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.

KEYWORDS:

• Military training
• hand grip
• vitamin D
• supplementation

Acknowledgments

The authors thank the conscripts who participated in the study as well as the command staff of the Kuperjanov Single Infantry Battalion for allowing access to the conscripts, sergeant major Terje Rammo for excellent technical assistance, and Ninni Sernert for critical review and statistical analyses.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors` contributions

Leho Rips – Designed research, analyzed data, writing of paper

Alar Toom – Analyzed data, writing of paper

Rein Kuik – Designed research

Ahti Varblane – Designed reserch, conducted research

Hanno Mölder – Conducted research

Helena Gapeyeva – Designed research, conducted research

Mart Kull – Analyzed data, writing of paper

Vahur Ööpik – Designed research

Jüri-Toomas Kartus – Primary responsibility for final content, writing of paper, and statistical analyses.

Helena Gapeyeva – Designed research, conducted research

Madis Rahu – Primary responsibility for final content, writing of paper

Data availability statement

The data sets generated and/or analyzed during the current study are available in the datadoi.ee University of Tartu Library repository, https://datadoi.ee/handle/33/342, http://dx.doi.org/10.23673/re-284

Ethics approval and consent to participate

The study was approved by the Research Ethics Committee of the University of Tartu No. 262/T-28 and 264M-14.

Additional information

Funding

This study was supported by the Estonian Defense Forces, funding agreement No. 0.4-2.5/16/1321.