Prevalence and Persistence of Vitamin D Deficiency in Biliopancreatic Diversion Patients: A Retrospective Study

Bone Response to Weight Loss Following Bariatric Surgery

Obesity is a global health challenge that warrants effective treatments to avoid its multiple comorbidities. Bariatric surgery, a cornerstone treatment to control bodyweight excess and relieve the health-related burdens of obesity, can promote accelerated bone loss and affect skeletal strength, particularly after malabsorptive and mixed surgical procedures, and probably after restrictive surgeries. The increase in bone resorption markers occurs early and persist for up to 12 months or longer after bariatric surgery, while bone formation markers increase but to a lesser extent, suggesting a potential uncoupling process between resorption and formation. The skeletal response to bariatric surgery, as investigated by dual-energy X-ray absorptiometry (DXA), has shown significant loss in bone mineral density (BMD) at the hip with less consistent results for the lumbar spine. Supporting DXA studies, analyses by high-resolution peripheral quantitative computed tomography (HR-pQCT) showed lower cortical density and thickness, higher cortical porosity, and lower trabecular density and number for up to 5 years after bariatric surgery. These alterations translate into an increased risk of fall injury, which contributes to increase the fracture risk in patients who have been subjected to bariatric surgery procedures. As bone deterioration continues for years following bariatric surgery, the fracture risk does not seem to be dependent on acute weight loss but, rather, is a chronic condition with an increasing impact over time. Among the post-bariatric surgery mechanisms that have been claimed to act globally on bone health, there is evidence that micro- and macro-nutrient malabsorptive factors, mechanical unloading and changes in molecules partaking in the crosstalk between adipose tissue, bone and muscle may play a determining role. Given these circumstances, it is conceivable that bone health should be adequately investigated in candidates to bariatric surgery through bone-specific work-up and dedicated postsurgical follow-up. Specific protocols of nutrients supplementation, motor activity, structured rehabilitative programs and, when needed, targeted therapeutic strategies should be deemed as an integral part of post-bariatric surgery clinical support.

Understanding the Experience of Osteoporosis Risk in Bariatric Surgical Patients

Despite what is known about risk factors, preventive treatment, and increased prevalence of fragility fractures in post-bariatric surgical patients, little is known about how patient perspectives of osteoporosis risk inform their commitment to bone health. The purpose of this study was to examine the lived experience of osteoporosis risk in people who have had bariatric surgery. Interpretive phenomenology was used to explore osteoporosis from the perspectives of patients who have had bariatric surgery. Eligibility criteria included female, age older than 18 years, and able to understand and speak English. This research provided an understanding of the risk of osteoporosis from the constructed realities and experiences of those who have had bariatric surgery. Participants in this study incorrectly felt they had little to no risk for osteoporosis after bariatric surgery. Patients need to be aware of an increased risk for osteoporosis leading to the potential for fragility fractures after bariatric surgery; nurses are well positioned to enhance osteoporosis prevention efforts in this population through pre- and postoperative education.

Effects of Post-operative Nutritional Disorders Following Bariatric Surgery on Health Care Cost and Use

PURPOSE

Risk of nutritional disorders (NDs) in bariatric surgical patients has led to guideline recommendations for pre- and post-operative nutrient deficiency screening. The aim of this study was to identify baseline factors associated with incident NDs and, in addition, to explore possible differences in health care spending and use between patients with and without incident NDs following bariatric surgery.

MATERIALS AND METHODS

Using data linked with a state-wide bariatric surgical registry and a state-wide claims database, subjects who underwent bariatric surgery between July 1, 2013, and December 31, 2015, were identified. Incident NDs and health care cost and use outcomes following 1 year from surgery were extracted from the claims data. Logistic regression was used to identify baseline factors associated with incident NDs. Zero-inflated negative binomial regression and generalized linear regression were used to estimate health care cost and use outcomes.

