Strontium Citrate

Strontium is an alkaline earth element present in grains and seafood (range 0.3- 5.0 mg/kg) and is similar to calcium in terms of absorption and incorporation into bone. 25-30% of strontium in the diet is absorbed through the gastrointestinal tract and 99.1% of this is distributed in the mineralized tissue. The whole-body strontium content of an average (70kg) human is estimated at 320 mg (approximately 0.0005%by weight). Over-the-counter supplements containing strontium citrate are available in the US, which are being widely self-administered by patients to improve bone density.

In research on the effect of strontium citrate on bone consolidation during mandibular distraction osteogenesis, it was documented that strontium citrate improved the formation of new bone in the current rabbit model of mandibular distraction osteogenesis. The prolonged consolidation period may be shortened with strontium citrate, which may also have the potential to reduce complications.

There are no human studies evaluating the change in bone mineral density with strontium citrate. Much of the bone density increase being seen with strontium citrate is likely due to the replacement of calcium with strontium in the bone. Strontium has a larger atomic weight than calcium (38 vs 20), which causes it to attenuate X-rays more strongly than calcium. Comparisons of Ca hydroxyapatite (natural bone crystal) and Sr hydroxyapatite (Sr-substituted bone crystal) have revealed that for every 1% of strontium incorporated into the bone crystal, bone mineral density is overestimated by 10%. strontium citrate and strontium ranelate are both vectors for Sr delivery. In a study comparing the effect of the administration of strontium citrate and strontium ranelate, utilizing an in vivo X-ray fluorescence spectroscopy (XRF) system to quantify bone strontium accumulation in female rats, it was found that at 8 weeks, both strontium citrate and strontium ranelate were found to be equally efficacious at delivering Sr to bone. Another researcher used the same technique (XRF) to measure Sr levels in an osteoporotic subject self-administering strontium citrate at 680mg/day. After 2 ½ years, Sr levels were shown to be 7 to 15 times greater than at baseline. Higher concentrations were seen in the ankle, and with the incorporation of Sr in trabecular bone. Ankle Sr levels also did not seem to plateau within 2-3 years and continued to increase on supplementation.