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Review: Vitamin K2 (MK-4) Monotherapy Modestly Increases Bone Density and Reduces Fractures in Eight Studies

Abstract

Vitamin k2 therapy for postmenopausal osteoporosis.

Vitamin K may play an important role in the prevention of fractures in postmenopausal women with osteoporosis. Menatetrenone is the brand name of a synthetic vitamin K2 that is chemically identical to menaquinone-4. The present review study aimed to clarify the effect of menatetrenone on the skeleton in postmenopausal women with osteoporosis, by reviewing the results of randomized controlled trials (RCTs) in the literature. RCTs that investigated the effect of menatetrenone on bone mineral density (BMD), measured by dual-energy X-ray absorptiometry and fracture incidence in postmenopausal women with osteoporosis, were identified by a PubMed search for literature published in English. Eight studies met the criteria for RCTs. Small RCTs showed that menatetrenone monotherapy decreased serum undercarboxylated osteocalcin (ucOC) concentrations, modestly increased lumbar spine BMD, and reduced the incidence of fractures (mainly vertebral fracture), and that combined alendronate and menatetrenone therapy enhanced the decrease in serum ucOC concentrations and further increased femoral neck BMD. This review of the literature revealed positive evidence for the effects of menatetrenone monotherapy on fracture incidence in postmenopausal women with osteoporosis. Further studies are required to clarify the efficacy of menatetrenone in combination with bisphosphonates against fractures in postmenopausal women with osteoporosis.

Iwamoto J
Nutrients 2014
PMID: 24841104 | Free Full Text

One interesting passage from the full text talks about the unpublished dose range study from Japan:

Orimo, H., et al. “Clinical evaluation of soft capsule menatetrenone (Ea-0167) in the treatment of osteoporosis: late phase II dose study.” J New Remedies Clinics 41 (1992): 1249-79.

A dose-finding study of menatetrenone in Japan [7] administered daily doses of 15, 45, 90, and 135 mg and revealed that 45 mg was the minimum effective dose for improving bone mass parameters evaluated by microdensitometry and/or single photon absorptiometry in postmenopausal women with osteoporosis. This optimal dose (45 mg/day) for the treatment of osteoporosis is about 150–180 times greater than the recommended daily dietary intake of vitamin K (250–300 μg) [8]. No toxic effects of menatetrenone (45 mg/day) have been reported [7]. High-dose vitamin K is needed to prevent fractures in postmenopausal women with osteoporosis [9]. However, the effect of menatetrenone on the skeleton remains a matter of controversy [10–17], and the role of menatetrenone in the treatment of osteoporosis therefore needs to be clarified.

High Omega-6:Omega-3 Ratios Increase Fracture Risk and Doubles Risk for Ratios > 6

Abstract

The association of red blood cell n-3 and n-6 fatty acids with bone mineral density and hip fracture risk in the women’s health initiative.

Omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFA) in red blood cells (RBCs) are an objective indicator of PUFA status and may be related to hip fracture risk. The primary objective of this study was to examine RBC PUFAs as predictors of hip fracture risk in postmenopausal women. A nested case-control study (n = 400 pairs) was completed within the Women’s Health Initiative (WHI) using 201 incident hip fracture cases from the Bone Mineral Density (BMD) cohort, along with 199 additional incident hip fracture cases randomly selected from the WHI Observational Study. Cases were 1:1 matched on age, race, and hormone use with non-hip fracture controls. Stored baseline RBCs were analyzed for fatty acids using gas chromatography. After removing degraded samples, 324 matched pairs were included in statistical analyses. Stratified Cox proportional hazard models were constructed according to case-control pair status; risk of fracture was estimated for tertiles of RBC PUFA. In adjusted hazard models, lower hip fracture risk was associated with higher RBC α-linolenic acid (tertile 3 [T3] hazard ratio [HR]: 0.44; 95% confidence interval [CI], 0.23-0.85; p for linear trend 0.0154), eicosapentaenoic acid (T3 HR: 0.46; 95% CI, 0.24-0.87; p for linear trend 0.0181), and total n-3 PUFAs (T3 HR: 0.55; 95% CI, 0.30-1.01; p for linear trend 0.0492). Conversely, hip fracture nearly doubled with the highest RBC n-6/n-3 ratio (T3 HR: 1.96; 95% CI, 1.03-3.70; p for linear trend 0.0399). RBC PUFAs were not associated with BMD. RBC PUFAs were indicative of dietary intake of marine n-3 PUFAs (Spearman’s rho = 0.45, p < 0.0001), total n-6 PUFAs (rho = 0.17, p < 0.0001) and linoleic acid (rho = 0.09, p < 0.05). These results suggest that higher RBC α-linolenic acid, as well as eicosapentaenoic acid and total n-3 PUFAs, may predict lower hip fracture risk. Contrastingly, a higher RBC n-6/n-3 ratio may predict higher hip fracture risk in postmenopausal women.

