Older adults with low levels of the sunshine vitamin had a 30% increased risk of mobility limitations, according to results published in the Journal of Gerontology: Medical Sciences.
"About one-third of older adults have low vitamin D levels," said lead author Denise Houston, PhD, RD, from Wake Forest’s Department of Geriatrics and Gerontology. "It's difficult to get enough vitamin D through diet alone and older adults, who may not spend much time outdoors, may need to take a vitamin D supplement."
Current recommendations call for people over age 70 to get 800 International Units (IU) of vitamin D daily in their diet or supplements. Such recommendations are based solely on vitamin D's effects on bone health, said Houston.
"Higher amounts of vitamin D may be needed for the preservation of muscle strength and physical function as well as other health conditions," she said. "However, clinical trials are needed to determine whether increasing vitamin D levels through diet or supplements has an effect on physical function."
Houston and her co-workers analyzed data from 2,099 elderly people participating in the Health, Aging and Body Composition study. "This is one of the first studies to look at the association of vitamin D and the onset of new mobility limitations or disability in older adults,” she said.
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(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 in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases.
There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.
Results showed that 29% of participants had blood levels of vitamin D, measured as 25- hydroxyvitamin D (25(OH)D), below 50 nmol/L and 36% had 25(OH)D levels between 50 and 75 nmol/L.
Both groups were at a significantly higher risk of developing mobility limitation and mobility disability over 6 years of study, compared with participants with vitamin D levels over 75 nmol/L.
"We observed about a 30 percent increased risk of mobility limitations for those older adults who had low levels of vitamin D, and almost a two-fold higher risk of mobility disability," said Houston.
The vitamin plays an important role in muscle function, she added, so it is biologically plausible that low levels of the vitamin could result in the onset of decreased lower muscle strength and physical performance.
“Given that remediation of low 25(OH)D can be done easily and inexpensively with vitamin D supplements, definitive trials of vitamin D supplementation are needed to determine whether increasing 25(OH)D in older adults can improve or prevent further declines in physical function and mobility in particular,” concluded the researchers.
Source: Journal of Gerontology: Medical Sciences
Published online ahead of print, doi: 10.1093/gerona/gls136
“Low 25-Hydroxyvitamin D Predicts the Onset of Mobility Limitation and Disability in Community-Dwelling Older Adults: The Health ABC Study”
Authors: D.K. Houston, R.H. Neiberg, J.A. Tooze, D.B. Hausman, et al.