A study published on Friday 5th October caused quite a stir. It was reported worldwide with headlines such as “Vitamin D Supplements Don't Help Bone Health, According To Huge Study.”
The study was indeed large. It was a meta-analysis (when lots of trials are grouped together – considered the best evidence possible) of 81 trials involving over 50,000 people. The study concluded that vitamin D supplements had no effect on total fracture, hip fracture or falls. The UK government advises intakes of 10mcg daily and recommends a daily supplement at this level in autumn and winter. The US government advises even higher intakes – 15mcg daily from the age of 1 to 70 and 20mcg daily over the age of 70.
I took a good look at the full paper (it’s not available on open view) and the lead author kindly sent me a copy of the appendix (more data than can be dreamed of!) My first reaction to the paper was surprise. Then I gave more thought to the 81 trials and what they had actually done and to which people and then I wasn’t surprised anymore.
I looked primarily at fractures – as that was the most robust outcome looked at in the study. (What does a fall that didn’t lead to a fracture tell us?) I came to the conclusion that there could be many reasons why the trials didn’t find that vitamin D supplementation led to differences in fractures. The five most obvious were:
1) The people in the trials may have had adequate vitamin D levels at baseline – in which case a supplement would make little difference.
2) The people in the trials may have been taking a supplement for too short a time – in which case a supplement would make little difference.
3) The people in the trials may have been taking too low a dose for the supplement – in which case a supplement would make little difference.
4) The people in the trials may not have been taking other nutrients that vitamin D works with – in which case a single supplement would make little difference.
5) There may be other risk factors for fractures and falls that outweigh any benefit that can be achieved with a vitamin D supplement.
I looked at each of these in turn, using evidence from the paper and the appendix. I also looked at bone health in general and risk factors for fractures. Who gets them and at what age? There were some really interesting findings.
My overall conclusion was that the right trials have not been done to be able to definitely state that vitamin D doesn’t help bone health. I also put the government advice to take a supplement in context with their other advice that impacts bone health: sunbathing advice, statin guidelines and dietary advice. My bottom line was – ignore government advice on everything or nothing. The full review below explains why.
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