A recent randomized controlled trial published in American Journal of Clinical Nutrition concluded that vitamin D3 supplementation does not increase weight loss.
In recent years, there has been a lot of discussion on the role of vitamin D in weight. Previous research has found that vitamin D levels tend to be low in overweight and obese people. Researchers have wondered if low vitamin D levels cause obesity or if obesity causes low vitamin D levels. While increasing evidence points to obesity causing low vitamin D levels, a question remains on whether vitamin D supplementation can help in weight loss.
Recently, researchers from the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle conducted a randomized controlled trial to answer this question.
They enrolled 218 postmenopausal overweight or obese women into their trial. All women had vitamin D levels between 10-32 ng/ml.
The women were randomly assigned into two groups:
- The first group consisted of women who followed a weight loss program and took 2000 IU of vitamin D3 daily.
- The second group consisted of women who followed a weight loss program and took a daily placebo.
The weight loss program consisted of a reduced caloric diet and 225 minutes per week of moderate to vigorous cardio exercise.
After 12 months, weight loss along with changes in vitamin D levels, waist circumference, body fat percentage, and trunk fat mass were measured.
Here is what the researchers found:
- The change in weight was -8.4% in the placebo group compared to -8.2% in the supplemented group.
- The waist circumference change was -4.5 cm in the placebo group and -4.9 cm in the supplemented group.
- The change in body fat was -3.5% in the placebo group and -4.1% in the supplemented group.
- None of the differences in measurements between the two groups were significant.
The researchers then compared these weight loss measurements in women in the vitamin D group who had vitamin D levels at or above 32 ng/ml to women in the vitamin D group who did not have levels above 32 ng/ml.
Here is what they found:
- Women who became replete had a weight loss of -9.9% compared to women who did not with a weight loss of -6.2%.
- Women who became replete had a waist circumference change of -6.6 cm compared to a -2.5 cm change in women who did not.
- Women who became replete had a change of body fat of -9.9% compared to a -6.2% change in women who did not.
- Changes in waist circumference stayed significant and BMI became significant after adjusting for variables such as age, race, vitamin D and calcium intakes, and sun exposure.
The researchers discussed the discrepancies:
“Our observation that women randomly assigned to vitamin D supplementation who became replete (i.e., [vitamin D levels at or greater than] 32 ng/mL) lost more weight and had greater improvements in body composition compared with women who did not become replete suggests a potential threshold effect and highlights the importance of considering changes in nutrient status rather than only the mean magnitude of change.”
The design of the study was strong due to it being a double blind randomized controlled trial. In addition, the study included a large population sample along with a long time frame. Nonetheless, the researchers may have been able to obtain more conclusive data if they had used higher doses of vitamin D and included participants with a lower vitamin D status at baseline.
This trial shows the potential impact of vitamin D supplementation on weight loss. While the supplementation itself did not affect weight loss, repletion of vitamin D levels (levels at or above 32 ng/ml) did. Further research is needed to clarify these effects with participants that have vitamin D levels at or above this marker.