It’s one thing when my patients tell me that they are eating extra calcium to help their fractures heal or prevent new ones, but when my colleagues are advising them the same thing, its time to correct the bias. Taking calcium and/or vitamin D to heal fractures and prevent new fractures is another case of something that sounds good and is easy to believe, but doesn’t work as advertised.
Sounds like a no-brainer, right? After all, bones are made of calcium. Unfortunately, the usual combination of medical hubris, conclusion jumping, a desire to help, and some unintended consequences have turned this simple idea into a bad one. I am reminded of the quote from H.L. Mencken “For every complex problem, there is an answer that is clear, simple and wrong”
Humans need about 1g of calcium per day to make up for losses and keep the books balanced. The upper limit of this is about 2.5g. Calcium levels in the blood and the body are carefully regulated by a complex feedback and signalling mechanism involving many hormones (including vitamin D), the brain, the liver, the kidneys, the gut and the bones. Take too much calcium and you will pee it out, either as concentrated calcium or as kidney stones. It can also play up with you gastrointestinal system.
More to the point, there is no clinical evidence that supplementary calcium helps fracture healing, or prevents bones from not healing.
Most people are prescribed calcium and / or vitamin D to prevent future fractures, not for fracture healing. According to an extensive review of the scientific studies, vitamin D supplementation does not make a clear and consistent difference to the rate of falls, fractures or deaths. In high doses it can increase the measured bone density, but to what purpose if it doesn’t prevent fractures?
In another review, supplementary calcium was not associated with a clear or consistent reduction in mortality, or in the incidence of fractures, except in those whose diet was deficient.
And the findings were similar for calcium combined with vitamin D, except that the risk of fractures did decline in institutionalised elderly patients.
In all of the studies, the difference in the rate of fractures was not significant or small, despite increases in bone density and blood levels of vitamin D.
The harms from using supplementary vitamin D and/or calcium include gastro-intestinal symptoms, high blood levels of calcium, alteration of other calcium stabilising hormones, kidney stones, and heart attacks.
The lack of reduction in future fractures despite increases in bone density is because fractures are not strongly related to bone density. Fracture are more related to falling, and such things as eyesight, psychotropic drugs, age, medical comorbidities, balance, cognitive impairment and hazards in the environment. Again, we are going for the easy, obvious associations because they make sense and they are simple. Complex explanations are, by definition, harder work than simple ones.
Many guidelines, like this SIGN guideline, break patients down into many subgroups, and give all of them calcium +/- vitamin D.
However, the US Preventive Services Task Force have come out against decades of recommendations by stating that calcium and vitamin D supplements are not recommended for fracture prevention in non-institutionalised people.
The bottom line
If you have a normal diet, and get a bit of sunlight, and are not deficient in calcium or vitamin D for some other reason, then taking extra calcium and/or vitamin D will not significantly alter your fracture healing or your future risk of getting a fracture in the future. They might, however, cost you money, cause inconvenience and cause adverse effects.