Preventing osteoporosis: building strong bones over a lifetime

WE OFTEN TAKE OUR BONES FOR GRANTED--they're just a part of us--keeping us standing, walking, running, sitting a lot, maybe skiing or biking. We don't think about them much until something goes wrong--one breaks or bends or somehow interferes with what we want to do. As we age, we're less able to be complacent about our bones. Maybe we're more worried about slipping on a throw rug and breaking a hip, or maybe we've been diagnosed with osteoporosis or have noticed a decrease in height.

While following a vegan diet can promote bone health, it does not guarantee healthy bones. We've received notes like this one from a VRG member:

   "I'm a 58-year-old woman, vegan, post-menopause,
   and I've found out that I have osteoporosis,
   I don't understand why this is happening to me.
   I take long walks every day and eat lots of grains
   and tofu. I thought vegans didn't get osteoporosis
   because of their healthy diets ..."

This article was written to explain what osteoporosis is, what causes it, and what vegans can do at every age to reduce their risk of developing osteoporosis.

Osteoporosis is a disease that affects more than 25 million Americans. In 2001, the estimated national direct expenditure for osteoporosis and fractures related to this condition was $17 billion, and this cost is rising. Osteoporosis simply means porous bones. It is a condition in which the bones become less dense and fragile, and they can break easily. It affects women more than men, although men are also affected as they get older. If osteoporosis leads to a bone fracture, it can seriously affect function and even lead to death.

To understand osteoporosis, we'll need to look more closely at bones. Although bones seem very simple, they are actually fairly complicated. The scaffolding for bone is made from a protein called collagen. As bones form, calcium and phosphorus combine to make hydroxyapatite, a mineral-rich substance that crystallizes on the collagen scaffold, making a strong, rigid material. Bone minerals do not remain in the bone forever. Even after bones are formed, they are constantly changing. When another part of the body needs calcium, it is taken from the bone to meet the need. When more calcium is available, it is used to rebuild the bone.

Early in life, more bone is being built than is being broken down. After about age 30, though, more bone is being broken down than is being built, resulting in a net loss of bone. Although bone loss is inevitable with aging, if you have larger, stronger bones at the start, the normal loss of bone mass will not be as severe. Also, anything that can be done to slow the rate of loss helps to spare bones.

Women are at much greater risk for osteoporosis than men because women start out with less bone and lose bone mass more quickly, particularly in the years immediately after menopause. Women between the ages of 20 and 29 have about 76 percent the bone matter of men; by their 70s, this decreases to about 60 percent. (1) Thus, when women age and start losing bone mass, they develop very fragile bones. Genetics also appears to play a role in that osteoporosis runs in families.

Factors like gender and genes can't be changed. Others are within our control, though, and can have a marked effect on risk of osteoporosis. These include dietary factors, such as calcium, vitamin D, protein, sodium, caffeine, phosphorus, fluoride, vitamin A, and vitamin K, as well as weight-bearing activity.

Calcium, the main mineral in bones, plays an important role in bone health. Children whose diets are low in calcium may develop osteoporosis as adults and have a greater risk of breaking bones. (2-4) Some studies, (5-7) although not all, (8) have shown that older adults with a high calcium intake have stronger bones and a lower fracture risk. There is a limited number of studies of vegans, most of which find low bone density as well as low calcium intakes. (9-10) One study11 where vegans had calcium intakes close to recommended levels found that calcium was well-absorbed from a vegan diet. Sources of well-absorbed calcium include calcium-fortified soymilk and juice, calcium-set tofu, soybeans and soynuts, bok choy, broccoli, collards, Chinese cabbage, kale, mustard greens, and okra. (12) Grains, beans (other than soybeans), fruits, and vegetables other than those listed can contribute to calcium intake but cannot replace the key foods mentioned above.

Nevertheless, it's not enough to have a high-calcium diet. Adequate vitamin D is needed for calcium to be absorbed. Vitamin D is necessary throughout life to help build strong bones in childhood and adolescence and to maintain bones throughout adulthood. (8,13,14) Our skin produces Vitamin D with sun exposure, but many factors, including season, time of day, age, sunscreen use, and pollution, can interfere with this production. Therefore, dietary sources of vitamin D are important for most people. Since there are only very small amounts of naturally-occurring vitamin D in plant foods, vegans--both children and adults--should rely on foods fortified with vitamin D, including fortified non-dairy milks, juices, and breakfast cereals. Vitamin D supplements are another option.