RESULTS

A total of 3535 patients who underwent bariatric surgery were identified. Of these patients, those without continuous health insurance enrollment (n=1880), having prevalent (pre-surgery) NDs (n=461), and missing baseline BMI (n=41) were excluded. Of patients analyzed (n=1153), about 30% had incident NDs, with a mean (SD) age and BMI at surgery of 46 (12) years and 48 (9.2) kg/m², respectively. Patients with one incident ND had higher total health care spending (coefficient=$41118, p-value<0.01) and ED visits (IRR=1.86, p-value<0.01).

CONCLUSION

Those without pre-operative NDs may have a higher chance of having NDs post-operatively. Taking multivitamins and continues monitoring are necessary to prevent any negative outcomes related to post-operative NDs.

Consensus statement from 2nd International Conference on Controversies in Vitamin D

The 2nd International Conference on Controversies in Vitamin D was held in Monteriggioni (Siena), Italy, September 11-14, 2018. The aim of this meeting was to address ongoing controversies and timely topics in vitamin D research, to review available data related to these topics and controversies, to promote discussion to help resolve lingering issues and ultimately to suggest a research agenda to clarify areas of uncertainty. Several issues from the first conference, held in 2017, were revisited, such as assays used to determine serum 25-hydroxyvitamin D [25(OH)D] concentration, which remains a critical and controversial issue for defining vitamin D status. Definitions of vitamin D nutritional status (i.e. sufficiency, insufficiency and deficiency) were also revisited. New areas were reviewed, including vitamin D threshold values and how they should be defined in the context of specific diseases, sources of vitamin D and risk factors associated with vitamin D deficiency. Non-skeletal aspects related to vitamin D were also discussed, including the reproductive system, neurology, chronic kidney disease and falls. The therapeutic role of vitamin D and findings from recent clinical trials were also addressed. The topics were considered by 3 focus groups and divided into three main areas: 1) "Laboratory": assays and threshold values to define vitamin D status; 2) "Clinical": sources of vitamin D and risk factors and role of vitamin D in non-skeletal disease and 3) "Therapeutics": controversial issues on observational studies and recent randomized controlled trials. In this report, we present a summary of our findings.

Serum Parathyroid Hormone and 25-Hydroxyvitamin D Concentrations Before and After Biliopancreatic Diversion

BACKGROUND

Biliopancreatic diversion with duodenal switch (BPD-DS) decreases vitamin D and calcium absorption, which may result in secondary hyperparathyroidism. This study aimed at evaluating the prevalence of vitamin D deficiency and secondary hyperparathyroidism before and after BPD-DS.

METHODS

A retrospective analysis of patients who had undergone BPD-DS at a tertiary bariatric center between 2003 and 2010 and for whom simultaneous measurements of serum 25-hydroxyvitamin D and parathyroid hormone were available within 5 years post-op was performed. The prevalence of vitamin D deficiency (< 20 ng/ml) and secondary hyperparathyroidism (> 65 pg/mL) at different time points was calculated.

RESULTS

Included were 1436 patients (mean ± SD, age 42.7 ± 10.4 years; BMI 51.5 ± 8.6 kg/m²; 69.8% women). Prevalence of vitamin D deficiency decreased up to 6-12 months after surgery (from 35.8% at baseline down to 6-9%) then rose progressively, plateauing at 15.5% after 36 months. Prevalence of hyperparathyroidism was 28.5% before surgery and rose progressively after surgery, reaching 68.6% at 5 years. Mean serum corrected calcium increased from 0 to 6 months then decreased up to 36 months. Preoperatively, the prevalence of hypocalcemia was 7.3%. It increased after 12 months, attaining 26.9% at 48 months.

CONCLUSIONS

Prevalence of vitamin D deficiency and secondary hyperparathyroidism is high before BPD-DS. Despite a low prevalence of vitamin D deficiency after surgery, prevalence of hyperparathyroidism increased steadily 1 year after surgery, preceded by a decrease in serum calcium. Factors explaining the high prevalence of secondary hyperparathyroidism after BPD-DS and its long-term impact on bone health should be addressed.

