December 8, 2009
Dear Editorial Staff,
As a physician and a doctor who practices an integrative approach to medicine that includes natural solutions, I feel compelled to write you this letter in response to the overwhelming amount of misinformation I’ve seen in advertisements promoting certain bone building nutrients. The growing number of bone health supplements containing strontium (Sr) presents a concern in that none of these products include adequate cautionary statements about this ingredient. While it is true that Sr is a naturally occurring element, no unique natural role for it has been identified for human metabolism. The levels being provided for supplementation (680 mg elemental) are several hundred times the amount which naturally occurs in the diet (2-4mg/day). (Nielsen (2009) Bone 35(3) 583-8). These pharmacological dosages have never been studied for use in a supplement. The only long-term usage of Sr has been as the drug strontium ranelate, which could be taken only under a doctor’s supervision. Long term safety studies of strontium ranelate (Cochrane Review, 2006) have revealed significant increases in the risk of serious vascular and nervous system disorders, as well as accumulation of strontium in patients with impaired kidney function. There is no reason to expect that strontium citrate (the supplement) will behave any differently, and the absence of any warnings on Sr supplement products (at the very least a contraindication for those with impaired kidney function) is disturbing.
Additionally, although Sr has been shown in a clinical setting to promote bone growth, it also artificially inflates bone mineral density (BMD) measurements because it is denser than the calcium it replaces. This can be problematic for consumers who are closely monitoring their bone density inasmuch as Sr causes DXA measurements to inaccurately report more bone mineral content than actually exists. A bone Sr content of 1% can overestimate BMD by as much as 10%. Even relatively short term (3-4 year) supplementation can increase bone Sr content to 0.6% (Blake et al. (2007) J Clin Densitom. 10(3):259-65). When Sr was given by prescription and monitored by a physician, this overestimation of BMD could be corrected, but because supplement usage typically isn’t monitored as closely by a physician, this overestimation in BMD may not be easily corrected. And because Sr is retained in bones better than calcium (one of its mechanisms of action), inaccurate BMD measurements can continue even after discontinuation of Sr usage. Six months after discontinuation of usage, bone Sr content could be upwards of 70% (Barenholdt et al (2009) 45(2) 200-6). Several studies have revealed elevated bone Sr content years after discontinuation of usage. One study estimates it could take upwards of 25 years to return to baseline bone Sr levels.
There has been successful clinical work on strontium ranelate, and its history as a drug has verified supplemental Sr as an alternative bone-building ingredient. However, it is the duty of responsible supplement manufacturers to make consumers aware of the potential drawbacks of supplemental strontium (serious potential side effects and contraindications, as well as diagnostic difficulties arising from its usage) so that consumers can make informed decisions concerning their well-being.
Yours in health,
Paz Eilat, MD