|Jumpstart low vitamin D-levels with 2,000 - 3,000 IU/day - but don't expect that to jumpstart your performance...|
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)|
"[t]o further ascertain whether vitamin D status does affect skeletal muscle function in youngAlthough 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.
healthy participants, it may now be pertinent to also adopt more sensitive measurement techniques (eg, single muscle ﬁbre measurements)." (Close. 2013)
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).|
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)|
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.
- Close GL, Russell J, Cobley JN, et al. Assessment of vitamin D concentration in professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function. J Sports Sci 2012.
- Bescos Garcia R, Rodriguez Guisado FA. Low levels of vitamin D in professional basketball players after wintertime: relationship with dietary intake of vitamin D an calcium. Nutr Hosp 2011. 26:945–51.
- Ducher G, Kukuljan S, Hill B, et al. Vitamin D status and musculoskeletal health in adolescent male ballet dancers a pilot study. J Dance Med Sci 2011.15:99–107.
- Halliday TM, Peterson NJ, Thomas JJ, et al. Vitamin D status relative to diet, lifestyle, injury, and illness in college athletes. Med Sci Sports Exerc 2011. 43:335–43.
- Hamilton B, Grantham J, Racinais S, et al. Vitamin D deﬁciency is endemic in Middle Eastern sportsmen. Public Health Nutr 2010. 13:1528–34.
- Heaney RP. Assessing vitamin D status. Curr Opin Clin Nutr Metab Care 2011;14:440–4.
- Lehtonen-Veromaa M, Mottonen T, Irjala K, et al. Vitamin D intake is low and hypovitaminosis D common in healthy 9- to 15-year-old Finnish girls. Eur J Clin Nutr 1999. 53:746–51.
- Lovell G. Vitamin D status of females in an elite gymnastics program. Clin J Sport Med 2008. 18:159–61.
- Luxwolda MF, Kuipers RS, Kema IP, Dijck-Brouwer DA, Muskiet FA. Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. Br J Nutr. 2012 Nov 14;108(9):1557-61.
- Morton JP, Iqbal Z, Drust B, et al. Seasonal variation in vitamin D status in professional soccer players of the English Premier League. Appl Physiol Nutr Metab 2012. 37:798–802.
- Wilson G, Fraser WD, Sharma A, et al. Markers of bone health, renal function, liver function, anthropometry and perception of mood: a comparison between Flat & National Hunt jockeys. Int J Sports Med 2012.