Orchard TS, Ing SW, Lu B, Belury MA…
J. Bone Miner. Res. Mar 2013
PMID: 23018646 | Free Full Text

The full text has a nice chart showing the hazard ratios for the various fatty acids they looked at.

The Omega-6:Omega-3 ratios and their respective hazard ratios were:

Omega-6:Omega-3 Ratio 1.48–5.00 5.01–6.07 6.08–10.59
Hazard Ratio 1.00 1.28 (0.71–2.30) 1.96 (1.03–3.70)

[Hazard Ratios] for hip fracture by tertiles of RBC FAs with multivariate adjustment for risk factors per Robbins and colleagues37 are reported in Table 3. No significant associations were found between RBC total SFA, MUFA, or PUFA and risk of hip fracture. However, there was a significant inverse linear association between hip fracture risk and total n-3 FAs in RBCs (p for linear trend 0.0492). When examining individual n-3 FAs, there was a 56% lower relative risk of hip fracture with highest RBC ALA (tertile 3 [T3] hazard ratio [HR]: 0.44; 95% CI, 0.23–0.85; p for linear trend 0.0154), and a 54% lower hip fracture risk with highest EPA levels (T3 HR: 0.46; 95% CI, 0.24–0.87; p for linear trend 0.0181) compared to T1. Neither DHA nor the n-3 index was significantly associated with risk of fracture. In contrast, hip fracture risk nearly doubled in women in the highest tertile of the n-6/n-3 FA ratio (HR T3: 1.96; 95% CI, 1.03–3.70; p for linear trend 0.0399). Because the n-6/n-3 FA ratio in RBCs primarily reflects the ratio of AA to EPA and DHA, we further examined the relation of the AA/EPA + DHA ratio to hip fracture risk. Similar to the n-6/n-3 FA ratio, a higher AA/EPA + DHA ratio produced higher HR for hip fracture, but the association was not significant (T3 HR: 1.69; 95% CI, 0.86–3.31; p for linear trend 0.1242). Although the direction of association between total n-6 FAs, AA, and hip fracture was toward harm, there was no significant relation of either total n-6 FAs or AA with hip fracture. There was an inverse direction of association between LA and hip fracture risk, but again, this was not statistically significant (T3 HR: 0.77; 95% CI, 0.40–1.49; p for linear trend 0.5140). Inclusion of additional potential confounders (alcohol consumption, total energy intake, total calcium intake, total vitamin D intake, and multivitamin use) in the model produced similar results….

Vitamin K2 (menatetrenone) effectively prevents fractures and sustains lumbar bone mineral density in osteoporosis.

Abstract

Vitamin K2 (menatetrenone) effectively prevents fractures and sustains lumbar bone mineral density in osteoporosis.

