engl J Med 1994;330:387-92.
8. Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med 1997;337:670-6.
9. Abelow BJ, Holford TR, Insogna KL. Cross-cultural association between dietary animal protein and hip fracture: a hypothesis. Calif Tissue Int 1992;50:14-8.
10. Feskanich D, Willett WC, Stampfer MJ, Colditz GA. Milk, dietary calcium, and bone fractures in women: a 12-year prospective study. Am J Publ Health 1997;87:992-7.
11. Heaney RP, Weaver CM. Calcium absorption from kale. Am J Clin Nutr 1990;51:656-7.
12. Weaver CM, Plawecki KL. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr 1994;59(suppl):1238S-41S.
13. Colditz GA, Stampfer MJ, Willett WC, et al. Type of postmenopausal hormone use and risk of breast cancer: 12-year follow-up from the Nurses� Health Study. Cancer Causes and Control 1992;3:433-9.
14. Lee JR. Osteoporosis reversal: the role of progesterone. Int Clin Nutr Rev 1990;10:384-91.
15. Peris P, Guanabens N, Monegal A, et al. Aetiology and presenting symptoms in male osteoporosis. Br J Rheumatol 1995;34:936-41.