Soy boosts bone density in menopausal women
NutraIngredients.com - Increased soy isoflavone consumption from dietary or supplemental sources for six months can boost bone mineral density in the spine by almost one gram in menopausal women, according to a meta-analysis of 10 randomised controlled trials.
A total of 608 subjects provided data for the analysis, which reported the favourable effects were significant with consumption of more than 90 mg of isoflavones per day.
The results are published on-line in the journal Clinical Nutrition.
Previous studies have reported conflicting results concerning soy isoflavones (40 to 99 mg/d doses) and bone health for postmenopausal women. But the new meta-analysis adds to the debate by reporting that such doses of soy isoflavones (less than 90 mg/d) may improve bone density.
Previous studies from China have linked soy isoflavones to increases in bone mineral density (BMD), while a recent large study in the Archives of Internal Medicine (2005, Vol. 165, pp. 1890-1895) reported that high soy consumption was linked with a 48 per cent decrease in fractures for women who had been menopausal for less than 10 years
The intake of isoflavones varied greatly amongst the trials used for the new meta-analysis, ranging from 4.4 to 150 mg/day, while trial duration also ranged from three to 24 months, state the researchers from Peking University (China), University of Yamanashi (Japan), Soochow University (China).
Lead author De-Fu Ma reports that isoflavone consumption was associated with a 20.6 mg per sq. cm increase in spine bone mineral density (SBMD), compared to subjects consuming placebo.
Moreover, isoflavone intake of more than 90 mg/day and lasting at least six months was associated with a 28.5 and 27 mg per sq. cm increased in SBMD, respectively.
In addition, the spine bone mineral content (SBMC) was 0.93 grams higher on average in subjects taking isoflavones, compared to placebo.
“The mechanism of the SBMD-increasing effect of isoflavones is not well understood,” wrote the researchers. “Isoflavones may combine with the estrogen receptor, albeit with lower affinity than 17-beta-estradiol, and stimulate estrogen activity, thus having an estrogenic effect on bone.
“On the other hand, soy diets were shown to increase calcium absorption in rats.
“In addition, there are also some human studies reporting that isoflavones in soy protein isolate can significantly increase bone formation by stimulating serum bone-specific alkaline phosphatase synthesis or significantly decrease bone resorption by inhibiting urinary deoxypyridinoline incretion.”
“Future randomised controlled trials should include a larger sample size, use of graded isoflavone dosages and an examination of the long-term effects of isoflavone supplementation on bone mass and fracture risk,” they concluded.
Limiting bone loss in post-menopausal women could ease the burden of osteoporosis, a disease that affects half of all women over the age of 50. According to the International Osteoporosis Foundation, the total direct cost of osteoporotic fractures is €31.7 bn in Europe.
[Clinical Nutrition doi:10.1016/j.clnu.2007.10.012]
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Soy has many upsides.
There is at least one downside - too much can affect the thyroid.
For vegetarians, especially vegans, if they have problems with temperature or weight regulation it is worth getting their thyroid checked.
Thank you Evan. I’ve Googled a bit on the topic and would like to share some of the findings here.
From those argue against soy:
(http://www.thyroid-info.com/articles/soydoerge.htm)
In a February 18, 1999 official letter of protest to the FDA, Doerge and Daniel Sheehan, who at that time were the Food and Drug Administration’s (FDA) two key experts on soy, protested the health claims approved by the FDA on soy products, saying:
“there is abundant evidence that some of the isoflavones found in soy, including genistein and equol, a metabolize of daidzen, demonstrate toxicity in estrogen sensitive tissues and in the thyroid. This is true for a number of species, including humans. Additionally, isoflavones are inhibitors of the thyroid peroxidase which makes T3 and T4. Inhibition can be expected to generate thyroid abnormalities, including goiter and autoimmune thyroiditis. There exists a significant body of animal data that demonstrates goitrogenic and even carcinogenic effects of soy products. Moreover, there are significant reports of goitrogenic effects from soy consumption in human infants and adults.”
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From literature review:
Thyroid. 2006 Mar;16(3):249-58. (http://www.ncbi.nlm.nih.gov/pubmed/16571087?ordinalpos=12&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum)
Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature
Soy foods are a traditional staple of Asian diets but because of their purported health benefits they have become popular in recent years among non-Asians, especially postmenopausal women.
There are many bioactive soybean components that may contribute to the hypothesized health benefits of soy but most attention has focused on the isoflavones, which have both hormonal and nonhormonal properties.
However, despite the possible benefits concerns have been expressed that soy may be contraindicated for some subsets of the population. One concern is that soy may adversely affect thyroid function and interfere with the absorption of synthetic thyroid hormone. Thus, the purpose of this review is to evaluate the relevant literature and provide the clinician guidance for advising their patients about the effects of soy on thyroid function.
In total, 14 trials (thyroid function was not the primary health outcome in any trial) were identified in which the effects of soy foods or isoflavones on at least one measure of thyroid function was assessed in presumably healthy subjects; eight involved women only, four involved men, and two both men and women. With only one exception, either no effects or only very modest changes were noted in these trials. Thus, collectively the findings provide little evidence that in euthyroid, iodine-replete individuals, soy foods, or isoflavones adversely affect thyroid function.
In contrast, some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients.
However, hypothyroid adults need not avoid soy foods. In addition, there remains a theoretical concern based on in vitro and animal data that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase risk of developing clinical hypothyroidism. Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate.