For individuals 55 and older, vitamin D deficiency may increase the likelihood of having difficulty performing daily activities, a Dutch study showed.
In a cross-sectional analysis, serum 25-hydroxyvitamin D (25[OH]D) levels below 20 ng/mL -- compared with levels greater than 30 ng/mL -- were significantly associated with the presence of at least one limitation in individuals ages 55 to 65 (OR 2.1) and ages 65 to 88 (OR 1.7), according to Natasja van Schoor, PhD, of VU University Medical Center in Amsterdam, and colleagues.
And in a longitudinal analysis, vitamin D deficiency at baseline was also significantly associated with an increase of at least two limitations at 3 years for the older cohort (OR 2.0) and at 6 years for the younger cohort (OR 3.3), the researchers reported online in the Journal of Endocrinology & Metabolism.
"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," van Schoor and colleagues wrote, adding that further study is needed to determine the mechanisms.
In an interview, Michael Holick, PhD, MD, of Boston University, highlighted the need to find out whether vitamin D supplementation has an impact on function.
"It would be very nice to have a vitamin D intervention study so that you could actually demonstrate that those that were vitamin D deficient, if you made their blood level of 25-hydroxyvitamin D above 30 ng/mL, which is what is in fact recommended by the Endocrine Society practice guidelines, ... that you could improve neurocognitive function, as well as muscle function, and improve overall health and welfare of people as they're aging," he said.
Although vitamin D has been associated with positive effects on muscle mass and strength, as well as physical performance, few studies have looked at the relationship between vitamin D and self-reported physical functioning. But those that have been completed have yielded mixed results.
In the current study, van Schoor and colleagues analyzed data from two cohorts of the Longitudinal Aging Study Amsterdam (LASA), an ongoing study of Dutch individuals. The analysis included 725 individuals from the younger cohort (mean age 60) and 1,237 individuals from the older cohort (mean age 75.3).
The participants were asked about their ability to perform six functions of daily living:
Walking up and down 15 stairs without resting Dressing and undressing Sitting down in and standing up from a chair Cutting their toenails Walking outside for 5 minutes without resting Using personal or public transportation
More than half of the older cohort (56%) and 30% of the younger cohort reported at least one limitation at baseline. The percentage of individuals who reported an increase of at least two additional limitations during follow-up was 15% in the older cohort and 6% in the younger cohort at 3 years, and 20% and 8%, respectively, at 6 years.
The Netherlands sets the minimum serum level of 25(OH)D at 20 ng/mL for older persons, as does the Institutes of Medicine, while The Endocrine Society calls for 30 ng/mL as the minimum level.
The average serum 25(OH)D levels were 21.6 ng/mL in the older cohort and 22.7 ng/mL in the younger cohort. Deficient levels were seen in 48% of the older cohort and 41% of the younger cohort.
Vitamin D deficiency was associated with an increased likelihood of having a functional limitation (in a cross-sectional analysis) or having an increase in the number of limitations (in the longitudinal analysis) after adjustment for age, gender, body mass index, chronic diseases, education, and level of urbanization.
The association with an increase of at least two additional limitations was significant at 3 -- but not 6 -- years for the older cohort and at 6 -- but not 3 -- years for the younger cohort.
In the older cohort, other factors -- like normal aging and chronic disease -- have effects on functional decline over time, and with longer follow-up "vitamin D alone might not be discriminative anymore," according to the researchers.
On the other hand, they wrote, "Participants of the younger cohort were younger, and therefore they may have had more skills to compensate for an increase in the number of limitations due to a low vitamin D status in the first 3 years."
The authors acknowledged that the study was limited by the measurement of vitamin D at only one time point for most participants, the lack of information on diet and use of vitamin D supplements, and the uncertain generalizability to frailer populations.
LASA is largely supported by a grant from the Netherlands Ministry of Health, Welfare, and Sports, Directorate of Long-Term Care. An unconditional grant from Merck was received for part of the vitamin D measurements. The Netherlands Organization for Health Research and Development (ZonMw) provided grant support for writing the paper.
The authors reported that they had no conflicts of interest.
Published on : Friday, July 19, 2013
Category : Vitamin D
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