Lose fat, gain muscle, and get strong by making sure your vitamin D levels are up to par. Now is the time to pay attention to your vitamin D status since we are entering autumn in the Western hemisphere, and new research shows a direct relationship between vitamin D status and muscle strength in men and women of all ages.
The study, published in the journal Medicine and Science in Sports and Exercise, found that in healthy men and women aged 20 to 76, vitamin D status was significantly related to muscle strength. Interestingly, higher vitamin D status was associated with greater isometric and isokinetic strength in the arms, but only with isometric strength in the legs. Researchers think this is because vitamin D interacts with type II muscle fibers to a greater degree than type I fibers. There is generally a greater distribution of type II fibers in the biceps brachii than in the four quadriceps muscles tested in this study.
Previous evidence support the suggestion that vitamin D levels influence strength and muscle fiber size in the type II fibers to a greater degree than type I. For example, its been established that vitamin D deficiency affects type II fibers directly and can produce muscle dysfunction and atrophy when blood vitamin D levels drop below 30 ng/ml. In one study of elderly women with clinical vitamin D deficiency (levels below 15 ng/ml), type II muscle fiber atrophy of the gluteal muscles was much greater than in women who had adequate vitamin D.
A second study showed that giving 1,000 IUs of vitamin D to older women who were D deficient produced an average increase in type II muscle fiber growth in the vastus lateralis of 96.5 percent! This translated into a 59 percent decrease in falls. These results are fascinating because they indicate that a simple way to prevent muscle loss and improve mobility as we age is to ensure adequate vitamin D.
In addition, from a performance point of view, it highlights the need for people of all ages to get enough vitamin D in order to support muscle development and fat loss from training. You might think it’s a stretch to associate sufficient vitamin D levels with fat loss, but we know that vitamin D deficiency can lead to fat accumulation in the muscle in young, healthy women. Plus, studies show that people with higher vitamin D levels tend to have less belly fat and less total body fat.
Another possible reason for the stronger association between vitamin D levels with the arms rather than the legs has to do with the androgenic effect of vitamin D. A recent study showed that vitamin D supplementation of 3,332 IUs a day by middle-aged men increased free testosterone levels, which may then have a greater tissue-building effect on the upper over the lower body. Researchers are unclear how vitamin D increases testosterone, but think it may decrease the aromatization of testosterone to estrogen.
Take away a commitment to getting enough vitamin D and having your blood levels tested regularly throughout the winter months. This is a simple way to ensure you get the most out of your training. The effect of vitamin D in the body appears to be even greater than we previously thought since this new data shows it not only supports type II fiber strength and size, but it has a direct effect on healthy hormone levels.
Grimaldi, A., Parker, B., et al. Vitamin D Associated with Greater Muscle Strength in Healthy Men and Women. Medicine and Science in Sports and Exercise. 2012. Published Ahead of Print.