A New Look at Bone Health -- July 2007
Why such early intervention? Bone is in a constant cycle of resorption (breaking down) and new formation. The forming of bone exceeds resorption in these early years, resulting in a net accrual of bone with about 50% completed by adolescence and reaching 90% by the age of 18. Bone formation will continue to outpace resorption until peak bone mass (maximum bone density and strength) is reached at around age 30. Thereafter, bone resorption slowly begins to exceed bone formation. Like protecting your skin from the sun early in life to avoid wrinkles and skin cancers, the benefits of protecting your bones also will not be visible for years, as the onset of ostoporotic symptoms usually does not occur until after 50.
Osteoporosis, which literally means porous bones, is a disease that reduces bone mass and increases bone fragility. According to the National Institutes of Health, osteoporosis is a major public health threat for 44 million Americans, 68% of whom are women. One out of every two women and one in four men over 50 will have an osteoporosis-related fracture in their lifetime. Although there are uncontrollable factors that put one at risk for bone loss such as gender, genetics, body size and age, there are numerous lifestyle choices that lead to better bone health. Fortunately, the factors having the most influence in reducing the risk of osteoporosis are already familiar to usâ€”a healthy diet (specifically optimal levels of calcium and vitamin D) and regular physical activity.
Vitamin D and CalciumCalcium and vitamin D are the mainstays of supplementation for prevention of osteoporosis. The connection between calcium and reducing the risk of osteoporosis was made over 50 years ago, eventually spurring one of the first FDA-approved health claims in foods in the Nutrition Labeling and Education Act of 1990. This health claim drove the huge growth of calcium-fortified foods such as orange juice and breakfast cereals, which many consider to be the first “functional foods.” In January of this year, following the review of scientific evidence supporting the combination of calcium and vitamin D for reducing the risk of osteoporosis, the FDA has proposed updating this health claim to include the addition of vitamin D, which works by optimizing the absorption and deposition of calcium. Since vitamin D is found naturally in very few foods, many functional foods manufacturers have already sprinted to market with products containing the calcium and vitamin D combination. This proposed new claim will likely increase this trend.
Other VitaminsAs the expected life span in the U.S. increases and as the Baby Boomer generation ages, the number of people diagnosed with osteoporosis is expected to increase and reach epidemic proportions. In fact, the president has declared 2002–2011 as “National Bone and Joint Decade” to raise awareness and promote research into therapies and preventative measures for bone diseases such as osteoporosis. Research is now looking beyond calcium and vitamin D and confirming epidemiological studies with clinical trials. One example is the recent clinical research on vitamin K2. The journal Osteoporosis International just reported that vitamin K2 supplementation (45mg per day) improved bone strength in postmenopausal women by improving bone mineral content. Vitamin K2 enhances the accumulation and production of osteoclain, a bone matrix protein that has an affinity for bone mineral constituents. Vitamin K2 is available both in the synthetic form (MK-4 or menatetrenone) and a naturally derived form from the fermented soy product natto (MK-7 or menaquinone). MK-7 requires a lower dosage compared to its synthetic counterpart, possibly because supplementation with MK-4 has been reported to result in more stable serum levels.
Another vitamin which may be important for both men and women in maintaining strong bones is vitamin B12. The Framingham Osteoporosis Study, conducted by the USDA Human Nutrition Research Center on Aging, measured bone mineral density and vitamin B12 levels in over 2,500 participants and found that both men and women with lower B12 levels had lower bone mineral densities. The study also reports that older adults often have B12 deficiencies, because they may have difficulty absorbing protein-bound vitamin B12 as it is found naturally in foods. However, unbound vitamin B12, as found in supplements or fortified foods, is better absorbed. This information provides good reason for the addition of B12 in functional foods and supplements geared towards bone health.
Other MineralsOther key minerals, such as magnesium and phosphorous, work synergistically with calcium and vitamin D to increase bone mineral content. Phosphorous binds with calcium to form hydroxyapatite, the main mineral component of bone, which also requires magnesium for crystallization. Phosphorous absorption is also regulated by vitamin D. However, formulators of bone health products must pay particular attention when combining these minerals, as they may interfere with each other. For instance, magnesium taken at the same time as phosphorous reduces phosphorous absorption. The Framingham Study also found a correlation between the consumption of cola, which contains phosphoric acid, and low bone density. The study suggests that phosphoric acid may be the culprit, because it changes the body’s normal calcium/phosphorous ratios. The newest mineral recognized for its potential in bone health is silicon. The Journal of Nutrition Health and Aging reported epidemiological evidence supporting positive associations between dietary silicon intake and bone mineral density.
Prebiotics and Bone HealthThere is emerging research on ingredients beyond vitamins and minerals for bone health such as prebioticsâ€”specifically oligofructose-enriched inulin. Inulin is in the category of natural oligosaccharides, which are polymers of simple sugar molecules, mostly fructose. This form of soluble fiber is found in many vegetables and roots such as chicory root, bananas, barley and Jerusalem artichokes. In the body, inulin is converted oligofructose, also known as fructo-oligosaccharides (FOS). These shorter fructose polymers are not digested in the intestines and beneficially affect the microflora in the colon by selectively stimulating the growth of various bacteria species. The effect of FOS on bone health is multifaceted. The increased bacterial production increases the production of short chain fatty acids, which are believed to decrease the pH inside the colon, thus increasing the solubility of minerals such as calcium. Fermentation products of the modified flora also mediate an enlargement of the absorption, allowing for higher transport of nutrients into the tissue. FOS has been shown to increase the levels of certain calcium-binding proteins in the large intestines, degrade phytates, the calcium-binding plant molecules found in beans, nuts and grains, and increase the release of phytoestrogens from foods believed to have bone-conserving properties.
Recent clinical trials have shown that supplementation with oligofructose-enriched inulin, a combination of short-and long-chain fructose polymers, significantly increases calcium absorption in both postmenopausal women and adolescents. In a trial published in the American Journal of Clinical Nutrition, pubertal adolescents were randomly assigned either 8g per day of mixed short- and long-chained inulin-type fructans or a placebo. The calcium absorption in the fructan group was 8.5% greater than the control group after eight weeks and 5.9% greater after one year. The fructan group also showed higher whole-body bone mineral content and whole-body bone mineral density. A second study reported that post-menopausal women had increased calcium and magnesium absorption after six weeks of supplementation with a mixture of chicory oligofructose (short-chain polymers) and long-chain inulin.
SoyIt is well-established that estrogen, in the form of hormone replacement therapy, has been linked with reduced risks and symptoms of osteoporosis in post-menopausal women. With the current trend to move away from synthetic estrogen therapy, the question naturally arose whether phytoestrogens, such as soy isoflavones, would have similar effect on bone health, particularly following menopause. While animal studies, which have been conducted predominantly with animals whose ovaries have been surgically removed, have been promising, studies with humans have been inconclusive and at times contradictory. The complex set of risk factors associated with osteoporosis, such as environment-genetic interactions, life stage and ethnicity, combined with the small sample sizes and the variations in the study conditions makes it difficult to reach definitive conclusions. A recent clinical trial introduced yet even another variableâ€”a woman’s ability to produce equol, the more biologically-active metabolite of daidzein, the principal isoflavone from soy. This clinical trial of postmenopausal women suggests that there is a more positive effect of isoflavone supplementation in women who are better equol producers. The results of the study showed significantly smaller annual reduction in bone mineral density in equol-producing women supplemented with soy isoflavones compared with non-equol producers who were also supplemented.
The debate on whether soy isoflavones have an effect on bone health continues to swing back and forth. The debate may swing towards the positive side with the recent results of a meta-analysis using nine studies and over 430 menopausal women. This analysis reported that isoflavone intervention significantly inhibits bone resorption and stimulates bone formation with as little as 90mg per day. On the other hand, the debate may balance out with the recent study of 13 post-menopausal women in which soy isoflavones did not affect bone resorption. This particular study is noteworthy because it is the first to use a new, quick and more powerful technique of monitoring changes in bone metabolism using 41Ca, a radioisotope of calcium.
Epidemiological studies suggest that soy consumption as a whole may also improve bone health. A large cohort study of approximately 75,000 women (40-70 years of age) compared the association of soy food consumption and the risk of fractures. An inverse relationship was found between consumption of soy and the number of fractures, even after adjustment for age, major risk factors and other dietary variables. This study also reported the positive effects of soy were even more pronounced among women in early menopause. This is in agreement with many other studies also proposing that the beneficial effects of soy on bone health may be life-stage specificâ€”perio-menopausal or early menopausal women appear to be more receptive to the therapeutic effects of soy. Considering that the rate of bone loss is greatest in the first years of menopause, increased soy intake may be advisable during these years.
Other Dietary FactorsOf course, a healthy bone diet also includes avoidance or moderation of certain dietary factors. Dr. Susan Brown, author of Better Bones, Better Body, calls these “bone robbers.” Bone robbers include excessive protein, caffeine, alcohol, cola drinks and sodium. Dr. Brown, a medical anthropologist and certified clinical nutritionist, also states that a poor diet is not the only cause of osteoporosis. From a cross-cultural perspective, “A more realistic conception of the cause of osteoporosis is that of varied bone-depleting factors, each building one upon the other. Each bone-depleting factor adds to the others until the total load is more than our bone can bear.” No pun intended.
References:1 Knapen, MH, et al., 2007. Vitamin K2 supplementation improves hip bone geometry and bone strength indices in postmenopausal women. Osteoporosis International. Feb 8; [Epub ahead of print].
2 Schurgers, LJ, et al., 2007. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 109(8):3279-83.
3 Tucker, K, et al., 2005. Low plasma vitamin B12 is associated with lower BMD: The Framingham Osteoporosis Study. Journal of Bone and Mineral Research. 20:152-158.
4 Tucker, KL., et al., 2006. Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study. 84(4):936-42.
5 Jugdaohsingh R., et al., 2007. Silicon and bone health. Journal of Nutrition, Health and Aging. 11(2):99-110.
6 Abrams, SA, et al., 2005. A combination of prebiotic short-and long-chain inulin type fructan enhances calcium absorption and bone mineralization in young adolescents. American Journal of Clinical Nutrition. 82(2):471-6.
7 Holloway, L, et al., 2007. Effects of oligofructose-enriched inulin on intestinal absorption of calcium and magnesium and bone turnover markers in postmenopausal women. British Journal of Nutrition. 97(2):365-72.
8 Wu, J, et al., 2007. Possible role of equol status in the effects of isoflavones on bone and fat mass in postmenopausal Japanese women: a double-blind, randomized, controlled trial. Menopause. April 25: [Epub ahead of print].
9 Ma, DF, et al., 2007. Soy isoflavone intake inhibits bone resorption and stimulates bone formation in menopausal women: meta-analysis of randomized controlled trials. European Journal of Clinical Nutrition. March 28: [Epub ahead of print]
10 Cheong, JM, et al., 2007. Soy isoflavones do not affect bone resorption in postmenopausal women: a dose-response study using a novel approach with 41Ca. Journal of Clinical Endocrinology Metabolism. 92(2):577-82.
11 Zhang, X, et al. 2005. Prospective cohort study of soy food consumption and risk of bone fracture among postmenopausal women. Archives of Internal Medicine. 165(16):1890-5.