Strontium and Bone Health

Strontium, an alkaline earth metal, has been studied for its ability to increase BMD and reduce fracture risk. Strontium ranelate (SR) is a form of strontium salt from ranelic acid patented by a French company. SR is well studied and currently approved for the osteoporosis treatment in most of Europe but is not yet approved in the United States or available as an osteoporosis supplement. Animal studies have shown it to have an affinity for bone, decreasing bone resorption and increasing bone formation in rats.1 A recent in vitro study determined that SR affects bone through induction of osteoblastogenesis.2 Several studies have evaluated the efficacy of SR in preventing and reversing osteoporosis in experimental animals and humans.

In 2002 results were published from a phase II, 2-year, randomized, multicenter, double-blind, placebo-controlled, dose-response trial of SR for the treatment of osteoporosis (STRATOS).3 Participants in the study were 353 non-obese, post-menopausal, osteoporotic women between 45 and 78 years of age who were randomized to one of 4 groups (placebo, SR 0.5 g/d, SR 1.0 g/d, and SR 2.0 g/d). In addition to supplemental strontium or placebo, all patients received supplemental calcium (500 mg/d) and vitamin D (vitamin D3, 800 IU/d) “to ensure,” as the researchers said, “that patients affected by severe osteoporosis received a minimum level of active treatment.” All women had at least 1 previous vertebral fracture (T4 to L5) and a lumbar T-score of -2.4 or less. The primary endpoint was lumbar BMD, and the secondary outcomes included femoral neck BMD (FN-BMD), incidence of new vertebral deformities, and biochemical markers of bone metabolism. Bone measurements were tested using DEXA and were verified by iliac crest bone biopsies taken at months 12 and 24.

An increase in BMD was observed in all treatment groups by 12 months, with further increases at 24 months. FN-BMD also increased in treatment groups, but decreased in the placebo group. By the end of the second year of the study, the incidence of new vertebral deformities, while having increased in the placebo group, decreased in the treatment groups. However, during the second year, women receiving 0.5 g SR/day had a 0.51 (95% CI 0.31; 0.84) relative risk of experiencing a new deformity, while women taking 2 g SR/day had a relative risk of 0.56 (95% CI 0.35; 0.89). The overall relative risk of a new deformity over the entire 2-year period, compared to placebo, was 0.71 (95% CI 0.49; 1.02) and 0.77 (95% CI 0.54; 1.09) in the SR 0.5 g/d and SR 2.0 g/d groups, respectively. Urinary excretion of bone-resorption markers was decreased in all treatment groups, while alkaline phosphatase (an indicator of osteoblast activity) was increased. Although the fracture risk was greater in the higher treatment group (2 g SR /d) versus the lower (0.5 g SR/day), the higher SR group experienced the greatest increases in BMD, about 3% per year. Adverse effects were mild to moderate, and the treatment was well tolerated in all treatment groups.

A second study evaluated the reduction in fracture risk in a phase III, randomized, double-blind, 3-year clinical trial utilizing 2 g SR/d or placebo in 1442 postmenopausal women (mean age approximately 69 years) with osteoporosis.4 All volunteers also received at lunchtime, dependent on dietary calcium intake, up to 1000 mg elemental calcium to ensure an intake of more than 1500 mg calcium daily, plus 400 to 800 IU vitamin D (form of vitamin D not specified), depending on their baseline vitamin D2 (25-hydroxyvitamin D) status.

After 12 months, total vertebral-fracture risk decreased by 49% in the SR group compared to placebo (P<.001), and the SR group also had a 52% reduction of symptomatic fractures (P=.003). By the end of the 3-year study, BMD in the SR group increased over baseline by 12.7% at the lumbar spine, 7.2% at the femoral neck, and 8.6% at the total hip (P<.001 for all three sites). Also by study end, volunteers taking SR had a 41% lower risk of a new vertebral fracture than those in the placebo group (P<.001). The researchers concluded that to prevent 1 patient from suffering a vertebral fracture, 9 patients would need to be treated for 3 years with SR.

A cautionary note should be inserted about SR. Strontium has an atomic mass greater than calcium. As such it attenuates the X-rays from a DEXA scan to a greater extent than calcium.3 Unless the radiologist corrects for this, the DEXA scan will not provide an accurate measure of BMD.3 Additionally, the form of strontium used in clinical trials (strontium ranelate) is not available in the United States. The form available in dietary supplements in the US is strontium citrate. Although the strontium citrate form may be effective at improving BMD and decreasing fracture risk, clinical trials have not been performed on strontium citrate to demonstrate its safety and efficacy.

Learn more

Why Osteo-K clobbers the competition: click to view a chart comparing Osteo-K to other leading calcium supplements, such as Viactiv, Citracal, Bone-Up, Os-Cal and Caltrate.

You can also learn more by reading our complete list of bone health topics.