Vitamin D deficiency and influence on muscles

Geschatte leestijd: 9 minutenVitamin D can increase muscle strength and possibly muscle mass. In winter, the chance of a vitamin D deficiency is greater, making extra intake advisable.

What is Vitamin D

With winter approaching, jars of vitamins and minerals are being pulled out of drawers again. Especially extra vitamin D can be very attractive in the cold months with short days and long nights. In this article, I will briefly discuss the different types and forms of vitamin D, but especially the influence of vitamin D on muscle strength and muscle mass.

Vitamin D2 and D3

Vitamin D is one of the four fat-soluble vitamins. Vitamin D occurs in many different forms, the most important of which are D2 and D3. Both are produced by the body with the help of ultraviolet light from the sun. However, this is not sufficient, so you still depend on food and possibly supplementation to get enough vitamin D _[1].

Vitamin D2 and D3 occur in several forms in the body: The inactive form cholecalciferol, the form in which the amount of vitamin D in the blood is measured calcifediol, and the active form calcitriol [2]. Although I will try to limit myself here to the concrete demonstrated effects of vitamin D and not its functioning in the body, it is important to know for further in this article that vitamin D is measured in the blood based on the amount of calcidiol.

Vitamin D deficiency

Determining a vitamin D deficiency can still be quite tricky. These reference values for calcidiol vary by country and institution. Besides the fact that the (exact) reference values differ, measurements are done in various ways, so the same person can hear different values about the same blood sample [3].

In the Netherlands, the reference values even differ per hospital, so it can be stated in one place that you have a vitamin D deficiency while elsewhere it is considered within the normal range [4]. Generally, everything below 50 nmol/L is seen as less than desired and everything below 25 nmol/L as a vitamin D deficiency [5 to 8].

Below 50 nmol/L, complaints (such as bone disorders) are more likely to occur when this vitamin D deficiency is prolonged. Below 25 nmol/L, the chances increase, as well as the chances of muscle diseases and problems with the parathyroid gland, which can lead to problems with calcium levels [9]. Based on 50 nmol/L as a minimum, more than 1 billion people worldwide have a vitamin D deficiency [10]. However, ideal values (if you look at, among other things, the effect on calcium transport and the amount of parathyroid hormone) are even higher, around 75-80 nmol/L [11].

Risk groups for vitamin D deficiency

In many cases where research is done on the effects of vitamins and minerals, comparisons are often made with a situation involving a deficiency. The group that has taken a certain supplement often scores better than the group that has not. This can involve the likelihood of a certain condition, but also regarding the influence on muscle strength, muscle mass, and body fat. This sometimes leads to unjustified intake of certain dietary supplements considering the fact that the likelihood of a deficiency of that vitamin or mineral is actually very small in practice. However, a vitamin D deficiency does occur regularly, especially in certain population groups.

Consider, for example, the elderly; almost half of those aged 65 and over have a deficiency [12]. Also, people with a dark skin color, whose pigment blocks more UV light, have a greater chance of a vitamin D deficiency. A rule of thumb here is that if you are dark enough not to burn in the sun, you have an increased risk of a deficiency. Also, think of Muslim women who wear covering clothing, resulting in less ultraviolet light from the sun reaching the skin.

Another “risk group” is formed by pregnant women. Pregnant and non-Western allochthonous? Then more than half of the mothers and newborns have a severe vitamin D deficiency [13].

In the Netherlands, sufficient vitamin D is only produced between May and September between 10:00 and 15:00 [14]. Therefore, the rest of the year it is important to ensure sufficient supplementation through healthy food. It is not very surprising that even among healthy young people, over 30% have a vitamin D deficiency [5]. This means that even as a healthy young person, you can benefit from taking extra vitamin D.

Vitamin D Increases Muscle Strength

A link has been established between vitamin D deficiency in those aged 65 and older and loss of muscle strength [15]. American researchers found that out of 976 elderly individuals, 28.8% of women and 13.6% of men had less than 25 nmol/l of calcidiol in their blood. A staggering 75% of women and 51% of men had less than 50 nmol/L. When the groups with less than 25 nmol/L were compared with those with more than 25 nmol/L, it was found that the latter group had stronger grip strength in their hands. The same was found when comparing the group with less than 50 nmol/l with the group with more than 50 nmol/L.

Vitamin D status was inversely associated with poor physical performance. Given the high prevalence of vitamin D deficiency in older populations, additional studies examining the association between vitamin D status and physical function are needed.

D.K. Houston, Wake Forest University School of Medicine

In a study involving not only the elderly but also men and women aged 20 to 76, a similar association between vitamin D and muscle strength was found [16].

