Dr. Shalamar Sibley from the University of Minnesota in Minneapolis told the conference that, "While vitamin D deficiency is associated with obesity, there are limited data on the temporal relationship between vitamin D and weight loss -- an important step in establishing a cause-effect link between vitamin D deficiency and obesity."

Dr. Sibley and colleagues investigated the temporal relationship between baseline vitamin D levels and subsequent weight loss success in 38 overweight and obese men and women.

They measured plasma vitamin D (25-hydroxyvitamin D and 1,25-dihydroxyvitamin D) concentrations before and after an 11-week weight loss intervention consisting of a 750 calorie per day deficit from estimated total daily calorie needs. They used dual-energy X-ray absorptiometry and computed tomography to measure body composition and fat distribution.

On average, vitamin D levels in study subjects were in the insufficient range.

According to the investigators, in separate models adjusted for gender, baseline (pre-diet) 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels predicted subsequent weight loss success (p = 0.020 and p = 0.015, respectively) on a reduced calorie diet. For each 1-ng/mL increase in level of 25-hydroxyvitamin D, obese patients lost almost half a pound (0.196 kg) more on their calorie-restricted diet. For each 1-ng/mL increase in 1,25-dihydroxyvitamin D, subjects lost nearly one-quarter pound (0.107 kg) more.

"Abdominal fat loss, in particular, tended to be related to baseline vitamin D concentrations, with the effect being stronger with the active form of vitamin D," Dr. Sibley reported. "Vitamin D status did not predict lean body mass changes, so there was relative preservation of lean tissue."

The researchers say studies are needed to confirm these findings and define underlying mechanisms.

"If it is established," Dr. Sibley said, "that vitamin D does indeed synergistically contribute to standard weight loss approaches, such as a reduced calorie diet, then identification and treatment of inadequate vitamin D status could ultimately have a large public health impact on the obesity epidemic. Our findings suggest that vitamin D may play an important role in promoting optimal weight management," she concluded.

Presented at The Endocrine Society's annual meeting in Washington, D.C.June 2009