For whom the bell tolls? It is time to retire the classic BPD (bilio-pancreatic diversion) operation

With the culture of safety and lowering risks that took place 20 years ago, sleeve gastrectomy has emerged as a procedure of choice. Hence, for super- and super-super-obese patients, there is a tendency these days to perform surgeries in 2 stages, and sleeve is the procedure of choice. Because sleeve is not part of a classic bilio-pancreatic diversion, it is unlikely that this operation will be done as a second stage, making this operation obsolete.

Hypovitaminosis D: Is It Time to Consider the Use of Calcifediol?

Hypovitaminosis D is becoming a notable health problem worldwide. A consensus exists among several different medical societies as to the need for adequate levels of vitamin D for bone and general health. The correct method by which to restore normal vitamin D levels is still a matter of debate. Although cholecalciferol remains the most commonly distributed form of vitamin D supplementation worldwide, several drugs with vitamin D activity are available for clinical use, and making the correct selection for the individual patient may be challenging. In this narrative review, we aim to contribute to the current knowledge base on the possible and appropriate use of calcifediol-the 25-alpha-hydroxylated metabolite-in relation to its chemical characteristics, its biological properties, and its pathophysiological aspects. Furthermore, we examine the trials that have aimed to evaluate the effect of calcifediol on the restoration of normal vitamin D levels. Calcifediol is more soluble than cholecalciferol in organic solvents, due to its high polarity. Good intestinal absorption and high affinity for the vitamin-D-binding protein positively affect the bioavailability of calcifediol compared with cholecalciferol. In particular, orally administered calcifediol shows a much shorter half-life than oral cholecalciferol. Most findings suggest that oral calcifediol is about three- to five-fold more powerful than oral cholecalciferol, and that it has a higher rate of intestinal absorption. Accordingly, calcifediol can be particularly useful in treating diseases associated with decreased intestinal absorption, as well as obesity (given its lower trapping in the adipose tissue) and potentially neurological diseases treated with drugs that interfere with the hepatic cytochrome P-450 enzyme system, resulting in decreased synthesis of calcifediol. Up to now, there has not been enough clinical evidence for its use in the context of osteoporosis treatment.

Impact of bariatric surgery on bone tissue

The important prevalence and morbidity of obesity has generated an increase in bariatric surgery. It has a positive effect in obesity-related comorbidities. However, it's detrimental to bone health. The underline pathophysiological mechanisms are complex and heterogeneous. The knowledge of these factors may lead us to develop an adequate therapeutic intervention.

Calcifediol Rather Than Cholecalciferol for a Patient Submitted to Malabsortive Bariatric Surgery: A Case Report

Vitamin D deficiency following malabsorptive bariatric surgery can lead to osteomalacia. We report a patient with severe vitamin D deficiency following malabsorptive bariatric surgery successfully treated with calcifediol but not cholecalciferol. A 40-year-old woman, submitted to biliopancreatic diversion 20 years before and chronically treated with 50,000 IU cholecalciferol weekly, was admitted to our Endocrine Unit because of severe lower back pain, muscle weakness, and generalized muscular hypotrophy, associated with hypocalcemia and elevated PTH levels. Initial evaluation revealed low serum albumin, low albumin-corrected serum calcium (7.36 mg/dL), high serum PTH (240 pg/mL), bone-specific alkaline phosphatase (125 μg/L) and 1,25-dihydroxyvitamin D (112 pg/mL) concentrations, undetectable serum 25-hydroxyvitamin D (<7 ng/mL), and evidence of reduced liver function. Bone mineral density was markedly low. Normocalcemia was initially restored with intravenous albumin and calcium gluconate. Treatment with calcitriol (0.5 μg three times daily) and oral calcium carbonate (1000 mg daily) was simultaneously started and cholecalciferol was replaced with calcifediol [125 μg (5000 IU) daily)]. During follow-up the calcifediol dose was progressively tapered to 25 μg (1000 IU) daily and the calcitriol dose was progressively reduced and finally withdrawn. Serum albumin and other biochemical parameters normalized, bone mineral density significantly increased, and the patient's clinical conditions progressively improved, with a substantial recovery of autonomy. Serum vitamin D binding protein at the last observation was in the normal range. Our data suggest that calcifediol might be more efficacious than cholecalciferol for prevention and treatment of vitamin D deficiency in patients treated by malabsorptive bariatric surgery.

