Strontium (Sr) is an alkaline earth metal that shares a close chemical resemblance to calcium (Ca), the primary mineral component of human bone. This similarity allows strontium ions to be absorbed and incorporated into the skeletal structure, which is a property that has been both studied for therapeutic use and identified as a source of concern. For a period, a pharmaceutical form of strontium was utilized as an osteoporosis treatment due to its perceived ability to improve bone health and reduce fracture risk. However, the element’s interaction with the human body carries significant risks, leading to questions about its true benefit and overall safety profile.
Strontium’s Mimicry of Calcium in Bone Tissue
Strontium’s placement directly below calcium in the periodic table is the fundamental reason for its interaction with bone tissue. Due to this chemical kinship, the body’s mineral-handling mechanisms struggle to differentiate between the two elements. Strontium ions are readily taken up by bone-building cells and substitute for calcium ions within the body’s primary mineral structure, hydroxyapatite.
This substitution is a dose-dependent process, meaning that higher concentrations of strontium lead to a greater degree of incorporation into the bone matrix. In healthy bone, hydroxyapatite forms organized, strong crystals, but the introduction of strontium alters this delicate balance. Because strontium ions are slightly larger than calcium ions, their integration physically disrupts the normal crystal lattice structure of the bone mineral.
The body’s natural process for building and maintaining bone is unable to fully exclude strontium when it is present in high amounts. As a result, the new bone mineral being formed contains a significant, though heterogeneous, concentration of the foreign element. This foundational change in the bone’s mineral composition is the starting point for the element’s detrimental effects on skeletal integrity. This chemical mimicry, while initially exploited for therapeutic purposes, compromises the very material that provides bone strength.
The Compromise of Bone Quality vs. Measured Density
One of the most misleading effects of strontium incorporation is its impact on diagnostic testing for bone health. Strontium has a higher atomic mass than calcium, which causes it to absorb X-rays more intensely during standard Dual-energy X-ray Absorptiometry (DEXA) scans. When strontium replaces calcium in the bone structure, the resulting bone tissue appears artificially denser on the scan.
This phenomenon leads to an overestimation of the true bone mineral density (BMD), masking the actual mechanical properties of the bone. While DEXA scan results may show a positive increase in BMD, which is typically interpreted as a sign of stronger bone, the underlying structural integrity is often compromised. The substitution of strontium for calcium leads to a new mineral phase that is less stable and more brittle than pure hydroxyapatite.
The resulting bone, despite its higher measured density, is less mechanically sound and therefore potentially more fragile. This artificial density increase creates a false sense of security, as the patient may appear to have improved bone health on paper while having a bone matrix with reduced resilience. This compromised quality increases the potential for fragility fractures over time, undermining the entire purpose of the treatment.
Systemic Health Risks and Safety Warnings
Beyond the skeletal concerns, high levels of strontium exposure, particularly from the pharmaceutical product Strontium Ranelate, have been linked to serious systemic health risks. Major regulatory bodies, such as the European Medicines Agency (EMA), have issued severe restrictions due to these non-skeletal adverse effects.
One of the primary concerns is an increased risk of venous thromboembolism (VTE), which involves the formation of blood clots in the veins, leading to conditions like deep vein thrombosis or pulmonary embolism. Furthermore, clinical data demonstrated an elevated risk of cardiovascular events, including myocardial infarction, in patients taking the pharmaceutical form of strontium. This led to the product being contraindicated in patients with a history of cardiovascular disease or uncontrolled hypertension.
The drug’s safety profile also includes the risk of severe cutaneous adverse reactions (SCARs), such as Drug Rash with Eosinophilia and Systemic Symptoms (DRESS syndrome). DRESS syndrome is a rare but potentially fatal multi-organ hypersensitivity reaction that can manifest with fever, rash, and internal organ involvement. These serious risks ultimately led to the withdrawal or highly restricted use of Strontium Ranelate in many markets.
Sources of Harmful Strontium Exposure
The public may encounter strontium in a few different forms, ranging from highly regulated medication to unregulated dietary supplements. The prescription drug, Strontium Ranelate, was the focus of the serious safety warnings and is now heavily restricted or unavailable in most regions due to the systemic risks. This form was chemically engineered to enhance absorption and deliver a high, consistent dose of strontium.
In contrast, over-the-counter products, typically Strontium Citrate, are sold as dietary supplements to improve bone density. These supplements are not subject to the same rigorous testing and regulatory oversight as the pharmaceutical form. While the citrate form is often promoted as a safer alternative, it still introduces strontium ions into the body, which can be incorporated into the bone matrix and lead to the deceptive BMD overestimation.
Environmental exposure to strontium is generally low, but higher levels can occur in contaminated water or soil in specific geographic areas. Regardless of the source, the fundamental risk remains the same: the introduction of strontium ions into the body leads to their incorporation into the bone structure. For the average consumer, the use of unregulated supplements presents an unknown risk due to the lack of human efficacy and safety data, combined with the certainty of bone incorporation and potential BMD misrepresentation.