Table 2

Frequently asked questions about vitamin D supplementation

What type of vitamin D should the athlete take?
  • Cholecalciferol (D3) is preferable to ergocalciferol (D2).19

  • Vitamin D3 is more effective than D2 in achieving desired serum levels.131 137

Oral or intramuscular vitamin D supplementation?
  • Both routes are effective.138 139

  • Intramuscular route can lead to unpredictable release from injection site.

  • Serum levels rise quicker with oral administration but by 3/12 response is similar.140

  • Overall, oral supplementation is preferable in the athletic population unless there are any malabsorption issues.

Where should an athlete source vitamin D supplements?
  • Athletes subject to drug testing should only source supplements from manufacturers known to comply with antidoping agency testing regulations.

Should the athlete take a daily or intermittent dose of vitamin D?
  • Little difference in effectiveness for vitamin D taken daily or in larger, less frequent doses.140

How quickly will serum levels rise after starting supplementation?
  • Variable and dependent on a number of factors: initial serum levels, sun exposure, normal dietary intake, time of year, age, BMI, skin type, comorbidities and genetic profile.

  • ‘Rule of thumb’:

  • Healthy individuals: 1000 IU/day>serum levels rise by 25–30 nmol/L in 3–4 months.19 141

  • Severely deficient: may need doses in >1000 IU/day to achieve adequate levels.134

When should athletes be routinely screened?
  • No consensus.

  • If annual: same time of year preferable.

  • If biannual: end of winter and end of summer will give best indicator of absolute values and annual variability.

Where should values be assessed?
  • Considerable variability between different commercially available assays.142

  • Use same laboratory for repeat screening for continuity.

Vitamin D alone or with calcium (1200 mg)?
  • Combination appears to confer better bone protection.20–22