Some popular publications suggest that vegans don't have to be concerned about bone health because the lower animal protein content of vegan diets will minimize calcium losses. In reality, vegans do need adequate calcium and vitamin D, and they should also be sure that they are getting adequate, but not excessive, protein. Vegan diets generally contain adequate amounts of protein unless they are very low in calories or do not contain a variety of whole plant foods.

Protein's effect on bones remains uncertain. Some studies show that diets that are high in protein, especially animal protein, do cause increased losses of calcium in the urine (seen at 0.45 grams of protein per pound of body weight and at 0.95 grams of protein per pound) (15) and may even increase fracture risk. (16,17) The effects of protein may be especially important in those with low calcium intakes. (18) Other studies suggest that a higher protein intake (as much as 0.95 grams per pound of body weight) is needed to promote calcium absorption, (19) reduce the risk of fracture, (20) and increase bone density. (21,22)

Additional research is needed, but at this time it seems that both an adequate intake of calcium and protein (near the RDA of 0.8 grams of protein per kilogram or 0.36 grams of protein per pound) can optimize bone health.

In addition, phosphorus, fluoride, vitamin A, and vitamin K are important for bone health. Phosphorus, like calcium, is a major part of bone. Phosphorus is found in many foods and is abundant in vegan diets. Fluoride promotes the accumulation of calcium and phosphate in bone. It comes primarily from fluoridated water. Vitamin A is needed for bone growth, although excessive amounts of retinol (the form of vitamin A found in many animal foods) can increase fracture risk. (23) Beta-carotene, the vitamin A precursor found in plant foods, does not appear to increase the risk of fracture. Vitamin K, a vitamin that comes from green vegetables and other plant foods, is needed to make a protein that strengthens bones.

Many substances that support bone health have been mentioned. Caffeine and sodium have the opposite effect--excesses of these can be harmful to bones. Large amounts of caffeine increase calcium losses in urine. This is especially problematic for those with low calcium intakes. (24,25) Excess sodium can also increase urinary calcium and compromise bone health. (26,27)

Any exercise that makes bones support weight-walking, running, dancing, weight-training, or roller-blading--can stimulate an increase in bone size and strength. For elementary school children, even 30 minutes of this type of exercise a couple of times a week can contribute to an increase in bone strength, which should lead to a reduced risk of osteoporosis later in life. (28) It won't hurt teens (29,30) or adults, (31) either. Besides helping strengthen bones, exercise can also improve balance and flexibility, both important factors in preventing and recuperating from falls.

In conclusion, vegans of all ages can promote bone health by:

* Consuming enough calcium and protein

* Getting adequate vitamin D from diet, sunlight exposure, and/or supplements

* Being sure to eat fruits and vegetables that supply beta-carotene and vitamin K

* Limiting use of sodium and caffeine

* Getting regular exercise, especially weight-bearing exercise.

Plant Sources of Calcium
Below is a list of plant sources that provide calcium and the amount
that a serving of each food yields:

                                    Calcium
Food/Serving                      Content (mg)

LEGUMES, 1 cup, cooked
Black beans                               46
Chickpeas                                 77
Great Northern beans                      60
Kidney beans                              50
Lentils                                   38
Lima beans                                54
Navy beans                                64
Pinto beans                               82
Vegetarian baked beans                    64

SOYFOODS

Soybeans, 1 cup, cooked                  175
Soybeans, green, 1 cup, cooked           261
Tofu, 1/2 cup                        120-430 *
Tempeh, 1/2 cup                           92
Texturized Vegetable Protein              80
  (TVP) **, 1/2 cup, rehydrated
Soymilk, 1 cup                        40-100 *
Fortified soymilk, 1 cup             200-300 *
Soy yogurt, 1/2 cup                      350
Soynuts, 1/4 cup                          59

