6,000IU/Day of Vitamin D3 "Could" Trigger Improvements in Aerobic Metabolism & Performance in Professional Rowers

The study at hand was conducted with liquid vitamin D. Sincecaps and pills increase OHD levels effectively, it's yet unlikely that this explains the differences to other less successfull trials.

Zbigniew Jastrzebski from the Gdansk University of Physical Education and Sport found in his latest study that the provision of 6,000IU vitamin D3 per day did not just increase the levels of vitamin D3 in the blood of 14 elite light weight rowers by 400%, but "could be the reason for the improvement of aerobic metabolism in the rowers and reduction of their inflammatory reactions in response to the high-intensity training" (Jastrzebski. 2014).

I know that sounds kind of awkward without knowing what exactly the Polish scientists did. This is why I am going to give you a few more details below.
The experiment started on Mondays’ morning. The participants’ blood was taken from the cubital vein. Blood cell count, ASPAT, ALAT, GGTP, LDH, CK, total cholesterol, lipid profile (HDL, TGL, LDL), creatinine, phosphates, calcium salts, electrolytes (natrium, potassium, chloride) and the vitamin 25OHD (=vitamin D) content in blood were determined. In addition the scientists determined the total antioxidative status and the levels of lactic acid, the heart rate (HR), O2 uptake and kinetics as well as the respiratory exchange ratio (RER) in all subjects before and after 12 week supplementation with 6,000IU of liquid vitamin D3 (Vigantol) or identical placebo drops during and after a standardized graded exercise test on a Concept II rowing ergometer.

The same was true for most of the effects of the exercise regimen, which lead to significant increase in liver enzymes AspAT (asparagine aminotransferase), GGTP (gamma-glutamyltransferase) and LDH (lactate dehydrogenase) which suggest that the applied training program, after its completion, improved the function of some organs such as liver, heart or kidneys - with slightly greater increases in enzymes activity in the vitamin D group.

Figure 1: The vitamin D supplement added to the seasonal increase in vitamin D levels and increase the total antioxidant capacity of the rowers (Jastrzebski. 2014).

Significant increases in vitamin D were observed in both groups. In the non-supplemented group due to seasonal variation in the vitamin D group due to season variation and supplementation, which kicked the levels up to 120ng/ml which is more than 2x higher than "normal" (no, in the study at hand there were no side effects). Only in the former the scientists observed a corresponding, albeit non-significant increase in total antioxidant capacity, though.

In some, but not all subjects these changes went hand in hand with higher results of power and oxygen consumption obtained during a continuous graded exercise test in the vitamin D group. At the same time their blood parameters such as IL-1b, CRP, LDH reached lower values. As the author points out, "[t]he results suggest that vitamin D3, whose concentration in blood increased by 400% in GS as a result of supplementation, could be the reason for the improvement of aerobic metabolism in the rowers and reduction of their inflammatory reactions in response to the high-intensity training" (Jastrzebski. 2014) - a result that is quite surprising given the fact that the athletes were, unlike the subjects in previous studies with beneficial results, not vitamin D deficient at the onset of the study.
References:

• Dubnov-Raz, G., et al. "Vitamin D Supplementation and Physical Performance in Adolescent Swimmers." International journal of sport nutrition and exercise metabolism (2014).
• Jastrzębski, Zbigniew. "Effect Of Vitamin D Supplementation On The Level Of Physical Fitness And Blood Parameters Of Rowers During The 8-Week High Intensity Training." Analele Universităţii din Oradea Facicula Educaţie Fizică şi Sport 2 (2014): 57 - 67