Obesity and vitamin D deficiency have both been recognized as major public health issues worldwide, and there is growing evidence that they are related, although the cause-effect relationship remains unclear. Could obesity be contributing to low circulating 25-hydroxyvitamin D concentrations? Alternatively, could low vitamin D status predispose to obesity? In this review, the relationship between low circulating 25-hydroxyvitamin D and obesity, and possible underlying reasons from both perspectives, is presented. One potential mechanism by which obesity could contribute to low serum 25-hydroxyvitamin D is adipose sequestration of vitamin D. On the other hand, adipose tissue has both the vitamin D receptor and the ability to synthesize 1,25-dihydroxyvitamin D, and there is evidence that vitamin D may regulate adipose tissue mass, differentiation and metabolism in ways that might contribute to obesity. Of particular interest, vitamin D deficiency is common both before and after bariatric surgery, and is often difficult to treat, particularly with the more malabsorptive procedures. Additional research is needed to elucidate the complex and multifaceted factors underlying the association between low circulating 25-hydroxyvitamin D and obesity, and to identify optimal treatment approaches in obese individuals and in bariatric surgical patients both before and after surgery.

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The Deltatrac Metabolic Monitor (DTC), one of the most popular indirect calorimetry systems for measuring resting metabolic rate (RMR) in human subjects, is no longer being manufactured. This study compared five different gas analysis systems to the DTC. Resting metabolic rate was measured by the DTC and at least one other instrument at three study sites for a total of 38 participants. The five indirect calorimetry systems included: MedGraphics CPX Ultima, MedGem, Vmax Encore 29 System, TrueOne 2400, and Korr ReeVue. Validity was assessed using paired t-tests to compare means while reliability was assessed by using both paired t-tests and root mean square calculations with F tests for significance. Within-subject comparisons for validity of RMR revealed a significant difference between the DTC and Ultima. Bland-Altman plot analysis showed significant bias with increasing RMR values for the Korr and MedGem. Respiratory exchange ratio (RER) analysis showed a significant difference between the DTC and the Ultima and a trend for a difference with the Vmax (p = 0.09). Reliability assessment for RMR revealed that all instruments had a significantly larger coefficient of variation (CV) (ranging from 4.8% to 10.9%) for RMR compared to the 3.0 % CV for the DTC. Reliability assessment for RER data showed none of the instrument CV's were significantly larger than the DTC CV. The results were quite disappointing, with none of the instruments equaling the within person reliability of the DTC. The TrueOne and Vmax were the most valid instruments in comparison with the DTC for both RMR and RER assessment. Further testing is needed to identify an instrument with the reliability and validity of the DTC.Correspondence and request for reprints: Dr. Dale Schoeller,

It is recommended that the lean soft tissue mass estimate with the fan-beam QDR 4500A be reduced by 5% and that for fat mass be increased by that same mass. This finding is particularly important because the National Health and Nutrition Examination Survey is using the QDR 4500A to assess body composition in a nationally representative sample of persons in the United States.