We attempted to investigate whether vitamin K2 (menatetrenone) treatment effectively prevents the incidence of new fractures in osteoporosis. A total of 241 osteoporotic patients were enrolled in a 24-month randomized open label study. The control group (without treatment; n = 121) and the vitamin K2-treated group (n = 120), which received 45 mg/day orally vitamin K2, were followed for lumbar bone mineral density (LBMD; measured by dual-energy X-ray absorptiometry [DXA]) and occurrence of new clinical fractures. Serum level of Glu-osteocalcin (Glu-OC) and menaquinone-4 levels were measured at the end of the follow-up period. Serum level of OC and urinary excretion of deoxypyridinoline (DPD) were measured before and after the treatment. The background data of these two groups were identical. The incidence of clinical fractures during the 2 years of treatment in the control was higher than the vitamin K2-treated group (chi2 = 10.935; p = 0.0273). The percentages of change from the initial value of LBMD at 6, 12, and 24 months after the initiation of the study were -1.8 +/- 0.6%, -2.4 +/- 0.7%, and -3.3 +/- 0.8% for the control group, and 1.4 +/- 0.7%, -0.1 +/- 0.6%, and -0.5 +/- 1.0% for the vitamin K2-treated group, respectively. The changes in LBMD at each time point were significantly different between the control and the treated group (p = 0.0010 for 6 months, p = 0.0153 for 12 months, and p = 0.0339 for 24 months). The serum levels of Glu-OC at the end of the observation period in the control and the treated group were 3.0 +/- 0.3 ng/ml and 1.6 +/- 0.1 ng/ml, respectively (p < 0.0001), while the serum level of OC measured by the conventional radioimmunoassay (RIA) showed a significant rise (42.4 +/-6.9% from the basal value) in the treated group at 24 months (18.2 +/- 6.1% for the controls;p = 0.0081). There was no significant change in urinary DPD excretion in the treated group. These findings suggest that vitamin K2 treatment effectively prevents the occurrence of new fractures, although the vitamin K2-treated group failed to increase in LBMD. Furthermore, vitamin K2 treatment enhances gamma-carboxylation of the OC molecule.

Shiraki M, Shiraki Y, Aoki C, Miura M
J. Bone Miner. Res. Mar 2000
PMID: 10750566

 

I don’t know why they had to say “the vitamin K2-treated group failed to increase in LBMD”, when they could have said the vitamin K2-treated group prevented the decrease in LBMD seen in the control group, or that LBMD was increased compared to controls.

Vitamin K2 (MK-4) Prevents Glucocorticoid Bone Loss

Abstract

Vitamin K2 inhibits glucocorticoid-induced bone loss partly by preventing the reduction of osteoprotegerin (OPG).

We have recently demonstrated that glucocorticoid (GC) suppresses bone formation and enhances bone resorption, with resultant bone loss. This altered bone turnover is not due to the action of parathyroid hormone (PTH), but appears to be related to the suppression of osteoprotegerin (OPG). As vitamin K2 (menatetrenone) has been used for the treatment of osteoporosis, the present study was carried out to evaluate the effect of vitamin K2 on GC-induced bone loss. Twenty patients with chronic glomerulonephritis treated with GC for the first time were chosen for this study. Ten patients received GC alone (group A) and the other 10 patients each received 15 mg of vitamin K2 per day in addition to GC (group B). Markers of bone metabolism, including serum OPG, osteocalcin (OC), bone-specific alkaline phosphatase activity (BAP), PTH, tartrate-resistant acid phosphatase (TRAP), and bone mineral density (BMD), were measured before and during the treatment. OPG was significantly decreased in group A (P < 0.001), while no significant change was seen in group B. TRAP was markedly increased in both groups, more particularly in group A (P < 0.01). PTH was decreased in group A, but was increased in group B. OC was decreased at month 1 but subsequently increased until month 12 in both groups. BAP had decreased at month 3 in group A (P < 0.05), but not in group B. BMD of the lumbar spine was significantly reduced after 6 months (P < 0.01), and 12 months (P < 0.001) of treatment in group A, whereas there was no remarkable change in group B. The present study demonstrated that the inhibition exerted by vitamin K2 of the reduction in OPG induced by GC may, at least in part, play a role in the prevention and treatment of GC-induced bone loss.

Sasaki N, Kusano E, Takahashi H, Ando Y…
J. Bone Miner. Metab. 2005
PMID: 15616893 | Free Full Text

The dose in the abstract is wrong. They used 15mg three times per day. That is 45mg per day and the same as the prescription dose used in Japan.

The patients were randomly divided into two groups before treatment. Informed consent was obtained from all subjects. Ten patients (6 men, and 2 premenopausal and 2 postmenopausal women ) received GC alone (group A) and the other 10 patients (6 men and 2 premenopausal and 2 postmenopausal women) each received 15 mg of vitamin K2 (menatetrenone; Glakay; Eisai, Tokyo, Japan) three times per day in addition to GC (group B) during the study period. The profiles of the patients are shown in Table 1. Renal function was normal in all subjects (serum Cr level 1.2mg/dl). There were no significant differences between the two groups in age, body mass index, or dose of GC (Table 1), or in various serum and urinary biochemical parameters at baseline (Table 2).