Comparison of two methods for measuring 25-OH vitamin D in the follow-up of patients after bilio-pancreatic diversion bariatric surgery

OBJECTIVE

Our objective was to compare the ECLIA from Roche versus the LC-MS/MS method for quantitation of serum 25-hydroxy-vitamin D in patients who have undergone bariatric surgery.

DESIGN AND METHODS

Cross-sectional and correlational studies were performed on three different groups for the 25-OH-D levels quantitated by both methods. The control group of apparently healthy subjects was randomly selected in a clinical chemistry laboratory. Test groups were patients who had undergone bilio-pancreatic diversion (BPD) and were supplemented either with vitamin D₂ or with vitamin D₃. The number of samples per group was established according to the CLSI recommendation protocol (EPO9-A2-IR).

RESULTS

The agreement of LC-MS/MS with the Roche method was acceptable in the apparently healthy subjects group and in the post-BPD D₃-supplemented group with an average bias of -1.7% and -9.2%, respectively. However, this agreement was unacceptable in the post-BPD D₂-supplemented group with an average bias of -45.3%. The LC-MS/MS enabled us to detect four patients who had excess vitamin D or poisoning with vitamin D for which it was necessary to stop the supplementation with vitamin D in the D₂ -supplemented group.

CONCLUSION

Despite the apparent good agreement between the Roche method and LC-MS/MS in the healthy subjects group and in the post-DBP D₃-supplemented patient group, a considerable bias seems to exist, particularly in the presence of D₂. The LC-MS/MS method is therefore the most accurate method to follow the vitamin D₂ -supplemented bariatric population.

Changes in Bone Metabolism in Morbidly Obese Patients After Bariatric Surgery: A Meta-Analysis

BACKGROUND

The aim is to evaluate via meta-analysis bone metabolism and bone mineral density (BMD) in morbidly obese patients before and after bariatric surgery.

METHODS

We searched Medline, EMBASE, and the Cochrane Library for relevant studies published before January 2014. The following outcomes were evaluated: serum calcium, serum parathyroid hormone (PTH), serum 25-hydroxyvitamin D [25(OH)D], serum or urinary N-telopeptide (NTX), bone-specific alkaline phosphatase (BSAP), and bone mineral density (BMD).

RESULTS

Ten studies, including 344 patients, met our inclusion criteria. Results showed a significant decrease in serum calcium (MD = -0.10, 95 %CI -0.14 to -0.07, P < 0.00001) and increase in serum PTH (MD = 12.41, 95 %CI 6.51 to 18.31, P < 0.00001) but no significant difference in serum 25(OH)D (MD = 1.35, 95 %CI -1.12 to 3.83, P = 0.28) following bariatric surgery. There were significant increases in serum or urinary NTX (MD = 18.49, 95 %CI 3.33 to 33.66, P = 0.02) and BSAP (MD = 7.47, 95 %CI 0.21 to 14.72, P = 0.04) but a significant decrease in BMD (MD = -0.08, 95 %CI -0.13 to -0.04, P < 0.00001) after bariatric surgery.

CONCLUSION

BMD was significantly decreased, while bone turnover was elevated, and bone remodeling was accelerated following bariatric surgery. Basal bone metabolism should be evaluated preoperatively. To prevent secondary hyperparathyroidism and bone loss, calcium and vitamin D should be monitored closely and supplemented accordingly after the surgery.

Hypovitaminosis D in bariatric surgery: A systematic review of observational studies

BACKGROUND

Obesity is a public health problem that carries global and substantial social and economic burden. Relative to non-surgical interventions, bariatric surgery has the most substantial and lasting impact on weight loss. However, it leads to a number of nutritional deficiencies requiring long term supplementation.

OBJECTIVES

The aims of this paper are to review 25-hydroxyvitamin D [25(OH)D] status pre and post bariatric surgery, describe the dose response of vitamin D supplementation, and assess the effect of the surgical procedure on 25(OH)D level following supplementation.