NUTS AND SEEDS, 2 Tablespoons

Almonds                                   46
Almond butter                             86
Brazil nuts                               31
Sesame seeds                             176
Tahini                                   128

VEGETABLES, 1/2 cup, cooked ***

Bok choy                                  79
Broccoli                                  36
Collard greens                           178
Kale                                      90
Mustard greens                            76
Okra                                      88
Butternut squash                          42
Sweet potato                              35
Turnip greens                             78

FRUITS

Dried figs, 5                            137
Orange, 1 large                           74
Raisins, 2/3 cup                          53
Calcium-fortified orange juice,          300
  1 cup

BREADS, CEREALS, GRAINS

Cereal, ready-to-eat, fortified        55-315 *
Cornbread, 2-ounce piece                  141
Corn tortilla, 6-inch diameter             42
English muffin, enriched, 1                99

OTHER FOODS

Blackstrap molasses, 1 Tablespoon         172
Fortified rice milk, 1 cup            250-300 *

Notes:

* Indicates a range of calcium found in different tofu products,
fortified soymilks, fortified rice milks, and fortified cereals.

** TVP is a trademark of Archer Daniels Midland Company and is a
textured soy protein.

*** Oxalic acid, found in spinach, rhubarb, chard, and beet greens,
binds with the calcium in those foods and reduces its absorption. Thus,
these foods (which are not in the chart) cannot be considered good
sources of calcium.

Source: Data from USDA National Nutrient Database for Standard
Reference, Release 15, 2002 and manufacturers' information.

References:

(1) Widdowson EM. 1992. Physiological processes of aging: are there special nutritional requirements for elderly people? Do McCay's findings apply to humans? Am J Clin Nutr 55:1246S-1249S.

(2) Sandier RB, Slemenda CW, LaPorte RE, et al. 1985. Post-menopausal bone density and milk consumption in childhood and adolescence. Am J Clin Nutr 42:270-74.

(3) Halioua L, Anderson JJ. 1989. Lifetime calcium intake and physical activity habits: independent and combined effects on the radial bone of healthy premenopausal Caucasian women. Am J Clin Nutr 49:534-41.

(4) Kalkwarf HJ, Khoury JC, Lanphear BP. 2003. Milk intake during childhood and adolescence, adult bone density, and osteoporotic fractures in US women. Am J Clin Nutr 77:257-65.

(5) Chevalley T, Rizzoli R, Nydegger V, et al. 1994. Effects of calcium supplements on femoral bone mineral density and vertebral fracture rate in vitamin-D-replete elderly patients. Osteoporos Int 4:245-52.

(6) Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. 1997. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. NEnglJMed337: 670-76.

(7) Pecker R, Hinders S, Davies KM, et al. 1996. Correcting calcium nutritional deficiency prevents spine fractures in elderly women. J Bone Miner Res 11:1961-66.

(8) Feskanich D, Willett WC, Colditz GA. 2003. Calcium, vitamin D, milk consumption, and hip fractures: a prospective study among postmenopausal women. Am J Clin Nutr 77: 504-11

(9) Marsh AG, Sanchez TV, Michelsen O. 1988. Vegetarian lifestyle and bone mineral density. Am J Clin Nutr 48 (suppl):837-41.

(10) Chiu JF, Lan SJ, Yang CY, et al. 1997. Long-term vegetarian diet and bone mineral density in post-menopausal Taiwanese women. Calcif Tissue Int 60:245-49.

(11) Kohlenberg-Mueller K, Raschka L. 2003. Calcium balance in young adults on a vegan and lactovegetarian diet. J Bone Miner Metab 21:28-33.

(12) Weaver CM, Plawecki KL. 1994. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr 59 (suppl): 1238S-1241S.

(13) Dagnelie PC, Vergote FJRVA, van Staveren WA, van den Berg H, Dingjan PG, Haurvast JGAJ. 1990. High prevalence of rickets in infants on macrobiotic diets. Am J Clin Nutr 51:202-208.

(14) Dawson-Hughes B, Dallal GE, Krall EA, Harris S, Sokoll LJ, Falconer G. 1991. Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women. Ann Intern Med 115:505-12.

(15) Kerstetter JE, O'Brien KO, Insogna KL. 2003. Low protein intake: the impact on calcium and bone homeostasis in humans. J Nutr 133:855S-861S.