 

MK-7 Suppresses Osteoblast Proliferation and Enhances RANKL In Vitro

Abstract

Menaquinone-7 regulates the expressions of osteocalcin, OPG, RANKL and RANK in osteoblastic MC3T3E1 cells.

Epidemiological studies show that dietary intake of natto, which contains significant amount of vitamin K(2), reduces the risk of bone formation loss. However, many confounding factors, such as calcium and isoflavone, are found in natto, because it is made from soybeans. In this study, the direct effects of MK-7, a vitamin K(2) analogue, were assessed in osteoblasts. Osteoblastic MC3T3E1 cells were cultured with or without MK-7 for 10 days and the number of cells was calculated. The cell count was not different between MK-7 treated cells and control cells for 1, 2, and 4 days. However, it was significantly suppressed in MK-7 treated cells at 10 days, suggesting that MK-7 suppressed cell proliferation. Real-time PCR analysis showed that mRNAs of osteocalcin (OC), osteoprotegerin (OPG), and the receptor activator of the NFkappaB ligand (RANKL) were induced after MK-7 administration to the culture medium. RANK mRNA expression was also enhanced by MK-7 administration. Immunocytochemical analysis showed that MK-7 increased the protein levels of OC and RANKL. RANK protein was also enhanced, but this induction was suppressed by anti-RANK antibody administration. This suppression was recovered when anti-RANK antibody and MK-7 were administered. These observations suggest that MK-7 may directly affect MC3T3E1 cells and stimulate osteoblastic differentiation, not proliferation. Katsuyama H, Otsuki T, Tomita M, Fukunaga M… Int. J. Mol. Med. Feb 2005 PMID: 15647836

MK-7 does some bad things. This says it supresses poliferation of osteoblasts, and enhances RANKL. This is in vitro and there were positive effects as well. This is interesting, but in vivo studies would be good to look at.

Review: Vitamin K and Bone Health 1998-2008

Abstract

Update on the role of vitamin K in skeletal health.

A protective role for vitamin K in bone health has been suggested based on its role as an enzymatic cofactor. In observational studies, vitamin K insufficiency is generally associated with lower bone mass and increased hip fracture risk. However, these findings are not supported in randomized controlled trials (RCT) of phylloquinone (vitamin K(1)) supplementation and bone loss at the hip in the elderly. This suggests that increased vegetable and legume intakes may simultaneously improve measures of vitamin K status and skeletal health, even though the mechanisms underlying these improvements may be independent of each other. Menaquinone-4 (vitamin K(2)), when given at pharmacological doses, appears to protect against fracture risk and bone loss at the spine. However, there are emerging data that suggest the efficacy of vitamin K supplementation on bone loss is inconclusive.

Shea MK, Booth SL
Nutr. Rev. Oct 2008
PMID: 18826451 | Free Full Text

This is a great review of the different forms of Vitamin K and their benefits for bone. The full study includes a table listing many studies dated from 1998 to 2008 with their outcomes. I highly recommend reading the full text.

MK-4 in doses of 45 mg/d is used as a pharmacological treatment for osteoporosis in Japan, so there are numerous randomized control studies that have assessed the efficacy of MK-4 supplementation on skeletal health. Such doses cannot be attained from the diet, regardless of the form of vitamin K consumed. Phylloquinone from the diet is converted to MK-4 in certain tissues, including bone, but the proportion of phylloquinone that is converted is not known and no dose-dependent data are available for this conversion.

[…]

As reviewed in an earlier volume of this journal,60 studies indicate a therapeutic dose (45 mg/day) of MK-4 has a beneficial effect on spine or metacarpal BMD and fracture61–76 (Table 2). There is also improvement in bone turnover, as measured by circulating markers of bone formation and bone resorption, in response to MK-4 supplementation studies.71,72,76,77 In a separate systematic review and analysis of randomized clinical trials assessing the influence of vitamin K supplementation on hip fracture, Cockayne et al.78 concluded that supplementation with MK-4 for longer than 6 months reduces risk for hip and vertebral fracture. Included in that analysis were 12 studies that used daily doses of 45 mg/d of MK-4. As discussed by the authors, several of the studies used for the meta-analysis lacked sufficient sample size,64–66,70,73,79 were non-placebo-controlled intervention trials,70–74,76,77,80 and/or used concurrent treatment with calcium and/or vitamin D.62,69,75,76

