Vitamin d and physical activity status: associations with five-year changes in body composition and muscle function in community-dwelling older adults.
BACKGROUND
High vitamin D and physical activity (PA) levels are independently associated with improved body composition and muscle function in older adults.


OBJECTIVE
The objective of this study was to investigate the interaction of 25-hydroxyvitamin D (25OHD) and PA status in maintenance of body composition and muscle function in older adults.


METHODS
This was a 5-year prospective population-based study of Australian community-dwelling older adults.


METHODS
Participants in the study included 615 community-dwelling volunteers aged 50 years old or older [61.4 ± 6.9 (mean ± SD) y; 48% female] randomly selected from electoral rolls and categorized according to baseline serum 25OHD (≥ or <50 nmol/L) and PA (≥ or <10,000 pedometer determined steps/d) levels as follows: high 25OHD and high PA (VitD+PA+); high 25OHD and low PA (VitD+PA-); low 25OHD and high PA (VitD-PA+); and low 25OHD and low PA (VitD-PA-). A subset of 518 participants completed accelerometer assessments during follow-up.


METHODS
Changes in dual-energy X-ray absorptiometry-assessed body composition and lower-limb muscle function were measured.


RESULTS
VitD+PA+ had significantly smaller increases in body fat over 5 years compared with other groups (all P < .05). Higher baseline pedometer-determined PA resulted in declines in total body fat (β = -.23 kg per 100 steps/d, P = .001) over 5 years for participants with high 25OHD but not those with low 25OHD (P > .05). Among participants with accelerometer data, these associations were generally mediated by higher levels of moderate/vigorous PA.


CONCLUSIONS
High vitamin D status appears to enhance PA-related declines in body fat during aging, but the mechanism may be greater amounts of outdoor moderate/vigorous PA rather than a direct effect of 25OHD.
NorthWest Academic Centre and Australian Institute for Musculoskeletal Science (D.S., P.R.E., K.M.S.), The University of Melbourne and Western Health, Sunshine Hospital, St Albans, Victoria 3021, Australia; School of Clinical Sciences (P.R.E.), Monash Medical Centre, Monash University, Clayton, Victoria 3168, Australia; and Menzies Research Institute (D.A., T.W., G.J.), University of Tasmania, Hobart, Tasmania 7000, Australia.
David
D
Scott
Peter R
PR
Ebeling
Kerrie M
KM
Sanders
Dawn
D
Aitken
Tania
T
Winzenberg
Graeme
G
Jones
D000368:Aged; D000375:Aging / Q000502:physiology*; D001315:Australia; D001823:Body Composition / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011446:Prospective Studies; D012111:Residence Characteristics; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
D014807:Vitamin D; C104450:25-hydroxyvitamin D