Researchers from the VU University Medical Center reported that vitamin D deficiency doubled the risk of an increase in functional limitations.
“The results of the present study are in line with the results of most studies on vitamin D status and physical performance, in which low vitamin D status was associated with low physical performance and its decline in individuals aged 65 years and older,” wrote the researchers in The Journal of Clinical Endocrinology & Metabolism.
“Because functional limitations are a predictor of adverse outcomes, further research is necessary to explore underlying mechanisms and the potential benefits of vitamin D supplements on functional status.”
The sunshine vitamin
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol.
Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
Vitamin D deficiency, which is defined as a status of less than 20 nanograms per milliliter (ng/mL) of 25-(OH)D, can cause a number of health issues, including rickets and other musculoskeletal diseases.
While previous studies have reported a link between vitamin D status and functional limitations, the data to date has been ‘contradictory’, wrote the authors, led by Evelien Sohl.
For the new study, Sohl and her co-workers analyzed data from 1,237 people aged 65 to 88, and 725 people aged 55 to 65. Functional limitations were classed as problems walking up and down stairs, problems dressing or undressing, difficulty getting into and out of a chair, difficulty cutting toenails, being unable to walk outside for five minutes without rest, and whether the subject could use transportation.
Long term effects
The results indicated that, for the older and younger groups, 56 and 30% of people, respectively, had at least one limitation. Vitamin D deficiency in the older group was related to significant increases in functional limitations after three years. For the younger group, vitamin D deficiency was linked to an increase in limitations after six years, they wrote.
“The mechanism of action in our study may be the positive influence of vitamin D on muscles, and a poor vitamin D status may cause functional limitations,” they said. “However, the previously found associations may be caused by, for example, less sunshine exposure due to mobility limitations.”
Sohl and her co-workers added that the vitamin may exert its effects via genomic and non-genomic pathways. Muscle cells have vitamin D receptors on their surface, and these can activate over 300 genes.
It has been known that vitamin D receptors exist on muscle cells. By binding to this receptor more than 300 genes can be activated.
“Although the current study is not designed to determine the direction of the relationship, the results of the longitudinal analyses, the known presence of vitamin D receptors on muscle cells, and the positive effects of vitamin D supplementation on muscle function at least suggest a potential positive effect of vitamin D on functional performance.”
Source: The Journal of Clinical Endocrinology & Metabolism
Published online ahead of print, doi: 10.1210/jc.2013-1698
“Vitamin D Status Is Associated With Functional Limitations and Functional Decline in Older Individuals”
Authors: E. Sohl, N. M. van Schoor, R. T. de Jongh, M. Visser, D. J. H. Deeg and P. Lips