It was subsequently disclosed that a large unpublished surveillance study conducted in Japan (n > 3000) did not find a protective effect of MK-4 supplementation (45 mg/day) on bone loss and fracture in the elderly, and that inclusion of this study may have altered the results of the meta-analysis.81 More recently, two placebo-controlled studies with large sample sizes reported no protective effect of 45 mg/d of MK-4 on hip BMD.59,67 Prior to these two publications, the majority of MK-4 supplementation studies did not report hip BMD as an outcome (Table 2). Given the heterogeneous quality of the studies used and considering the null findings of more recent, larger, placebo-controlled trials and unpublished surveillance data, prior systematic reviews and meta-analyses may need to be revisited.

 

Calcium Threonate in Ester-C Enhances Vitamin C’s Bone Mineralization In Vitro

Abstract

Enhanced production of mineralized nodules and collagenous proteins in vitro by calcium ascorbate supplemented with vitamin C metabolites.

Vitamin C or ascorbate is important in wound healing due to its essential role in collagen synthesis. To study wound healing in the periodontium, cells adherent to expanded polytetrafluoroethylene (ePTFE) augmentation membranes, recovered from edentulous ridge augmentation procedures, have been established in culture in our laboratories. The objective of this study was to determine whether treatment of these cells with a calcium ascorbate, which contains vitamin C metabolites (metabolite-supplemented ascorbate), would increase the production of collagenous protein and mineralized tissue in vitro, as compared to unsupplemented calcium ascorbate (ascorbate).
Cells derived from ePTFE membranes were cultured with beta-glycerophosphate and the test agents for 2 to 5 weeks, and the surface areas of the cell cultures occupied by mineralized nodules were measured using computerized image analysis. One experiment tested the effects of calcium threonate, one of the vitamin C metabolites in metabolite-supplemented ascorbate. Incorporation of radioactive proline and glycine was used as a measure of total protein (radioactivity precipitated by trichloracetic acid) and collagenase-digestible protein (radioactivity released by collagenase digestion.) Co-localization of collagen and fibronectin was examined by immunofluorescence.
In vitro treatment of these cells with metabolite-supplemented ascorbate increased the area of the cell cultures occupied by mineralized nodules after 5 weeks. Cell cultures treated with metabolite-supplemented ascorbate also exhibited significant increases in total protein. The increase in collagenous proteins in these cultures accounted for 85% of the increase in total protein. The greatest difference between treatment groups was observed in the cell-associated fraction containing the extracellular matrix. The additional collagen exhibited normal co-distribution with fibronectin. In cultures treated with ascorbate spiked with calcium threonate, the area of mineralized tissue was significantly greater than in ascorbate-treated cultures, but was less than that observed in cultures treated with metabolite-supplemented ascorbate.
In vitro treatment with ascorbate containing vitamin C metabolites enhanced the formation of mineralized nodules and collagenous proteins. Calcium threonate may be one of the metabolites influencing the mineralization process. Identifying factors which facilitate the formation of mineralized tissue has significant clinical ramifications in terms of wound healing and bone regeneration.

Rowe DJ, Ko S, Tom XM, Silverstein SJ…
J. Periodontol. Sep 1999
PMID: 10505801

This study is on Ester-C. Ester-C, PureWay-C, and AlphaSorb-C are Vitamin C products that contain Calcium-L-Threonate. Biocalth is Calcium product which is all Calcium-L-Threonate without Vitamin C.

 

Review: Low Protein Intake and Bones – 2003

Abstract

Low protein intake: the impact on calcium and bone homeostasis in humans.

