Thursday, January 26, 2012

What is Strontium?

Strontium is probably the most-heavily studied mineral treatment for osteoporosis that you’ve never heard of, unless you’re a naturopathic doctor or a geriatrician. In the discussion of osteoporosis prevention and treatment, we hear a lot about calcium, magnesium, vitamin D, and vitamin K, but rarely do we hear about strontium – most of us probably couldn’t even find it on a periodic table if we had to. Even so, strontium has a pretty extensive amount of research behind it, and has been shown to not only improve bone density (as measured on a DXA scan), but it has also been shown to help reduce the risk of fracture, which, when you’re dealing with osteoporosis, is the most important thing to see.

So to start with, what is strontium? Strontium is a trace mineral that occurs naturally in the diet, albeit in small amounts, typically about 1-3 mg/day. Typical sources of strontium are whole grains, leafy greens, and root vegetables, i.e. all the usual suspects. As a supplement, however, strontium is typically dosed at a much higher level, in a range of 450mg to 2g per day. Any time a nutrient is dosed at a level much higher than it would occur in the diet naturally, science studies it extensively, to verify that it’s both safe and effective, and strontium is no exception.

Some older articles seemed to suggest some safety issues about strontium, suggesting that strontium might contribute to bone growth disorders. In one case, young rats fed a high strontium diet developed bone mineralization defects, and in another, children living in a part of Turkey with high levels of strontium in the soil (and thus food) demonstrated higher-than-normal incidence of rickets. In both situations, however, the bone disorders seem to have been related to the respective diets’ relatively low levels of calcium. Since then, multiple studies have confirmed that patients taking high doses of strontium, who are eating otherwise balanced diets or taking supplemental calcium, do not develop bone disorders. Indeed, patients taking high levels of strontium for the prevention or treatment of osteoporosis have normal bone structure.

So what about it’s efficacy? In the early 2000’s, two major studies were undertaken to assess whether strontium renalate (a prescription form of strontium used in several European research studies) was an effective treatment for osteoporosis, including its ability to increase bone mineral density (as measured on a DXA scan) as well as its ability to reduce incidence of fractures. The Spinal Osteoporosis Therapeutic Intervention (SOTI) trial and the Treatment of Peripheral Osteoporosis (TROPOS) trials both found that strontium renalate increased bone mineral density and reduced fracture risk in postmenopausal women with osteoporosis, with some of the greatest treatment effect noted in women over 80 years of age (1, 2, 3), who are at the greatest risk of fracture. Data from these studies and other sources prompted the Cochrane Review to award strontium renalate with silver level evidence in the prevention of vertebral and nonvertebral fractures, as well increasing bone mineral density. These two studies demonstrated positive results over relatively short periods of time (three and five years, respectively), and so questions remained about their long-term efficacy. This last year, however, an extension study of women involved in the SOTI and TROPOS studies indicated that strontium renalate continued to support increases in bone mineral density and a strong reduction in risk of fracture over a ten-year period with minimal side effects, thus establishing it’s safety and efficacy over long periods of time.

Sounds great right? Well, here’s the catch. Strontium renalate is not currently approved for use in the United States. The biochemist in me would believe that strontium should be active in forms other than this one – i.e. that strontium chelate, strontium citrate, and other would have similar activity. However, this being science, we need evidence, and unfortunately, there’s not a lot out there on other forms of strontium. I found one study stating that dietary strontium increased bone mineral density in an animal model, suggesting that other forms of strontium may have beneficial effects. On the other hand, I found another study which showed that strontium renalate was far more effective than strontium chloride at delivering strontium to the bone; while this doesn’t tell us for sure about strontium citrate, chelate, etc, it certainly suggests that strontium’s efficacy depends highly on the form it is delivered in.

So the take-home message is this: strontium renalate is effective in the treatment of osteoporosis, but other forms may not be. The paucity of evidence regarding other forms of strontium makes it very hard to make any statements about their effects, beyond speculation or educated guesses – I had my druthers, I’d be calling for research into strontium citrate, strontium chelate, and other forms. If you’re a health care consumer and have been diagnosed with osteoporosis or osteopenia, make sure you’re getting regular DXA scans – other forms of strontium may be effective, but the ultimate test is going to be your own bone density. Continue to follow the tried and true prevention methods, such as calcium and vitamin D supplementation, and engaging in weight-bearing exercise.