METHODS

We searched Medline, PubMed, the Cochrane Library and EMBASE, for relevant observational studies published in English, from 2000 to April 2015. The identified references were reviewed, in duplicate and independently, by two reviewers.

RESULTS

We identified 51 eligible observational studies assessing 25(OH)D status pre and/or post bariatric surgery. Mean pre-surgery 25(OH)D level was below 30ng/ml in 29 studies, and 17 of these studies showed mean 25(OH)D levels ≤20ng/ml. Mean 25(OH)D levels remained below 30ng/ml following bariatric surgery, despite various vitamin D replacement regimens, with only few exceptions. The increase in post-operative 25(OH)D levels tended to parallel increments in vitamin D supplementation dose but varied widely across studies. An increase in 25(OH)D level by 9-13ng/ml was achieved when vitamin D deficiency was corrected using vitamin D replacement doses of 1100-7100IU/day, in addition to the usual maintenance equivalent daily dose of 400-2000IU (total equivalent daily dose 1500-9100IU). There was no difference in mean 25(OH)D level following supplementation between malabsorptive/combination procedures and restrictive procedures.

CONCLUSION

Hypovitaminosisis D persists in obese patients undergoing bariatric surgery, despite various vitamin D supplementation regimens. Further research is needed to determine the optimal vitamin D dose to reach desirable 25(OH)D levels in this population, and to demonstrate whether this dose varies according to the surgical procedure.

Effects of omega-loop gastric bypass on vitamin D and bone metabolism in morbidly obese bariatric patients

BACKGROUND

Bariatric patients often suffer from nutrient deficiencies. Little is known about vitamin D levels and bone metabolism in patients undergoing omega-loop gastric bypass (OLGB). We, therefore, evaluated parameters of vitamin D metabolism preoperatively and during the first postoperative year.

METHODS

Within our cohort study, we retrospectively evaluated the respective parameters pre-, 3, 6, and 12 months postoperatively in patients with OLGB, between February 2011 and February 2013.

RESULTS

In patients [n = 50; age 46 (15) years, mean (SD); 12 male, 38 female] BMI was 45.4 (6.6) kg/m(2) preoperatively and decreased to 29.1 (3.8) kg/m(2) after 12 months, corresponding to a total body weight loss of 36 %. Preoperatively, the prevalence of vitamin D deficiency was 96 and 30 % demonstrated elevated parathyroid hormone yielding a prevalence of secondary hyperparathyroidism of 17 %. Postoperatively, subjects received individually adjusted vitamin D3 supplementation (95 % CI 200-3000 IU/day), according to the available guidelines at that time. Nevertheless, every third patient was vitamin D deficient at 12 months (80 %). In patients with preoperative BMI >45 vs. <45 kg/m(2), we observed a 3-fold higher risk for vitamin D deficiency over 12 months [OR = 3.10, 95 % CI (1.01-9.51), p = 0.048].

CONCLUSIONS

To avoid vitamin D deficiency, morbidly obese patients, particularly those with higher preoperative BMI, should be regularly screened pre- and postoperatively. Standard postsurgical supplementation has not been adequate to restore 25-OHD status and current guidelines are not very specific in terms of timing and dosing of vitamin D3 supplementation. Consequently, further trials to enhance the evidence on vitamin D supplementation are warranted.

[Impact of bariatric surgery on vitamin metabolisms in obese patients]

AIM

To investigate the impact of bariatric surgery (BS) on the level of vitamins in obese patients.

SUBJECTS AND METHODS

One hundred obese patients (78 women and 22 men) aged 19 to 61 years were examined. Controlled gastric banding (CGB) was carried out in 20 patients (mean body mass index (BMI), 41.3 ± 8.2 kg/m2); gastric sleeve resection (GSR) in 40 patients, and gastric shunting (GS) in 40 (the mean BMI in these groups were 41.1 ± 17.8 and 45.9 ± 6.2 kg/m2, respectively). A control group consisted of 10 apparently healthy individuals (BMI, 24.9 ± 3.2 kg/m2). An enzyme immunoassay was used to determine the serum concentrations of vitamins B1, B2, B5, B6, B9, B12, C, and D, niacin, biotin, and retinol-binding protein (RBP) before and 1 year after surgery.

