A study with 4,551 women of at least 69 years of age indicated that blood levels of vitamin D between 20.0 and 29.9 ng/ml are at the lowest risk of frailty, while levels above or below this range are associated with an increased likelihood of frailty in older women, according to findings published in the Journal of Clinical Endocrinology & Metabolism (JCEM).
In an accompanying editorial in the same journal, Clifford Rosen, MD, and JoAnn Manson, MD, DrPH, from the Maine Medical Center Research Institute and Brigham and Women’s Hospital, and Harvard Medical School, said the findings are consistent with other observational studies that “imply that optimal serum 25OHD concentrations for preventing frailty range between 20 and 30 ng/ml”.
Importantly, Rosen and Manson note the number of individuals with blood vitamin D levels over 30 ng/ml was relatively small, with the mean level of vitamin D measured as 23.2 ng/mL.
“The dose-response relationship, presence or absence of a threshold, and the possibility of harm at both lower and higher levels of vitamin D intake, require further study, particularly with randomized controlled trials,” wrote the Boston-based scientists.
“In the meantime, the [new] paper reminds us that maintenance of adequate serum 25OHD levels in our elderly population is clinically important and that, based on existing evidence, vitamin D supplementation should be targeted to reach levels (i.e. 20-29 ng/ml) that are safe as well as efficacious,” they added.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.
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.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
And the science supports maintaining adequate levels, with vitamin D deficiency in adults 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.
The new study, led by the University of Minnesota’s Kristine Ensrud, MD, supports the need for adequate levels. Over 4,500 women participated in the study, none of whom were considered frail at the start of the study. The researchers report that, in addition to the U-shaped relationship between vitamin D and frailty, women with the lower vitamin D levels at the start of the study were associated with an increased risk of frailty or death after 4.5 years of study.
"Evidence is lacking to support use of vitamin D supplementation for prevention of frailty and other outcomes including cancer or all-cause mortality," said Ensrud. "Our results indicate that well-designed large randomized trials of sufficient duration are needed to accurately quantify health effects of vitamin D supplementation, including whether or not supplementation reduces the incidence or progression of frailty in older adults."
Source: Journal of Clinical Endocrinology & Metabolism
December 2010, Volume 95, Pages 5266-5273, doi:10.1210/jc.2010-2317
“Circulating 25-Hydroxyvitamin D Levels and Frailty Status in Older Women”
Authors: K.E. Ensrud, S.K. Ewing, L. Fredman, M.C. Hochberg, J.A. Cauley, T.A. Hillier, S.R. Cummings, K. Yaffe, P.M. Cawthon for the Study of Osteoporotic Fractures Research Group
Editorial: Journal of Clinical Endocrinology & Metabolism
December 2010, Volume 95, Pages 5210-5212
“Frailty: A D-Ficiency Syndrome of Aging?”
Authors: C. J. Rosen and J. E. Manson