Vitamin D is considered to be a hormone as well as a vitamin. It regulates calcium absorption and is important for bone health. Levels of vitamin D vary based on weight, ethnicity, age, and geography. Lab and epidemiological studies have claimed that vitamin D could be protective against certain cancers and cardiovascular disease. It is well known that overweight and obesity increases risk for cancer and cardiovascular disease. Researchers have observed that obese individuals are often vitamin D deficient and wonder if there is an underlying mechanism.
The purpose of this study was to examine whether there is a link between obesity and low circulating concentrations of vitamin D.
The study was done on 439 obese and overweight postmenopausal women divided into four groups. There were three intervention groups and one control.
The first group was the diet modification group consisting of 118 women. With the help of dietitians, these women reduced their calories between 1200-2000 calories to achieve a weight loss goal of ten percent. The women attended group meetings, and kept daily food logs for six months or until their weight loss goal was achieved. The second intervention group was the exercise group and consisted of 117 women. They participated in aerobic exercise for 45 minutes five days a week. The third and final intervention group included both diet and exercise. Lastly, there was a control group consisting of 87 women who had no diet or exercise intervention.
It was discovered that circulating vitamin D levels increased in all the intervention groups when weight loss occurred. The greater the weight loss, the greater the increase in blood levels of vitamin D.
The authors of the study imply that there may be a threshold of weight loss relevant to the affects of vitamin D levels. They recommend studying a group that achieves a weight loss of greater that 15%. The study was limited to non-Hispanic white women, and they did not account for sun exposure in the study.
Low blood levels of vitamin D are associated with obesity and greater waist circumference, and weight loss increases blood levels of vitamin D.
The full article title is “Effects of Weight Loss on Serum Vitamin D in Postmenopausal Women.” It is in The American Journal of Clinical Nutrition (2011): 94-103. The authors are C. Mason, L Xiao, I Imayama, CR. Duggan, C Bain, KE Foster-Schubert, A Kong, KL Campbell, CY Wang, ML Neuhouser, L Li, RW Jeffrey, and K Robien.
Written by Ayesha Elbanna and Stephanie Sawiris, Dept. Nutritional Sciences, Rutgers University-NewBrunswick Edited by SA Shapses, PhD, RD