Saturday, 31 August 2013

Calcium for healthy bones?

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”

Fracture healing
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.

Fracture prevention
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.

The guidelines
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.

6 comments:

  1. Makes good sense although as someone with surgically induced hypoparathyroidism, I wonder if that 1-2.5g daily limit of calcium applies to me? As I understand it, i have no means of controlling calcium uptake.

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    1. Yes, you come under the heading of "some other reason". Anybody with a deficiency in anything, whether it be magnesium or thyroid hormone, may require supplements. My point is that if you do not have a deficiency (malabsorption, overexcretion or dietary deficiency) you will not necessarily benefit from taking more.

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  2. I am puzzled that you would write on this subject with no mention of Vitamin K2. Even if Vitamin K2 has not made it yet to official recommendations, aren't you even curious about it? It only takes a few days of supplementation with MK-4 to see positive changes in the teeth--doesn't that suggest positive changes in the bones?

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    1. Thanks Jim,

      The reason I didn't cover vitamin K2 is because this blog post was on calcium and vitamin D, and I wanted to address the problem of overtreatment.

      As far as the evidence for vitamin K2 on bone strength, there is some evidence that it increases bone density (just as vitamin D does), but there is also evidence that it does not (http://www.ncbi.nlm.nih.gov/pubmed/19937427).

      Lots of things suggest other things. When you think something should work, like when you say "... positive changes in the teeth - doesn't that suggest positive changes in the bones?" - that is how we generate hypotheses. The next step is to test them. Vitamin D and calcium sound logical, but when put to the test, they don't reduce the fracture rate. And there is no evidence that vitamin K2 does either.

      Remember, it is clinical improvement we are trying to achieve (less fractures) not the surrogate (increased bone density). And no, one does not necessarily follow from the other, for reasons given in the blog. Treating numbers is easy (see the normalisation heuristic: http://doctorskeptic.blogspot.com.au/2012/10/treating-numbers-not-patient.html) - making patients better is hard, and many 'logical' treatments fail in this regard.

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  3. Please can you advise on the following : what is a normal diet ? ; can you be more precise than " a bit of sunlight " ? and what do you regard as a normal vitamin D level ?

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    1. All good questions. A normal diet in this context means that the diet has enough calcium in it in the first place, so that you don't need supplements. The average person needs to ingest between 1 and 1.5g of calcium per day. This is easy if you eat meat and dairy products and usually only becomes a problem if you don't.
      A bit of sunlight depends on your skin type, the latitude and the season, but you can read about it here: http://www.dummies.com/how-to/content/how-much-sun-do-you-need-to-make-vitamin-d.html
      Vitamin D levels are determined by blood tests, where a normal range is provided, although there is some argument about the exact cut-off.
      But if you don't want to worry too much about it, just go outside for half an hour per day with your face and hands exposed (less if it is hot and you have fair skin) and eat dairy products.

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