Seven-month wintertime supplementation of 1200 IU vitamin D has no effect on hand grip strength in young, physically active males: A randomized, controlled study

Abstract

Background There has been a growing interest in the role of vitamin D for the well-being and physical performance of humans under heavy training such as conscripts in military service; however, there is a lack of long-term supplementation studies performed on members of this type of young, physically active, male population. The hypothesis of the study was that vitamin D supplementation during wintertime will decrease the prevalence of critically low vitamin D blood serum levels and increase hand grip strength during the winter season among young male conscripts. Study Design Longitudinal, triple-blinded, randomized, placebo-controlled trial. Methods Fifty-three male conscripts from the Estonian Army were randomized into two groups: 27 to an intervention group and 26 to a placebo group. The groups were comparable in terms of their demographics. The intervention group received 1200 IU (30 µg) capsules of vitamin D3, and the control group received placebo oil capsules once per day. The length of the follow-up was 7 months, from October 2016 until April 2017. Blood serum vitamin D (25(OH)D), parathyroid hormone (PTH), calcium (Ca), ionized calcium (Ca-i), testosterone and cortisol values, and hand grip strength were measured four times during the study period. Results The mean 25(OH)D level decreased significantly in the control group to a critically low level during the study, with the lowest mean value of 22 nmol/l found in March 2017. At that time point, 65% in the control group vs 15% in the intervention group had 25(OH)D values of less than 25 nmol/l (p < 0.001). In the intervention group, the levels of 25(OH)D did not change significantly during the study period. All other blood tests revealed no significant differences at any time point. The corresponding result was found for hand grip strength at all time points. Conclusion Long-term vitamin D supplementation during wintertime results in fewer conscripts in the Estonian Army with critically low serum vitamin D (25(OH)D) levels during the winter season. However, this did not influence their physical performance in the form of the hand grip strength test.

Effects of Probiotics and Vitamin D3 Supplementation on Sports Performance Markers in Male Mixed Martial Arts Athletes: A Randomized Trial

“…Thus, no spectacular changes in MMA athletes were observed. It was also shown that seven months of vitamin D 3 supplementation (1200 IU daily) had no effect on calcium, parathormone, cortisol, and testosterone blood concentrations, as well as hand grip strength among Estonian soldiers [ 49 ].…”

High dose vitamin D supplementation decreases the risk of deficiency in male conscripts, but has no effect on physical performance—A randomized study

“…The primary variable of the study was the level of 25(OH)D in the serum. Based on the findings in the study of Rips et al [ 36 ], a difference of 20 nmol/L between the study groups was considered meaningful to measure. For example, for an SD of 25 nmol/L, 26 participants would be needed in each group to reach a power of 80%.…”

“…In an Estonian‐population‐based study, Kull et al [ 21 ] found mean winter serum 25(OH)D levels of 43.7 nmol/L. In a randomized controlled study (RCT) by Rips et al [ 36 ], the lowest mean 25(OH)D value of 21.9 nmol/L was found in March in a placebo group of young men undergoing military service. Another Estonian study found critically low vitamin D values (<25 nmol/L) in 36% and deficiency (<50 nmol/L) in 92% of young conscripts in the spring season [ 35 ].…”

“…The same daily intake of 600 IU is suggested by the Nordic Nutrition Recommendations panel [ 23 ]. Rips et al [ 36 ] found that daily winter‐ and springtime supplementation with 1200 IU for seven months in young male conscripts resulted in a mean maximum 25(OH)D value of 59.8 nmol/L, which was slightly reduced during springtime and had a lowest mean value of 50.2 nmol/L in March. The Endocrine Society Committee suggests a daily supplementation between 1500 and 2000 IU for those in the population at risk of deficiency, and it suggests an upper limit of 4000 IU in young men [ 18 ].…”

“…Based on current evidence, supplementation with 1200 IU vitamin D is not enough to reach sufficient 25(OH)D levels in Estonian conscripts [ 36 ]. A prospective, randomized study, with two different supplementation dosages was designed, involving young male conscripts in the Estonian Army to examine the effect of vitamin D supplementation on muscular fitness and 25(OH)D blood serum levels.…”