Increasing dietary protein results in an increase in urinary calcium. Despite over 80 y of research, the source of the additional urinary calcium remains unclear. Because most calcium balance studies found little effect of dietary protein on intestinal calcium absorption, it was assumed that the skeleton was the source of the calcium. The hypothesis was that the high endogenous acid load generated by a protein-rich diet would increase bone resorption and skeletal fracture. However, there are no definitive nutrition intervention studies that show a detrimental effect of a high protein diet on the skeleton and the hypothesis remains unproven. Recent studies from our laboratory demonstrate that dietary protein affects intestinal calcium absorption. We conducted a series of short-term nutrition intervention trials in healthy adults where dietary protein was adjusted to either low, medium or high. The highest protein diet resulted in hypercalciuria with no change in serum parathyroid hormone. Surprisingly, within 4 d, the low protein diet induced secondary hyperparathyroidism that persisted for 2 wk. The secondary hyperparathyroidism induced by the low protein diet was attributed to a reduction in intestinal calcium absorption (as assessed by dual stable calcium isotopes). The long-term consequences of these low protein-induced changes in calcium metabolism are not known, but they could be detrimental to skeletal health. Several recent epidemiological studies demonstrate reduced bone density and increased rates of bone loss in individuals habitually consuming low protein diets. Therefore, studies are needed to determine whether low protein intakes directly affect rates of bone resorption, bone formation or both.

Kerstetter JE, O’Brien KO, Insogna KL
J. Nutr. Mar 2003
PMID: 12612169 | Free Full Text

The subject is complicated with a lot of conflicting data. The full article is great.

When BMD is the primary outcome, most (39–48), but not all (49–53), epidemiological studies show a positive relationship between protein intake and BMD. Stated another way, most of the epidemiological evidence shows that when other known dietary factors are controlled, those individuals who consume low protein diets have lower BMD. Using the National Health and Nutrition Examination Survey (NHANES) III database, we found that in 1882 non-Hispanic white women 50 y old and older, after adjusting for age and body weight, a low protein intake was associated with a significantly lower hip bone mineral density (Fig. 5) (47). Consistent with these data, Hannan and colleagues (46) studied 615 participants in the Framingham Osteoporosis Study over a 4-y period and found that lower levels of protein intake were associated with significantly higher rates of bone loss at the hip and spine. These findings confirm the earlier work of Freudenheim et al. (39), who reported that a low protein intake was associated with greater loss in bone density from the wrist in 35- to 65-y-old women. Most recently, Promislow et al. (48) found a positive association between total dietary protein intake and BMD in elderly men and women participating in the Rancho Bernardino study. Therefore, there is substantial agreement in those studies in which BMD is the primary outcome. Munger et al. (59), reporting data from the Iowa Women’s Health Study, found an increased risk of hip fracture in 55- to 69-y-old women consuming the lowest amounts of protein.

Adequate dietary protein may also help in fracture healing and in preventing bone loss after fracture. Bonjour and colleagues (73) studied the effects of 6 mo of protein supplementation, after osteoporotic hip fracture, in a group of elderly subjects. These patients had self-selected protein intakes that were very low (∼40 g). The administration of additional protein (+20 g) was associated with significant attenuation of proximal femur bone loss in the fractured hip such that, at 1 y, bone loss rates were 50% lower in the protein-supplemented individuals. The correction of poor protein nutrition also improved serum prealbumin and insulin-like growth factor 1 (IGF-1) concentrations and decreased the length of rehabilitation (73).

There is agreement that diets moderate in protein (in the approximate range of 1.0 to 1.5 g protein/kg) are associated with normal calcium metabolism and presumably do not alter skeletal homeostasis. Approximately 30–50% of adults in the United States consume dietary protein that could be considered moderate. At low protein intakes, intestinal calcium absorption is reduced, resulting in increases in serum PTH and calcitriol that persist for at least 2–4 wk. The long-term implications of these findings are unknown; however, recent epidemiological data suggest increased rates of bone loss in individuals consuming such diets. Individuals consuming high protein intakes, particularly from omnivorous sources, develop hypercalciuria that is attributable for the most part to an increase in intestinal calcium absorption. Whether high protein diets result in an increase in bone resorption and higher fracture rates remains uncertain.

 

Potassium Citrate Increases Bone Density and Volume in Adults

Abstract

Effect of potassium citrate on bone density, microarchitecture, and fracture risk in healthy older adults without osteoporosis: a randomized controlled trial.

