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Recent research published in the Journal of Clinical Endocrinology and Metabolism found that older adults with high physical activity and high vitamin D status at baseline had significantly lower increases in body fat over five years compared to adults with high physical activity, but low vitamin D status.
Low vitamin D status has been linked to obesity, low physical activity, and age related loss of muscle mass. However, randomized controlled trials have found mixed results regarding whether vitamin D supplementation increases muscle mass and fat loss.
In a previous study from 2010, researchers found that higher baseline physical activity is associated with increases of vitamin D status over several years independent of time spent outdoors. This evidence led the researchers to conclude that physical activity may be beneficial for vitamin D status.
As this evidence points to a relationship between physical activity and vitamin D status, might the two synergistically relate to changes in body fat and muscle? Recently, the same research team of the 2010 study investigated this question.
They enrolled 615 adults from the Tasmanian Older Adult Cohort (TASOAC). TASOAC selected 1,100 adults ages 50 to 79 in Southern Tasmania to identify risk factors associated with osteoarthritis.
At baseline, the researchers measured the participants’ vitamin D levels. Participants were defined as having high vitamin D status if their levels were at or above 20 ng/ml and low if they were less than 20 ng/ml.
To assess physical activity, participants used pedometers for seven days. If an adult walked an average of 10,000 steps or more per day, they were considered to have a high physical activity level. If an adult walked an average of less than 10,000 steps per day, they were considered to have a low physical activity level.
According to baseline physical activity and vitamin D status, each adult was categorized into one of four groups. The groups consisted of those who had high vitamin D status and high physical activity (high VD/high PA), low vitamin D status and high physical activity (low VD/high PA), low vitamin D status and low physical activity (low VD/low PA), or high vitamin D status and low physical activity (high VD/low PA).
A total of 148 participants were classified as high VD/high PA, 225 were classified as high VD/low PA, 80 were classified as low VD/high PA, and 162 were classified as low VD/low PA.
The researchers focused on several different outcomes associated with muscle mass and body fat. They wanted to know if physical activity and vitamin D status, combined or separately, influenced baseline total body fat, total body fat percentage, trunk fat or the fat stored in the torso, appendicular fat (AFM), and appendicular lean mass (ALM).
Here is what the researchers found at baseline:
- The low VD/low PA group had significantly lower physical activity than the high VD/low PA group.
- The high VD/high PA group had significantly lower average body fat, trunk fat, AFM and percentage ALM than all other groups (p < 0.001).
After five to six years, the researchers assessed the participants’ anthropometrics again (total body fat, total body fat percentage, trunk fat, AFM, and ALM) and compared them to baseline measurements of vitamin D and physical activity.
The researchers founds these results after five years:
- The high VD/high PA group experienced smaller increases in body fat and decreases in ALM compared to all other groups.
- The low VD/low PA experienced a greater decrease in lower-limb muscle quality compared to high VD/high PA.
It is important to emphasize that those with both high physical activity and high vitamin D status experienced less changes in body composition compared to those with high physical activity and low vitamin D status, suggesting vitamin D has a unique interaction with the physical activity level of an individual.
In a sub-analysis, the researchers compared vitamin D status to changes in body composition and muscle over the five years. They found that adults with a high vitamin D status at baseline had significant decreases in total body fat, AFM, and significant increases in weight adjusted ALM. Though, no significant association remained after adjusting for intensity of exercise.
The researchers concluded,
“The results from this prospective population-based study of community-dwelling older adults indicate that combined high vitamin D and PA status is associated with smaller gains in body fat and smaller decreases in muscle quality over five years.”
The researchers noted that the main limitation of their study was the loss of participants during the course of the study. The participants who were lost to follow up were less active and younger than the participants who continued in the study. This limits the generalizability of the study to healthy older adults.
Additionally, vitamin D levels and physical activity were not measured over time, which means we don’t know how changes in these measurements over the 5 years affected results seen.
While trials examining the interaction between vitamin D supplementation and physical activity and their effects on body fat and muscle are still needed, this study suggests the importance of moderate exercise outside during midday to get both physical activity and daily vitamin D.
Scott D. et al. Vitamin D and physical activity status: Associations with five-year changes in body composition and muscle function in community-dwelling older adults. The Journal of clinical endocrinology and metabolism