Writing in the Journal of Clinical Endocrinology & Metabolism, researchers from the University of Manchester report that the vitamin D levels of 99 adolescent girls between the ages of 12 and 14 was positively associated with muscle power and force.
The study adds to an ever-growing body of science supporting the benefits of adequate vitamin D levels throughout life, with deficiency of the vitamin linked to osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases.
“We know vitamin D deficiency can weaken the muscular and skeletal systems, but until now, little was known about the relationship of vitamin D with muscle power and force,” said lead author of the study Kate Ward, PhD.
“Our study found that vitamin D is positively related to muscle power, force, velocity and jump height in adolescent girls.”
While the vitamin can be produced by the body on exposure to sunlight, other studies have shown that large sections of the population may be vitamin D insufficient or deficient.
Indeed, according to a study from the US in July 2007 (American Journal of Clinical Nutrition, Vol. 86, pp. 150-158), about 55 per cent of seemingly healthy adolescents may be vitamin D deficient. A similar study from Britain in 2006 reported that over 70 per cent of seemingly healthy teenage girls might be vitamin D deficient (Archives of Disease in Childhood, Vol. 91, pp. 569-572).
Ward and her co-workers recruited the adolescent girls at an inner city, multi-ethnic school in Manchester. Blood samples showed that the average vitamin D levels were 21.3 nanomoles per litre (nmol/L), and ranged from 2.5 to 88.5 nmol/L. While none of the girls had any physical symptoms of vitamin D deficiency, the researchers report that 75 per cent of the screened population had low 25(OH)D levels.
Muscle strength and force were measured using technique called jumping mechanography, which derives power and force measurements from a subject’s performance in a series of jumping activities.
The researchers report that girls without vitamin D deficiency performed significantly better in jumping test.
“These data highlight the importance of vitamin D status on muscle function in adolescent girls. Sub-optimal force might have implications for long-term bone development,” wrote the researchers.
“The long-term implications of these observations require further study,” they concluded.
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 hydroxylated in the liver and kidneys to form 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.
The other researchers were affiliated with the Longsight Health Centre in Manchester, the University of Manchester, Novotec Medical GmBH in Pforzheim, Germany, and Saint Mary’s Hospital for Women & Children in Manchester.
Source: Journal of Clinical Endocrinology & MetabolismFebruary 2009“Vitamin D Status and Muscle Function in Post-Menarchal Adolescent Girls”Authors: K.A. Ward, G. Das, J.L. Berry, S.A. Roberts, R. Rawer, J.E. Adams, Z. Mughal