(16) Frassetto LA, Todd KM, Morris RC, Jr., et al. 2000. Worldwide incidence of hip fracture in elderly women: relation to consumption of animal and vegetable foods. J Gerontol A Biol Sci Med Sci 55:M585-92.

(17) Sellmeyer DE, Stone KL, Sebastian A, et al. 2001. A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women. Am J Clin Nutr 73:118-22.

(18) Meyer HE, Pedersen JI, Loken EB, et al. 1997. Dietary factors and the incidence of hip fracture in middle-aged Norwegians. A prospective study. Am J Epidemiol 145:117-23.

(19) Kerstetter JE, O'Brien KO, Caseria DM, et al. Nov 16 2004. The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women. J Clin Endocrinol Metab [Epub ahead of print].

(20) Munger RG, Cerhan JR, Chiu BC. 1999. Prospective study of dietary protein intake and risk of hip fracture in postmenopausal women. Am J Clin Nutr 69:147-52.

(21) Kerstetter JE, Looker AC, Insogna KL. 2000. Low dietary protein and low bone density. Calcif Tissue Int 66:313.

(22) Promislow JH, Goodman-Gruen D, Slymen DJ, et al. 2002. Protein consumption and bone mineral density in the elderly: the Rancho Bernardo Study. Am J Epidemiol 155:636-44.

(23) Feskanich D, Singh V, Willett WC, Colditz GA. 2002. Vitamin A intake and hip fractures among postmenopausal women. JAMA 287:47-54.

(24) Rapuri PB, Gallagher JC, Kinyamu HK, et al. 2001. Caffeine intake increases the rate of bone loss in elderly women and interacts with vitamin D receptor genotypes. Am J Clin Nutr 74:694-700.

(25) Massey LK. 2001. Is caffeine a risk factor for bone loss in the elderly? Am J Clin Nutr 74:569-70.

(26) Matkovic V, Ilich JZ, Andon MB, et al. 1995. Urinary calcium, sodium, and bone mass of young females. Am J Clin Nutr 62: 417-25.

(27) Devine A, Criddle RA, Dick IM, et al. 1995. A longitudinal study of the effect of sodium and calcium intakes on regional bone density in postmenopausal women. Am J Clin Nutr 62:740-45

(28) Bachrach LK. 2000. Making an impact on pediatric bone health. J Pediatr 136:137-39.

(29) Lloyd T, Chinchilli VM, Johnson-Rollings N, et al. 2000. Adult female hip bone density reflects teenage sports-exercise patterns but not teenage calcium intake. Pediatrics 106:40-44.

(30) Bailey DA, McKay HA, Mirwald RL, et al. 1999. A six-year longitudinal study of the relationship of physical activity to bone mineral accrual in growing children: the University of Saskatchewan bone mineral accrual study. J Bone Miner Res 14:1672-79.

(31) Asikainen TM, Kukkonen-Harjula K, Miilunpalo S. 2004. Exercise for health for early postmenopausal women: a systematic review of randomized controlled trials. Sports Med 34:753-58.

Sample Menu Providing Adequate Protein, Calcium, and Vitamin D for a Typical 51- to 70-Year-Old Woman Weighing 140 pounds

Breakfast:

* 1 cup ready-to-eat cereal enriched with vitamin D (like Wheat Chex)

* 1 cup calcium- and vitamin D-fortified soymilk

* 1 slice whole wheat toast

Lunch:

* Almond butter and jelly sandwich

* Carrot sticks

* Grapes

* 1 cup calcium- and vitamin D-fortified soymilk

Dinner:

* 1/2 cup kidney beans with 1 cup cooked pasta and 1/2 cup marinara sauce

* 1 whole wheat tortilla

* 1 medium orange

* 1 cup cooked collard greens (frozen or fresh)

Snack:

* 1/4 cup soynuts

* 1 1/2 cups calcium, and vitamin D-fortified orange juice

Reed Mangels, PhD, RD, is one of VRG's Nutrition Advisors. She is the co-author of Simply Vegan and the most recent American Dietitic Association position paper on vegetarian diets.

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