RESULTS

All the three groups showed a considerable decrease in the levels of vitamins C, B5, B6, and D, and RBP both prior to and following BS. More than 50% of the patients who had undergone GSR had also a lower baseline niacin level. A year after CGB, GSR, and GS, the number of patents with deficiency of these vitamins remained the same or increased. The majority of patients with the same level of vitamin B2, niacin, and folic acid (FA) were observed to have its decrease a year postsurgery. The concentration of the other test vitamins was also reduced a year after all operations; however, it remained within the normal range. GS had no substantial impact on the concentrations of FA, vitamins B2, B12, B1, and biotin. The lower serum vitamin levels were not accompanied by clinical symptoms in most patients following BS.

CONCLUSION

In 80% of the patients with obesity, the levels of vitamins C, B6, and D were decreased to a variable degree. After BS, there was a rise in the number of patients with low serum vitamin C, D, B6, B5, niacin, FA, and RBP concentrations, at the same time the number of patients with FA deficiency increased by more than twice. BS did not significantly affect the metabolism of vitamins B1 B2 B12, and biotin.

Nutrition and metabolic support recommendations for the bariatric patient

Managing the metabolic needs of the patient with obesity is a challenge unto itself without the added demands of accounting for an altered gastrointestinal tract. Nevertheless, with about 200,000 bariatric procedures being performed annually in the United States, clinicians must be prepared to manage the critically ill bariatric surgery patient. This article reviews the recent literature relating to nutrient needs and metabolic support for the bariatric patient. Bariatric patients are at risk for several micronutrient deficiencies, including vitamins D and B₁₂, calcium, and iron; some bariatric procedures affect macronutrient needs as well. Literature on nutrition support guidelines for the bariatric population is limited. However, with an understanding of the anatomical and physiological effects of bariatric surgery, recent guidelines for critically ill patients with obesity can be applied to the bariatric surgery population. The unique needs of the bariatric population, such as susceptibility to micronutrient deficiencies and specialized access routes, must be considered to provide safe and efficacious nutrition support. Further research is necessary to develop specific nutrition support recommendations for the bariatric population.

Vitamin D status following bariatric surgery: implications and recommendations

Individuals with extreme obesity who qualify for bariatric surgery are frequently vitamin D deficient before and after surgery. The anatomical changes that occur during some bariatric procedures may lead to decreased absorption of vitamin D, although vitamin D absorption and metabolism has not been quantified or compared across surgeries, and multiple other factors could influence vitamin D status in these individuals. Vitamin D treatment and dosing studies show that there is variability in how individuals respond to supplementation regimens regardless of the bariatric procedure. It is unknown if improving vitamin D status before and/or after bariatric surgery can affect health-related outcomes in this population beyond the traditional roles of vitamin D. Vitamin D has been purported to positively influence a variety of obesity-related comorbidities. Furthermore, in light of the potential role of vitamin D in immunity and inflammation, it seems important to consider the ramifications of vitamin D deficiency in the postbariatric individual in the critical care setting and particularly in the context of aging. Additional research is needed to develop evidence-based guidelines for optimal treatment of vitamin D deficiency in individuals before and after bariatric surgery and to determine the impact of vitamin D repletion on non-bone health-related outcomes in these individuals.

Biliopancreatic diversion requires multiple vitamin and micronutrient adjustments within 2 years of surgery

BACKGROUND

Malabsorptive bariatric procedures require multiple vitamin supplements, especially regarding fat-soluble vitamins. The exact amount required to maintain normal serum concentrations is still largely unknown. Based on the initial postoperative prescription, we assessed the number of adjustments and the amount of vitamins/micronutrients to normalize the biological markers 2 years after the biliopancreatic diversion with duodenal switch (BPD/DS).

METHODS

A total of 112 consecutive patients had a laparoscopic BPD/DS between February 2007 and November 2010 for a body mass index of 53.1±5.9 kg/m² at a private hospital. Complete blood checks with vitamin status were obtained at each of the 3-month interval visits during the 1(st) postoperative year as well as twice during the 2(nd) year.