The acid load imposed by a modern diet may play an important role in the pathophysiology of osteoporosis. Our objective was to evaluate the skeletal efficacy and safety and the effect on fracture prediction of K-citrate to neutralize diet-induced acid loads.
We conducted a randomized, double-blind, placebo-controlled trial at a teaching hospital.
Subjects included 201 elderly (>65 yr old) healthy men and women (t-score of -0.6 at lumbar spine).
Intervention was 60 mEq of K-citrate daily or placebo by mouth. All subjects received calcium and vitamin D.
The primary outcome was change in areal bone mineral density (aBMD) at the lumbar spine by dual-energy x-ray absorptiometry after 24 months. Secondary endpoints included changes in volumetric density and microarchitectural parameters by high-resolution peripheral quantitative computed tomography in both radii and both tibiae and fracture risk assessment by FRAX (Switzerland).
K-citrate increased aBMD at lumbar spine from baseline by 1.7 ± 1.5% [95% confidence interval (CI) = 1.0-2.3, P < 0.001] net of placebo after 24 months. High-resolution peripheral quantitative computed tomography-measured trabecular densities increased at nondominant tibia (1.3 ± 1.3%, CI = 0.7-1.9, P < 0.001) and nondominant radius (2.0 ± 2.0%, CI = 1.4-2.7, P < 0.001). At nondominant radius, trabecular bone volume/tissue volume increased by 0.9 ± 0.8%, (CI = 0.1-1.7), trabecular thickness by 1.5 ± 1.6% (CI = 0.7-2.3), and trabecular number by 1.9 ± 1.8% (CI = 0.7-3.1, for all, P < 0.05). K-citrate diminished fracture prediction score by FRAX significantly in both sexes.
Among a group of healthy elderly persons without osteoporosis, treatment with K-citrate for 24 months resulted in a significant increase in aBMD and volumetric BMD at several sites tested, while also improving bone microarchitecture. Based on the effect on fracture prediction, an effect on future fractures by K-citrate is possible.

Jehle S, Hulter HN, Krapf R
J. Clin. Endocrinol. Metab. Jan 2013
PMID: 23162100

Despite the conflicting evidence for the acid load theory, potassium or citrate nonetheless appear to increase bone density. How it does that is debated.

Review: Potassium and Osteoporosis

Abstract

Potassium and health.

Potassium was identified as a shortfall nutrient by the Dietary Guidelines for Americans 2010 Advisory Committee. The committee concluded that there was a moderate body of evidence of the association between potassium intake and blood pressure reduction in adults, which in turn influences the risk of stroke and coronary heart disease. Evidence is also accumulating of the protective effect of adequate dietary potassium on age-related bone loss and reduction of kidney stones. These benefits depend on organic anions associated with potassium as occurs in foods such as fruits and vegetables, in contrast to similar blood pressure-lowering benefits of potassium chloride. Benefits to blood pressure and bone health may occur at levels below current recommendations for potassium intake, especially from diet, but dose-response trials are needed to confirm this. Nevertheless, intakes considerably above current levels are needed for optimal health, and studies evaluating small increases in fruit and vegetable intake on bone and heart outcomes for short periods have had disappointing results. In modern societies, Western diets have led to a decrease in potassium intake with reduced consumption of fruits and vegetables with a concomitant increase in sodium consumption through increased consumption of processed foods. Consumption of white vegetables is associated with decreased risk of stroke, possibly related to their high potassium content. Potatoes are the highest source of dietary potassium, but the addition of salt should be limited. Low potassium-to-sodium intake ratios are more strongly related to cardiovascular disease risk than either nutrient alone. This relationship deserves further attention for multiple target tissue endpoints.

Weaver CM
Adv Nutr May 2013
PMID: 23674806 | Free Full Text

The full text includes several pages about osteoporosis. This is just the final summary at the end of that section:

In summary, benefits of potassium on bone are seen typically when given as organic salts at relatively high doses of 60 to 90 mmol/d (2400–3600 mg/d). Organic salts of potassium reduce urinary calcium loss and improve calcium balance at these levels. But whether that is related to protection against skeletal buffering of an acidogenic diet is still a topic for debate. Perhaps acid-base balance is not the mechanism in healthy kidneys, but as kidney function declined with age, it may be an important mechanism. The glomerular filtration rate declines by as much as 50% from age 20 to 80 y (68), or perhaps excess acid only affects bone through interaction with receptors on bone cells to stimulate bone turnover, and this process is reduced by the alkaline organic salts of potassium.