Monday, July 8, 2013

Vitamin D for Athletes: 20,000 & 40,000IU / Week Bring Low Levels Back Up, Yet W/Out Measurable Performance Effect

Jumpstart low vitamin D-levels with 2,000 - 3,000 IU/day - but don't expect that to jumpstart your performance...
Most of you will probably remember the vitamin D news from the Short News on Saturday. And yes, I have to admit that as of now - the usefulness of known that both genetic polymorphisms and your vitamin D binding protein levels (which are incidentally higher in obese than lean individuals), are not exactly useful, when it comes to pick an appropriate dosage of supplemental vitamin D to bring your levels up into upper region of the normal range.

In this respect, a study like the one that has been published in the latest issue of the British Journal of Sports Medicine may in fact be more useful. After all, the study was designed to investigate two doses of vitamin D supplementation (20,000 vs 40,000 IU/week vs placebo) on serum 25[OH]D concentration in club-level male athletes over 6 and 12 weeks.
Note: If you read the Short News Update from Saturday, you will be aware that due to certain genetic polymorphisms you can be "vitamin D3 non-responder" (in the study by Nimitphong 40% of the subjects would could be considered low/no-responders due to the small scale of the study (N=20) this is yet not representative and may also be subject to inter-ethnic differences between Asians vs. Caucasians; learn more), if that's the case you may need 10,000-20,000IU à day or more - another reason to TEST not to supplement blindly!
Boring? Well, what if I tell you that the second aim of the study was to elucidate whether this protocol or rather the respective changes in vitamin D levels would have effects on the physical performance of the 30 21-year old athletes who were all competing for university athletics clubs (mostly rugby and soccer) in the UK (=low sun exposure)? ...I see, now you're listening. 

The research design was actually pretty straight forward: (0) Make sure none of your subjects has been popping vitamin D supplements of fish oil in the past; (1) Test the baseline performance and vitamin D levels of your study participants; (2) assign them via block randomization (to ensure there are no sign. inter-group differences in the baseline 25OHD levels) to three groups; (3) make them swallow either 20,000 or 40,000 IU vitamin D3 (cholecalciferol) or a visually identical placebo (PLB) (100 mg maltodextrin) once a week for 12 weeks; and (4) retest physical performance and vitamin D levels after 12 weeks.
Figure 1: The non-existent effects of vitamin D supplementation on the physical performance; neither the increments nor the decrements reached statistical significance (Close. 2013)
The study outcomes, at least as far as the performance increases are concerned could hardly be more unambigous. Despite the fact that 7/30 individuals (57%) had concentrations less than 50 nmol/l (=inadquate according to the US Institute of Medicine standards from 2011) and 6/30 (20%) were downright deficient (12-30 nmol/L) or severely deficient (<12 nmol/L) and irrespective of the fact that the subjects with the lowest D3 levels saw the most rapid increases in 25OHD levels, the research did not observe any significant improvements in the standardized performance tests. They do yet point out that
"[t]o further ascertain whether vitamin D status does affect skeletal muscle function in young
healthy participants, it may now be pertinent to also adopt more sensitive measurement techniques (eg, single muscle fibre measurements)." (Close. 2013)
Although I'll leave it up to you whether you want to ascribe a higher value to the corresponding gene essays that would be used in such an "advanced" study or the real world performance gains, I personally am not really interested in this kind of follow up study. It would make more sense to assign the subjects (preferable athletes and not yet another bunch of sick people, or even rodents) to a standardized exercise regimen and re-test, whether or not there would be any benefits of vitamin D supplementation in a more controlled training scenario.

Now that we've left the disappointing part behind, let's briefly take a closer look at the changes in v25OHD levels in figure 2. You will also realize that the higher dosage protocol produced a steeper incline in vitamin D levels, but was likewise unable to raise the vitamin D levels to the >120 nmol/ml range, where Heaney and other researchers would like to see it.
Figure 2: 25OHD levels in nmol/ml after 3 weeks and 6 weeks of supplementation (left), regression analysis demonstrating the dependence of serum total 25[OH]D increases on baseline levels (Close. 2013).
What's more, the way in which both supplementation regimen approach the 90-100 nmol/ml mark after 12 weeks of continuous supplementation suggests that it is probably not even feasible to bump your vitamin D levels into that region without taking even higher amounts of vitamin D on a daily basis to abrogate the natural regulation process which does not appear to favor "vitamin D council levels" in the >120 nmol/ml range. Even the Maasai and Hadzabe who live, as Luxwolda et al. put it in the "cradle of makind" have vitamin D levels that are approaching, but not surpassing the magic 120 nmol/ml margin (Luxwolda. 2012).

To get your levels in the recommended >75 nmol/ml range it should yet suffice to take ~2,000-3,000IU per day - or, for those with really low levels who are in a hurry to get them up into the normal range twice the amount.

Table 1: Prevalence of low(ish) vitamin D levels in athletes (based on overview in Close. 2013)
Talking about really low levels: I have not changed my mind about the importance of getting your vitamin D levels tested before you embark on a supplementation regimen with anything more than ~1,000IU/day. And if you take a second look at the dose-response relationship in figure 2, you will notice that you would only be wasting money if you took vitamin D supplements, when your levels are already in the optimal range.

Considering the fact that previous studies have revealed surprisingly high levels of vitamin D deficiency in athletes (see table 1), the money a bi-annual test may cost you is yet certainly well-spent. If not in terms of immediate performance increases then certainly with respect to your overall health. After all, contrary to the questionable benefits of brining your vitamin D levels into the >120 nmol/ml range, the evidence for (long-term?) detrimental effects of vitamin D deficiency is unambigous.

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