By now, we are aware of the importance of vitamin D. It has been shown to reduce the risk of a number of diseases, including cardiovascular disease, cancer, respiratory infections, tuberculosis, diabetes, and even multiple sclerosis.
And now, researchers have found that vitamin D can have some interesting benefits on overweight and obese adults. Specifically, they discovered that supplementing with vitamin D during resistance training improved muscle function and was associated with a reduced waist-to-hip ratio.
The study included 23 overweight or obese adults. The participants were randomly selected to consume either 4,000 IU of vitamin D3 or a placebo. To control for calcium intake, everyone took one 500 mg calcium supplement daily. Researchers also provided all participants with packets of sunscreen and instructed them to apply four packets daily to exposed skin.
All of the individuals participated in treadmill walking and eight resistance exercises: leg extension, leg flexion, leg press, hip adduction, hip abduction, chest press, seated row and lateral pull-down. Following a one-week acclimation period, each participant completed a supervised 12-week resistance exercise training program, three days a week for a total of 36 sessions.
The workout consisted of five minutes of treadmill walking and stretching to warm up, followed by three sets of each of the eight resistance exercises (eight reps for the first set, followed by 15 reps, or as many reps as possible until muscle failure, for the second two sets). To control for the timing of post-exercise caloric intake — which could affect the growth and development of muscle — all participants consumed a nutrition shake during the hour following each exercise session.
Researchers assessed the participants’ vitamin D status and body composition at baseline and following the 12-week study. They evaluated body composition using dual energy X-ray absorptiometry and vitamin D with blood tests. All participants also took an oral glucose tolerance test at baseline and following the intervention.
After analyzing the results, researchers discovered two major differences between the vitamin D group and the placebo group. First, during the intervention, peak power significantly increased at four weeks in the vitamin D group. In addition, there was an inverse association between vitamin D levels and waist-to-hip ratio. So, in essence, vitamin D supplementation improved muscular power in these overweight or obese participants within four weeks of starting the supplementation, and the elevated vitamin D levels led to greater losses in waist circumference.
No significant differences were seen in glucose tolerance or body composition between the two groups.
The Best Way to Get Your Vitamin D
Whether or not you have issues with your weight, research has shown time and time again that having sufficient levels of vitamin D is extremely important for all aspects of your health. Improved muscular performance is an added bonus to the already long list of health benefits associated with the intake of this critical nutrient.
The get your daily dose of vitamin D, you can spend 20 minutes outside every day and expose your unprotected skin to direct sunlight. (If you’ll be outside longer than that, then it is prudent to apply sunscreen after your initial 20-minute exposure.)
If it’s not feasible for you to get this amount of direct sunlight exposure every day, or if your doctor has advised you to avoid the sun without the use of sunscreen, then you can get your D by eating certain foods (like salmon, egg yolks, dark, leafy greens and fortified dairy products) or by taking a supplement.
Vitamin D is widely available in retail stores and online, and it is inexpensive. Make sure to look at the supplement facts box on the bottle’s label to verify the product contains vitamin D3 in the form of cholecalciferol — the form of vitamin D best absorbed and utilized by the human body.
While this study used a daily dosage of 4,000 IU, this amount is on the high end of what many medical societies consider a safe upper limit. For this reason, we recommend that adults consider daily dosage levels between 500 IU and 2,000 IU. (If you’re looking for a high-quality vitamin D supplement, you can click here.)
 Carrillo AE et al. Impact of vitamin D supplementation during a resistance training intervention on body composition, muscle function, and glucose tolerance in overweight and obese adults. Clinical Nutrition (2012 Sept 03) doi:10.1016/j.clnu.2012.08.014.