Levels of vitamin D in girls are often associated with their muscle strength

Girls with high blood levels of vitamin D are generally stronger, while the same relation is not seen in boys, according to a cohort study from Odense University Hospital in Denmark. The study is published in the Journal of Clinical Endocrinology and Metabolism. Nonetheless, all humans need adequate levels of vitamin D, as the nutrient has a number of other important functions in the body.

Vitamin D is primarily known for its role in bone and immune health, but most of the body’s organs and tissues have vitamin D receptors, and the same goes for muscle cells.
According to medical student Rada Faris Al-Javadi, who headed a new study, girls with low blood levels of vitamin D are 70 percent more likely to be among the weakest in a test of muscle strength. The researchers also found that the strongest girls had blood levels of vitamin D that were above 50 nmol/l. However, what surprised them the most was that they only observed the link between vitamin D and muscle strength in girls, not in boys.
The study did not show a relation between maternal vitamin D status during pregnancy or vitamin D concentrations in the umbilical cord at birth and muscle strength of the girls. Therefore, the scientists assume that vitamin D does not affect muscle strength prior to delivery and suggest that it is a direct effect.

Why is there a difference between girls and boys when it comes to vitamin D and muscle strength?

According to Henrik Thybo Christensen, a professor at Odense University Hospital and the University of Southern Denmark, the study does not explain why there is a difference between girls and boys in terms of vitamin D and muscle strength. However, he points to other studies that show how vitamin D increases levels of Insulin-like Growth Factor-1 (IFG-1) and that increases muscle strength. Levels of IGF-1 is already higher in boys, which may explain why an increase in affects muscle strength more in girls. Based on the current data, the scientists cannot conclude that girls will gain muscle strength simply by getting more vitamin D from sun exposure or the diet. Nonetheless, is appears that having adequate amounts of vitamin D in the blood may make a difference in the many girls who lack the nutrient in the first place.

The study from Odense

Eight hundred and eighty eight five year-old children from Odense (Denmark) participated in the cohort study. A standard grip strength test was applied to all children to measure their muscle strength. Four hundred and ninety nine of the study participants had their vitamin D levels measured (as 25-hydroxyvitamin D), and levels lower than 50 nmol/l were considered as low. The analysis was adjusted for height, weight, and fat percentage in order to make it statistically significant. In other words, the link between muscle strength and vitamin D has nothing to do with being overweight, and the link between muscle strength and vitamin D has nothing to do with whether girls prefer being indoors and are physically less active. The scientists measured the body’s fat percentage using skin folds.

Other studies of vitamin D and its influence on muscles

It has been known for long that vitamin D is important for bone health. The classic deficiency disease is rickets where the bones are soft and malformed. A number of earlier studies of people aged 20-74 years have shown that vitamin D is important for muscle strength in the legs and physical capability. Too little vitamin D may also have a negative impact on muscle function and physical strength before it affects the bones. In addition, a vitamin D deficiency may increase the risk of muscle pain.

References

Vitamin D level in girls associated with muscle strength. News Medical Life Sciences. June 14. 2018
https://www.news-medical.net/news/20180614/Vitamin-D-level-in-girls-associated-with-muscle-strength.aspx

Lars Rejnmark. Effects of Vitamin D on Muscle Function and Performance: A Review of Evidence from Randomized Controlled Trials. Ther. Adv Cronic Dis. 2011 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3513873/

Ana Sandoiu. High levels of vitamin D may improve muscle strength. MedicalNewsToday 2017
https://www.medicalnewstoday.com/articles/315863.php

Sarah E Tague. Vitamin D Deficiency Promotes Skeletal Muscle Hypersensitivity and Sensory Hyperinnervation. J Neurosci 2011 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3319727/

https://www.sundhed.dk/sundhedsfaglig/laegehaandbogen/endokrinologi/tilstande-og-sygdomme/knoglevaev-og-vitamin-d/d-vitamin-mangel/