If people in their twenties start strength training they’ll lose more fat around their middle if they take vitamin D too. What’s more, they’ll build up more speed, write sports scientists at Purdue University in an article soon to be published in Clinical Nutrition. But the supplementation had no effect on increase in muscle mass or strength as a result of training.
If the basic research that’s been done is anything to go by, vitamin D supplementation should result in more muscle. Almost everyone living a modern way of life has less vitamin D in their blood than they should have, and vitamin D stimulates the development of muscle cells. But the results of human studies are variable.
If you give elderly people a daily 400 IE for nine months and get them to do weight training, then the supplement has hardly any effect on muscle mass and strength. [Exp Gerontol. 2006 Aug; 41(8): 746-52.] But if you give non-active elderly people 1000 IE vitamin D every day for two years, then the number and size of their fast type-2 muscle fibres increase. [Cerebrovasc Dis. 2005;20(3):187-92.]
So what’s the deal? Does vitamin D add something to strength training or not?
The researchers at Purdue University tried to work out the answer. They gave a dozen fat people in their twenties 4000 IE vitamin D and 500 mg calcium every day for 12 weeks, and they gave a similar group a placebo.
All subjects trained three times a week with weights and machines. They did three sets each of leg extensions, leg curls, leg press, hip adduction, hip adduction, chest press, seated row and pull downs with 70-80 percent of the weight with which they could still just manage 1 rep. After a workout they drank a liquid meal replacement containing 54 g carbohydrates and 20 g milk protein isolate.
For the seated row, the subjects in the supplementation group were able to raise the weights faster than the subjects in the placebo group. That meant they built up more power. In week four the difference between the two groups was statistically significant.
The higher the vitamin D level rose the greater the change in the waist/hip circumference ratio in the favourable direction, the researchers also discovered. This was mainly because the subjects in the vitamin D group lost more fat around their waist.
Nice results, but the researchers had expected more. They found no effect on the increase in muscle mass, on the increase in muscle power, total fat mass, maximal oxygen uptake or glucose uptake by the muscle cells.
The researchers suspect that supplementation, despite the dose being high by today’s standards, didn’t cause a sufficient rise in the vitamin D level. It rose by an average of 13 ng per ml. The researchers had expected a rise of 28 ng/ml. Perhaps 12 weeks is too short a time for effects to become visible, the researchers suggest.