Healthy Subjects, Trained Clinical Trial
Official title:
Effects of 12 Weeks of Vitamin D Supplementation on Muscle Characteristics in Trained Subjects
This study evaluates the effect of vitamin D supplementation on outcomes muscle performance and characteristics in 70 trained healthy individuals (18-40 years of age). Subjects will be allocated to ingest either vitamin D (35) or placebo (35) in a double-blinded fashion
Vitamin D insufficiency compromises muscle functionality, leading to changes in muscle mass
and strength, manifested at the cellular level. While this is increasingly recognized as a
problem for individuals with vitamin D deficiency (typically 25(OH)D < 25 nmol/l), there is
no general consensus for the remainder of the vitamin D-spectra. This lack of knowledge is
probably linked to the variation in protocols of studies that have investigated the
physiological role of vitamin D. These variations vary from aspects such as interventional vs
observational studies to aspects related to subject characteristics such as age, health and
training status. In this project, we will evaluate the effects of 12 weeks of vitamin D
supplementation (2000 IU/day) on muscle performance and characteristics in 70 trained healthy
individuals (18-40 years of age). Subjects will be allocated to either a vitamin D (35) or a
placebo group (35) in a double-blinded manner. They will be instructed to continue their
ordinary modes and frequency of training.
We anticipate baseline vitamin D levels in blood (and hence changes in vitamin D obtained
through supplementation), measured as 25(OH)D, to be a major determinant of the efficacy of
the intervention. This means that we expect individuals with low baseline levels of 25(OH)D
to display more pronounced changes in functional and biological outcome measures than those
with high baseline values. Such a scenario could be related to an inability of our protocol
to increase blood levels of 25(OH)D in individuals with higher physiological levels of
vitamin D (which essentially means that ingestion of vitamin D3 is leveled out or exceeded by
elimination of vitamin D derivatives). Alternatively, it may be related to inabilities of
tissues to respond to the resulting elevation in vitamin D levels. To study the individual
variation in vitamin D responses, data on both functional and biological variables will be
divided into quartiles based on baseline 25(OH)D-levels, whereupon comparisons will be made
between the low-end and high-end quartile. Individual variation will also be assessed using a
mixed model approach.
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