Even when only the effect in younger people was examined, vitamin D was found to influence muscle strength. British researchers conducted a systemic review, comparing all relevant studies on this topic [17]. They ultimately found six relevant and well-conducted studies involving individuals aged 20 to 32. In some cases, such a study lasted for 4 weeks, while in others, it could last up to six months. There were also differences in the dosages used, but overall, these studies provided a good picture. In some studies, the subjects were athletes. This makes it even more interesting for avid fitness enthusiasts because this is more relevant than the results of a couch potato (who already achieves results by getting up).

In these studies, the participants’ performance during the squat, leg press, bench press, and chest press was examined. In the image below, you can see the results of the different studies. To the right of the line, you see the studies that showed a positive influence of vitamin D on muscle strength (the group receiving vitamin D was stronger than the control group). Above, you see the effects on the lower body, and below, the effects on the upper body. In both cases, vitamin D supplementation resulted in more strength, although the difference was greater in the lower body.

The researchers therefore conclude:

… suggesting vitamin D supplementation significantly increased muscle strength in the experimental group for upper and lower limbs. Vitamin D supplementation increases upper and lower limb strength. Further research should focus on its effect on muscle power, endurance, and maximal strength.

it may be necessary to increase serum concentrations above the optimal concentrations (>50 nmol/L (20 ng/ml)) of vitamin D in order to suitably improve muscle strength. Although all of the studies used managed to increase their subjects serum levels to adequate concentrations, none reported ‘optimal’ levels.”

Vitamin D and Muscle Mass

Even when we look at the effect on muscle mass, we see a possible positive influence. This was shown, for example, in a 2011 American study involving 311 men and 356 women aged 21 to 97 years (average 57 years). In addition to muscle strength (measured by leg extensions and grip strength), the researchers also measured muscle mass. When they looked at the amount of inactive vitamin D, calcidiol (also called hydroxyvitamin D or abbreviated 25-OH D₃₎, they saw no effect. However, when they looked at the active form calcitriol (also called 1α,25-dihydroxycholecalciferol, or abbreviated 1,25(OH)2D), they saw a positive correlation with muscle mass, especially in people younger than 65.

However, in subjects younger than 65 years, there was a statistically significant association between low 1,25(OH)₂D levels and low skeletal mass in both men and women.

I. Marantes, Department of Health Sciences Research, College of Medicine, Mayo Clinic

From a systemic review conducted by Belgian researchers, who consulted 30 studies involving a total of 5615 people (average age 61 years), no effect of vitamin D on muscle mass was found. Of the 30 studies, six focused on muscle mass (the rest on strength). In the image to the right, you can see the results. To the right of the line means the researchers showed a positive correlation, to the left of the line means a negative correlation.

The researchers concluded that there was no significant relationship between vitamin D and muscle mass.

It is important to note that in these studies, the inactive form calcidiol was measured, not the active form calcitriol. In the study above from the Mayo Clinic, we saw that the inactive form had no effect, but the active form did. The researchers cannot explain this difference.

Anyway: The influence on muscle strength seems greater and better demonstrated than the influence on muscle mass.

Vitamin D3 More Effective than D2

That vitamin D would have an effect on muscle strength and muscle mass is not very surprising if you consider the knowledge that there are vitamin D receptors in muscle fibers [2,18]. However, whether this is the case is not yet certain and has been disputed in a 2011 study [wang].

Receptors are like specific keyholes on cells. If a particular key (substance such as the active form of vitamin D in this case) fits into such a receptor, then such a substance can exert an effect on that cell. So, if vitamin D could “bind” with certain receptors in muscle fibers, it would mean that vitamin D could have a local effect on these muscle cells. These receptors in muscle fibers are known to be involved in protein synthesis, the production of new proteins that lead to muscle growth, so this could possibly account for the effect on muscle strength and potentially mass.

Supplementing your diet with vitamin D3 is much more effective than with vitamin D2 because vitamin D3 binds much more strongly to the vitamin D receptors [21,22].

However, according to researchers from the University of Wisconsin-Madison, the detection method for these presumed receptors may be incorrect [23]. If the effect of Vitamin D is not exerted locally in the muscle but elsewhere, this could also possibly explain why there is an effect on muscle strength but not on muscle mass.

Conclusion Vitamin D Deficiency

The risk of vitamin D deficiency is considerable, especially for certain risk groups and in winter when the body can produce less vitamin D. Various studies have shown that higher levels of vitamin D can lead to more muscle strength in both young and old individuals. Whether this also applies to muscle mass is unclear. It is also not certain whether vitamin D can bind to receptors in the muscles.

In the next part about Vitamin D, I will discuss its effect on fat burning. Additionally, I will address recommended daily amounts, desired levels in the blood, and how much vitamin D you should supplement to benefit optimally in terms of muscle strength and fat burning.

References

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