RESULTS

Initially, all of the patients were prescribed daily 25,000 International units (IU) of vitamin A, 1000 mg of calcium, multivitamins, and 1900 IU of vitamin D3. Significant adjustments were necessary 3.6±1.1 times during this period. A total of 80% of the patients required added vitamin A, vitamin D, as well as calcium, zinc, and iron. After 2 years,≥20% of patients exhibited vitamin A and iron deficiency with low prealbumin or micropenic anemia. Seventy percent had vitamin D deficiency and 50% secondary hyperparathyroidism.

CONCLUSION

The initial prescription was insufficient to cover the requirements after BPD/DS. At least 3000 mg of calcium with 7000 IU of vitamin D, 50,000 IU of vitamin A, 40 mg of zinc, and 200 mg of iron must be prescribed to start with. The trend toward a decrease in 25 OH vitamin D and hyperparathyroidism remains difficult to control although it can result from increased bone turnover during the early postoperative period.

Vitamin D signalling in adipose tissue

Vitamin D deficiency and the rapid increase in the prevalence of obesity are both considered important public health issues. The classical role of vitamin D is in Ca homoeostasis and bone metabolism. Growing evidence suggests that the vitamin D system has a range of physiological functions, with vitamin D deficiency contributing to the pathogenesis of several major diseases, including obesity and the metabolic syndrome. Clinical studies have shown that obese individuals tend to have a low vitamin D status, which may link to the dysregulation of white adipose tissue. Recent studies suggest that adipose tissue may be a direct target of vitamin D. The expression of both the vitamin D receptor and 25-hydroxyvitamin D 1α-hydroxylase (CYP27B1) genes has been shown in murine and human adipocytes. There is evidence that vitamin D affects body fat mass by inhibiting adipogenic transcription factors and lipid accumulation during adipocyte differentiation. Some recent studies demonstrate that vitamin D metabolites also influence adipokine production and the inflammatory response in adipose tissue. Therefore, vitamin D deficiency may compromise the normal metabolic functioning of adipose tissue. Given the importance of the tissue in energy balance, lipid metabolism and inflammation in obesity, understanding the mechanisms of vitamin D action in adipocytes may have a significant impact on the maintenance of metabolic health. In the present review, we focus on the signalling role of vitamin D in adipocytes, particularly the potential mechanisms through which vitamin D may influence adipose tissue development and function.

Nutritional deficiencies after bariatric surgery

Lifestyle intervention programmes often produce insufficient weight loss and poor weight loss maintenance. As a result, an increasing number of patients with obesity and related comorbidities undergo bariatric surgery, which includes approaches such as the adjustable gastric band or the 'divided' Roux-en-Y gastric bypass (RYGB). This Review summarizes the current knowledge on nutrient deficiencies that can develop after bariatric surgery and highlights follow-up and treatment options for bariatric surgery patients who develop a micronutrient deficiency. The major macronutrient deficiency after bariatric surgery is protein malnutrition. Deficiencies in micronutrients, which include trace elements, essential minerals, and water-soluble and fat-soluble vitamins, are common before bariatric surgery and often persist postoperatively, despite universal recommendations on multivitamin and mineral supplements. Other disorders, including small intestinal bacterial overgrowth, can promote micronutrient deficiencies, especially in patients with diabetes mellitus. Recognition of the clinical presentations of micronutrient deficiencies is important, both to enable early intervention and to minimize long-term adverse effects. A major clinical concern is the relationship between vitamin D deficiency and the development of metabolic bone diseases, such as osteoporosis or osteomalacia; metabolic bone diseases may explain the increased risk of hip fracture in patients after RYGB. Further studies are required to determine the optimal levels of nutrient supplementation and whether postoperative laboratory monitoring effectively detects nutrient deficiencies. In the absence of such data, clinicians should inquire about and treat symptoms that suggest nutrient deficiencies.

The link between obesity and low circulating 25-hydroxyvitamin D concentrations: considerations and implications

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.