The Effect of Vitamin D Supplementation on Muscle Power in Elite Cyclist
Condition: Muscle Power
Study type: Interventional
Phase: Phase 4

Summary: 
      The purpose of this study is to evaluate the change in vitamin D status with the change in
      muscular strength and muscular power in highly trained athletes over a 9-month study period.
      The investigators hypothesize that the greatest muscular strength and power gains will be
      demonstrated in the athletes who achieve and maintain a 25(OH)-D > 50 ng/mL (but < 100 ng/mL)
      over the 6 month study duration.

      This hypothesis will be tested by carrying out the following specific aims: Aim 1. to
      determine the extent to which increasing serum 25(OH)D to > 50 ng/mL is associated with
      improved muscular power by assessing specific performance measures (e.g. Vertical Jump Test
      and Wingate test) relative to lean body mass; and Aim 2. to examine the correlation between
      vitamin D status and muscular power over time.
    

Detailed description: 
      Study will be advertised through flyers at the training facilities and by word of mouth.
      Researchers will schedule meeting with club members at the training facilities. At the
      meetings, the researchers will give an explanation of the study and address any concerns or
      questions that they may have. Cyclist will have an opportunity to sign up for participation
      on a sign-up sheet or e-mail the PI directly to minimize any chance of coercion. Meetings
      will take place in the training facilities in Tulsa, Oklahoma or the Oklahoma City
      Metropolitan Area. At this time, subjects will complete an informed consent along with
      demographic, anthropometric and health history, sunlight exposure, calcium and food frequency
      questionnaires and PAR Q. All subjects will be asked to fill out the questionnaires in the
      training facilities at various locations to ensure privacy. After completion of the
      appropriate questionnaires, cyclist will be have venous blood from the dominant arm (i.e., ~
      5 cc of blood) collected by a licensed medical professional and serum samples stored for
      future analysis of vitamin D metabolites (i.e., 25-OH-vitamin D and 1,25-OH-vitamin D) and
      parathyroid hormone (PTH) concentrations. The cyclist's arm will be cleaned with an alcohol
      swab, the blood will be drawn into a sterile vacutainer using a sterile needle. At the
      completion of blood collection, the arm will again be cleaned using sterile gauze and covered
      by a band aid to minimize the risk of infection. Samples will be placed on ice in an ice
      chest until they are processed in the Nutritional Sciences laboratories at Oklahoma State
      University. Subjects will then undergo skin tone analyses followed by evaluation of specific
      performance measures of muscular strength and power. These performance measures include:
      vertical jump test and a Wingate Power Test. All testing and blood collection will take place
      at the training facilities.

      Within 4 weeks of completing the baseline assessment, the investigators will meet with the
      cyclist at their training facilities. Participants will be randomly assigned to placebo or
      the vitamin D supplemented group. The vitamin D supplementation will consist of 100 mcg of
      vitamin D/d, to be taken throughout the day. Participants will achieve 100 mcg by taking 2 x
      25 mcg capsules per day. One will be taken at each time point (i.e., morning and evening)
      throughout the day. Currently, there is no evidence suggesting that athletes require more
      vitamin D then the general population for their age. Although we do not anticipate that the
      dose of vitamin D used in this study, will produce intoxication (150 ng/mL), subjects who
      exceed 100 ng/ml (i.e., upper end of the normal range) at any time will be asked to
      discontinue the study. Studies that have demonstrated the benefits of vitamin D
      supplementation on muscular strength and muscular power have combined vitamin D with calcium.
      Therefore, all subjects (placebo and vitamin D supplemented group) will be given a
      commercially available supplement of calcium and instructed to take with breakfast. The
      calcium supplement is in the form of calcium citrate (500 mg per capsule).
    

Intervention name(s): Vitamin D; Placebo
Intervention type(s): Dietary Supplement; Dietary Supplement
Intervention description(s): The vitamin D supplementation will consist of a capsule of 100 mcg of vitamin D/d, to be taken throughout the day. Participants will achieve 100 mcg by taking 2 x 25 mcg capsules per day. One will be taken at each time point (i.e., morning and evening) throughout the day. They will take the vitamin D supplement for the 6 month intervention period; Participants in the placebo group will receive a capsule containing the inactive ingredients that include cellulose and silica to create a gel-like substance
Other intervention name(s): Cholecalciferol
Intervention MeSH terms: Vitamin D; Cholecalciferol
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Triple (Participant, Investigator, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: Muscle Power; Vitamin D; Vitamins; Cholecalciferol