Years ago, in the first edition of my book, Better Bones, Better Body, I noted that high calcium intakes did not seem to prevent fractures. Cross-cultural data, in fact, suggested that countries with the highest calcium intake actually had the highest rates of osteoporotic hip fractures. Recently, sophisticated meta-analysis of the major published studies on the topic confirm my early breakthrough observation—and go beyond it to suggest possible risks of high, imbalanced calcium intakes. High calcium intakes do not prevent fractures, and may actually increase risk of hip fracture among some.
In my blog post, “Vitamin D is more important than calcium” I report on the US NHANES 111 survey finding that only for women with very low vitamin D levels is a higher calcium intake associated with better bone density. The large national survey (Bischoff-Ferrari et al. 2009) found that if women were not deficient in vitamin D (that is they had a vitamin D level above 20 ng/mL), a calcium intake higher than 566 mg per day was not associated with any greater bone density than with an intake of 566 mg calcium per day.
I doubt this lack of association between bone density and higher calcium intake among all but the vitamin D deficient came as a surprise to Bischoff-Ferrari and colleagues.
And why do I say these researchers were likely not surprised?
Because these scientists had already carefully analyzed all the studies on calcium intake and fracture risk.
• In 2005, Bischoff-Ferrari et al. conducted an overview analysis of studies on vitamin D and fracture prevention and concluded, ‘Thus, additional calcium supplementation may not be critical for non-vertebral fracture prevention once 700-800 IU of vitamin D are provided.” (Bischoff-Ferrari et al. 2005)
• Then again in 2007, the same group conducted a monumental meta-analysis of all major studies looking at calcium intake and risk of hip fracture. As they reported, “Pooled results from prospective cohort studies suggest that calcium intake is not significantly associated with hip fracture risk in women or men. Pooled results from randomized controlled trials show no reduction in hip fracture risk with calcium supplementation and an increased risk is possible. For any nonvertebral fractures, there was a neutral effect in the randomized trials.” (Bischoff-Ferrari et al. 2007)
And what about the possible increased risk of fracture they suggest?
In their meta-analysis they found four clinical trials which reported separate results for hip fracture. These clinical trials involving 6,504 subjects found a 64% greater risk of hip fractures with calcium supplementation. While this question of if, and how, high calcium intake could actually increase hip fracture risk is both complicated and speculative, a logical explanation the researchers mention is that “calcium alone may not prevent hip fractures in women” and that other nutrients are essential for bone strength. The other nutrients they mention include vitamin D, protein, and phosphorus — at least one of which (phosphorus) can be detrimentally impacted by high calcium intakes health.
All this new research supports our long-standing Better Bones position that at least 20 nutrients are key to bone health and that all these nutrients should help keep one nutrient in balance with the others.
Bischoff-Ferrari, HA, et al. 2005. Fracture prevention with vitamin D supplementation: A meta-analysis of randomized controlled trials. JAMA, 293(18): 2257-2264.
Bischoff-Ferrari, HA, et al. 2007. Calcium intake and hip fracture risk in men and women: A meta-analysis of prospective cohort studies and randomized controlled trials. Am J Clin Nutr, 86:17980-90.
Bischoff-Ferrari, HA, et al. 2009. Dietary calcium and serum 25-hydroxyvitamin D status in relation to BMD among U.S. adults. J of Bone Miner Res, 24(5):935-942.