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Vitamin D and Resistance Training

Vitamin D is one of the more absent nutrients in modern diets. It is synthesized in our body from sunlight in addition to being consumed from foods like meats, dairy, and fish. Its main purpose in the body is to help the absorption of calcium as well as cell growth. Low levels of Vitamin D in the body have been linked to increased risk of: diabetes (type II), cardiovascular disease, multiple forms of cancer, depression, osteoarthritis, and multiple sclerosis.
In the older population, Vitamin D deficiency is especially prevalent. These lower levels of Vitamin D cause Calcium absorption to decrease, which for an elderly person can have negative effects on bones and muscle size and strength. What if there was a way to increase muscle size and strength, even at an advanced age? A team of researchers out of Copenhagen, Denmark believed that there could be more to Vitamin D supplementation and resistance training. A preliminary study they conducted showed that Vitamin D supplementation can effect skeletal muscle, increasing the mRNA expression of an enzyme which turns Vitamin D from its inactive form into its active form, helping the absorption of Calcium into the muscle more efficiently.
The team of researchers designed a twelve week, double blind study to see how resistance training can effect skeletal muscle. Their hypotheses were that Vitamin D supplementation could: increase muscular hypertrophy and strength, increase diameter and number of type IIa muscle fibers, increase mRNA expression of VDR (Vitamin D receptor) on the muscle, and that the elderly would benefit more from supplementation as opposed to the younger population.
In this study, there were two groups of healthy, sedentary people. One group was a younger group, consisting of participants ranging from 20-30 years old. The other group was an older group, consisting of participants ranging from 60-75 years old. Within these two groups, there were two subgroups (four groups total). One group would be given a Vitamin D supplement (50 μg) as well as 800mg of Calcium. The other group would be a control group, only receiving 800mg of Calcium. The participants had 36 training sessions over a 12 week period (3 sessions per week), in which they performed knee extension and leg press exercises. A 5 Rep Max test (used in order to calculate a 1 Rep Max) was performed every 2 weeks to make sure the exercise protocol was progressing correctly.
The participants had 5 attributes measured before, during, and after the 12 week study. Cross Sectional Area (CSA), isometric muscle strength, serum Vitamin D levels, muscle fiber type, and mRNA VDR measurement. CSA and isometric muscle strength were also combined to show muscle quality.
After the 12 week study, some very interesting results were found. In regard to CSA and isometric muscle strength, all four groups saw increases. However, no significant increases were seen in any specific group. In terms of muscle quality (CSA combined with isometric muscle strength), the elderly Vitamin D group saw a larger increase compared to the younger Vitamin D group. For serum Vitamin D levels, blood tests from the participants showed both elderly and younger Vitamin D groups showed a higher concentration of Vitamin D as opposed to the placebo groups. With muscle fiber types, muscle biopsies from the participants’ Quadriceps (Vastus Lateralis) showed an increase in type IIa fibers and a decrease in type IIx fibers. Furthermore, the young Vitamin D group saw a significant increase in type IIa muscle fibers compared to their placebo group. In addition, the young Vitamin D group saw a significant decrease in mRNA expression of myostatin (causes atrophy in the muscle) compared to their placebo group. For mRNA expression of Vitamin D receptors on the muscle, no increases were seen across any of the groups.
What does the study mean for the rest of us? The young Vitamin D group saw increases in type IIa muscle fibers, which are also called fast twitch fibers. These kinds of muscle fibers are recruited more readily because they are easier to stimulate. Increases in fast twitch fibers mean your muscles will work faster. In addition, the decreases in myostatin allow for less atrophy in the muscle. As for the elderly, greater muscle quality is very important. Greater muscle quality can mean a healthier, less sedentary lifestyle, allowing for a longer life. With this comes greater absorption of Calcium, allowing for increased bone density, which is paramount in advanced age. The moral of the story is: get your Vitamin D in however you can.

Agergaard, J., Trøstrup, J., Uth, J., Iversen, J., Boesen, A., Andersen, J., . . . Langberg, H. (2015). Does vitamin-D intake during resistance training improve the skeletal muscle hypertrophic and strength response in young and elderly men? a randomized controlled trial.Nutrition & Metabolism Nutr Metab (Lond).

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