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Vitamin D and muscle injuries

July 15th, 2011

I’m on the record as a bit of a vitamin D skeptic. Not a total skeptic, mind you — it’s actually the only supplement of any kind that I take on a regular basis these days. But the claims that vitamin D enhances athletic performance have seemed pretty weak to me so far. However, I’ll dutifully pass along this press release from the American Orthopaedic Society for Sports Medicine, which describes some new research linking vitamin D levels with muscle injuries in NFL football players.

The study: 89 players from one NFL team were tested for vitamin D levels in spring 2010, during pre-season. Not surprisingly, the levels were generally low compared to what’s considered desirable (which seems to be true for pretty much every population group in the developed world):

Twenty-seven players had deficient levels (< 20 ng/ML) and an additional 45 had levels consistent with insufficiency (20-31.9 ng/mL). Seventeen players had values within normal limits (>32 ng/mL).

The team then provided data on time missed due to injuries during the season. Sure enough, players who suffered muscle injuries has “significantly lower levels” of vitamin D. How much lower? It’s not clear: this is conference data, so not yet published in a journal, and unfortunately the press release release doesn’t do a very good job of presenting the data. The average level for players with a muscle injury was 19.9, but it doesn’t tell us what the average for uninjured players was.

First thing to wonder: is it this cause or correlation? Do the players with crappy diets also neglect their strength, flexbility and warm-up routine? Second thing: if it is causal, what’s the mechanism? Why does this work?

Leaving that aside, I’ll just reiterate my hair-splitting distinction between a “performance-enhancing” substance and one that hurts performance if you’re deficient in it. Water helps your performance if you’re dehydrated, but we don’t consider it an ergogenic aid. As far as I can tell, vitamin D falls into the same category: something that you shouldn’t be deficient in, whether you’re an athlete or not. But I’m still not convinced that more is better if you’re in a healthy range.

  1. Audrey Giles
    July 15th, 2011 at 17:08 | #1

    Well said, as usual.

  2. July 16th, 2011 at 02:47 | #2

    The biggest gain from the use of vitamin D is by those who exercise less than 2 hours per day.
    Athletes are helped by vitamin D by:
    - Faster reaction time
    - Far fewer colds/flues during the winter
    - Less sore/tired after a workout
    - Fewer micro-cracks and broken bones
    - Bones which do break heal much more quickly
    - Increased VO2 and exercise endurance
    For details see Overview of Sport and Vitamin D @
    http://www.vitamindwiki.com/tiki-index.php?page_id=1259

  3. alex
    July 16th, 2011 at 09:57 | #3

    @Audrey: Thanks! :)

    @Henry: Thanks for the link. That being said, those athletic claims (e.g. increased VO2, endurance, reaction time, etc.) are precisely the ones that I’m not convinced are backed by anything resembling good science — though I’d certainly be happy to hear about it if there are good controlled studies out there that I’ve missed.

  4. July 24th, 2011 at 18:05 | #4

    as a former vit D researcher, just some notes: ‘healthy vit D status’ is not clear at the moment. In general USA studies refer to higher ‘healthy’ reference status than EU studies. It makes a difference is you compare vit D status with PTH or eg complaints of muscle pain.

    A problem with lots of Vit studies (but I think that is a problem with most studies in which nutrition is included) is that it is such a detail and very difficult to study in a praktical daily life setting. Who is eating every week precisely the same? And the same combination, so nutrition itself is already not interferring in the study?

    However I personly believe in the risk that topathletes who are doing indoorsports have a great risk for too low levels.
    At the other hand there are lots of claims about vit D which are not based on good studies.

    But interesting again!

  5. alex
    July 25th, 2011 at 00:54 | #5

    Thanks for the insights and context, @Kes — much appreciated. It certainly makes sense that top athletes in indoor sports have a high risk of low vitamin D levels. But do you think their risk of “deficiency” is any greater than an average non-athlete working in an office all day?

  6. July 25th, 2011 at 10:51 | #6

    Hi Alex,

    Good question. The status will be much depending on what people do during the weekends. If office-workers are outside a lot (with shorts, tops, no use of sunscreen) their levels can be quite okey. As long as it is not measured in early spring off course.During the sommar levels go up a lot, and for that you don’t have to be in the sun 7 days a week.
    At the other hand, in studies AND commercials the office-workers are often mentioned as possible riskgroups.

    I know from conversations (so no published reference) that nowadays the levels are tested in Gymnastics, because levels in injured girls were often low. I don’t know if the levels were lower in injured girls compared with non-injured girls, because then (5 years back) the levels were mainly tested in injured girls. I have been talking with the badminton federation about indoor-outdoor trainings and competions during weekends. There I suspect a low status, cause the athletes were mostly sleeping during the break between trainings and had very low amount of outdoor hours during daytime. Again, this is based on conversations. Future (top)atletes who are combining school and sports, are in general also less hours outside compared with regular teenagers. But again, this is based on conversations.

    The vit D receptor is in all types of cells, therefor is seems vit D has such a big influence on different outcomes. However the question is if we can use ‘it seems’ or ‘it has’.

  1. July 18th, 2011 at 21:55 | #1