Table 5.

Summary of human studies.

Probiotics	Study Design	Mechanism Findings	Ref
7 bacteria species (Lactobacillus casei, Bifidobacterium longum, Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus bulgaricus, Bifidobacterium breve, and Streptococcus thermophilus)	This randomized, double-blind placebo-controlled clinical trial was performed on 50 patients with osteopenia aged 50–72. Participants were randomly assigned to take either a multispecies probiotic supplement (GeriLact; n D 25) or placebo (n D 25) for six months.	Various strains of probiotics on bone may produce several short-chain fatty acids, which decrease PTH, followed by an increase in mineral absorption by solubilization. Probiotic administration reduces the expression of several proinflammatory and osteolytic cytokines (TNF-a and IL-1b).	[64]
Lactobacillus paracasei DSM 13434, Lactobacillus plantarum DSM 15312, and Lactobacillus plantarum DSM 15313	Early postmenopausal women were randomized to receive three Lactobacillus strains (1 × 101⁰ CFU/capsule) or placebo once daily for 12 months.	The bone protective effect of probiotics reduces gut permeability, increases short-chain fatty acids, reduces inflammation in the gut, reduces levels of proinflammatory cytokines in bone, and decreases osteoclastic bone resorption.	[65]
Lactobacillus reuteri ATCCPTA 6475	In this double-blind, placebo-controlled study, women aged 75 to 80 with low BMD were randomized to orally receive 1010 colony-forming units of L. reuteri 6475 daily or placebo. The predefined primary end-point was a relative change after 12 months in tibia total volumetric BMD (vBMD).	L. reuteri 6475 for 12 months reduced loss of tibia total vBMD in older women with low BMD. The underlying mechanism for this has not been elucidated, and further studies are needed to evaluate this strain supplementation’s clinical usefulness.	[66]
Bacillus subtilis C-3102	76 healthy postmenopausal Japanese women were treated with a placebo or probiotic B. subtilis C-3102 spore-containing tablets for 24 weeks.	C-3102 improves BMD by inhibiting bone resorption and modulating gut microbiota in healthy postmenopausal women.	[67]
Isoflavones	Study Design	Mechanism Findings	Ref
Red clover extract (RCE) rich in isoflavone aglycones and probiotics (lactic acid bacteria)	A 12-month, double-blind, parallel design, placebo-controlled, randomized controlled trial of 78 postmenopausal osteopenic women supplemented with calcium (1200 mg/d), magnesium (550 mg/d), and calcitriol (25 mg/d) given either 60 mg isoflavone aglycones/d and probiotics (RCE) or a masked placebo (CON)	Twice-daily RCE intake over one year attenuated BMD loss caused by estrogen deficiency, improved bone turnover, promoted a favorable estrogen metabolite profile (2-OH:16a-OH), and stimulated equol production in postmenopausal women with osteopenia.	[68]
Daidzein, genistein, and glycitein	99 healthy premenopausal women were randomized to isoflavones (136.6 mg aglycone equivalence) and 98 to placebo for five days per week for up to two years. BMD, serum calcium and urinary excretion of daidzein and genistein were measured before and during treatment.	Isoflavone exposure interacted with serum calcium in affecting whole-body BMD, but not hip and spine BMD.	[69]
Genistein, daidzein, and glycitein	A double-blind, randomized controlled trial in healthy postmenopausal women (46–63 yr) were studied. There were two soy isoflavone doses (80 or 120 mg/d) vs. placebo tablets on volumetric bone mineral density and strength (using peripheral quantitative computed tomography)	Soy isoflavone exerted a modest beneficial effect on the percentage change in the midshaft femur vBMD as TLMP increased and a modest beneficial effect on the midshaft femur SSI as bone turnover (reflected by serum BAP) increased.	[70]
Soy isoflavone, calcium, and soy isoflavone combined with calcium	160 women with osteoporosis or osteopenia were enrolled and randomized into four groups, namely control, soy isoflavone, calcium, and soy isoflavone combined with calcium.	Isoflavone combined with calcium increases estradiol level and reduces osteocalcin level, while increasing plasma calcium concentration.	[71]
Daidzein and genistein and green kiwifruit	33 healthy postmenopausal Caucasian women were randomly allocated to two groups: Group A received isoflavones for the first six weeks, followed by isoflavones and kiwifruit for the following six weeks. Group B had the same intervention sequence in reverse. Isoflavone capsules and kiwifruit were taken in the morning with breakfast.	Osteocalcin (OC) is a vitamin K-dependent protein produced by the osteoblasts and is the primary noncollagenous protein in bone. Vitamin K acts as an essential cofactor for the enzymatic carboxylation of OC’s glutamyl side chains.	[72]