|Osteoporosis is a reduction in bone tissue resulting in brittle and fragile bones prone to fracture, usually occurring in postmenopausal women and elderly men (due to hormonal changes or a deficiency of calcium or vitamin D). In the first 3-5 years after menopause, women lose 3-5% of their bone mass per year. After about 10 years, bone loss tapers off only to increase again after the age of 80 (1). Isoflavones in soy (genistein and daidzein) have been found to have a modest positive effect on bone tissue in a few animal studies and two human studies. This area of research is quite new and several other human studies are currently underway.|
Some food for thought: if drinking dairy products all the time is so healthy for you, why is osteoporosis so prevalent in North America? If the vitamins and calcium in dairy are sufficient to prevent osteoporosis why is the disease so rampant here? In Asian cultures that consume perhaps 10% the dairy products and instead rely on a more varied diet that includes soyfoods, osteoporosis is virtually unknown.
The Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease was held in September of 1996. Several animal studies performed on ovariectomized rats addressed the issue of isoflavones and bone loss. One study found that isoflavones prevented but did not reverse or restore bone loss (2). Another found that genistein, at an optimal dose, resulted in retention of bone mineral mass equivalent to physiologic dose of estradiol, possibly by acting as an agonist on estrogen receptors in bone tissues. Genistein may also effect other enzymes in bone cells, such as alkaline phosphatase (3). A third study suggested that genistein inhibits osteoclasts, cells that function in the removal of bone tissue and are dependent on the enzyme tyrosine kinase, by inhibiting its activity (4). A fourth study found that treatment with 5 and 25mg, but not 1mg, of genistein decreased loss of bone mineral density and volume and concluded that the effect of genistein is via stimulation of bone formation and not suppression of bone resorption, as in the case of estrogens (5). Two human studies found significant increases in bone mineral content in the isoflavone consuming group.
The first study, done at the University of Illinois at Urbana-Champaign, involved 66 post-menopausal women, who consumed 40g per day of isolated soy protein containing either 55mg or 90mg of isoflavones for a six-month period. Those women consuming the higher level of isoflavones had an increase in bone mineral density and bone mineral content in the lumbar spine (6). In the second study, done in Australia and involving 52 post-menopausal women, those who consumed 45g of soy grits per day for a 12-week period also had a significant increase in bone mineral content in the lumbar spine (7). Abstracts from the meeting can be found at www.soyfoods.com.
More recently, John J.B. Anderson published a review entitled “The Effects of Phytoestrogens on Bone” in the journal Nutrition Research. His review, which covered published reports of epidemiological and experimental studies of humans, animal models, isolated tissues and cells in culture, concluded that isoflavones (particularly genistein and daidzein), at optimal doses, result in improved bone mass (8).
|Many people ask what amount of soy they should consume daily to protect them against bone loss. The research is still quite new and thus it is impossible to recommend a specific amount, but it is a good idea to eat soy products daily instead of taking isoflavone supplements, as it is not entirely clear at the time if isoflavones are entirely responsible for the beneficial effects.|
In general, for protection against osteoporosis, adult women should make sure they get enough calcium and Vitamin D in their diet and engage in weight-bearing exercise daily. In August of 1997 the Institute of Medicine of the National Academy of Sciences issued a report stating that both men and women ages 19-50 should consume 1,000 mg of calcium per day and those over 50 years should consume 1,200 mg per day (9). Some people have asked if calcium and soy can be taken together. Some plants, like soy, contain substances such as phytate and oxalate that bind minerals such as calcium which prevents or reduces absorption. However, bioavailability data on calcium indicate that absorption from tofu and soy is similar to milk. Also, soy is relatively high in calcium. Thus, it is fine to take calcium supplements with soy products for maximum osteoporosis prevention.
References 2-7 all presented at the Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, Belgium, September, 1996.
This information provided by Dr. Clare M. Hasler.