Vitamin D is essential for muscle function and normal muscle size, according to a new study that is carried out by scientists at Westmead Institute for Medical Research in Sidney. Lack of vitamin D may result in impaired muscle function, including such problems as poor physical fitness level, muscle tension and loss of muscle mass.
Vitamin D is viewed as a hormone that can activate and influence most cells and organ systems in the body. It is commonly known that vitamin D is important for bone health and the immune system, but there is growing evidence that the vitamin also plays a role in muscle function. One reason is that vitamin D is a determining factor for muscle cells and their ability to communicate with one another. This insight may turn out to be highly important for the many people suffering from various muscle diseases and sarcopenia (loss of muscle mass). Sarcopenia is particularly problematic for chronically ill people and seniors, as it affects their musculoskeletal function and impairs quality of life.
Loss of muscle mass and reduced strength
Most cells in the human body have vitamin D receptors, and vitamin D is believed to control around ten percent of our genes. The scientists from Westmead Institute for Medical Research in Sidney observed that mice with no vitamin D receptors in their muscle cells (myocytes) had smaller muscles, and their muscle strength was also reduced. For the same reason, these mice were unable to run as fast or far as mice that had vitamin D receptors in their muscle cells. According to Professor Jenny Gunton who lead the study, science has known for a long time that a vitamin D deficiency is associated with impaired muscle strength and increased risk of falls and fractures. However, little was known about how exactly the vitamin influenced muscle function.
The scientists revealed that normal muscles have comparatively few vitamin D receptors, but if you remove all vitamin D receptors in muscle cells (like they did in the study) it affects muscle function in a number of ways.
In other studies, Professor Gunton has successfully removed all vitamin D receptors in mice, something which, needless to say, has a wide range of implications. However, the results of the latest study point to some very important differences, as muscle cells lose their ability to communicate.
Vitamin D supplements – a new weapon in the treatment of muscle diseases
Professor Gunton and her team of scientists saw that mice without vitamin D receptors in their muscle cells had normal-sized bodies, but they had less muscle strength and more body fat. When these mice exercised in their treadmills, they ran at lower speed and for a shorter period of time. Of course, this in itself could be contributing to their lower muscle mass and larger amount of body fat. However, the mice also had substantially lower grip strength, starting very early in life. In humans, reduced grip strength is typically associated with ageing.
Professor Gunton calls for more research in this area. Still, the results of their study do suggest that the maintenance of vitamin D signaling in muscle cells is important for preserving muscle mass and muscle cell function throughout life. In fact, this study may even open a new door in terms of therapies targeted at muscles and their need for vitamin D.
These therapies may help treat or prevent various ailments that are associated with impaired muscle function – including age-related sarcopenia, which is a degenerative loss of muscle mass.
The research article is published in Journal of Cachexia, Sarcopenia and Muscle
Many people – especially seniors – fail to get enough vitamin D
The major source of vitamin D is the sun during the summer period, but because of factors such as too little outdoor activity, lack of sunshine during the winter, overweight, and ageing processes, many people lack vitamin D.
Reference intake levels for vitamin D vary from country to country. In Denmark, the reference intake (RI) for adults in general is five micrograms, while the RI level is 10 micrograms for pregnant women, infants, people with dark skin and individuals that spend too little time in the sun.
Seniors in retirement homes and people from the age of 70 years are advised to take a 20 microgram per day supplement of vitamin D, but many scientists believe that the actual need for vitamin D in general is much higher, and they recommend anything from 30 to 100 micrograms daily.
Christian M. Girgis et al. Mice with myocyte deletion of vitamin D receptor have sarcopenia and impaired muscle function. Journal of Cachexia, Sarcopenia and Muscle, 2019
Weastmead Institute for Medical Research. Muscling in one role of vitamin D. ScienceDaily June 26. 2019
Jo Lewin. Can vitamin D relieve joint pain? MedicalNewsToday 2018
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