Different threshold levels of circulating total and free 25-hydroxyvitamin D for the diagnosis of vitamin D deficiency in obese adolescents

Association of Blood Calcidiol Levels and Metabolic Syndrome in Children and Adolescents With Vitamin D Deficiency

This retrospective cohort study aimed to determine whether severe calcidiol deficiency [25-hydroxyvitamin (OH)D <30 nmol/L] improvement has a beneficial effect on cardiometabolic parameters in children and adolescents (5-17 years) with or without metabolic syndrome (MetS). Logistic regression analysis was performed to test for multivariate associations between potential confounders and changes in vitamin D (VD) status from baseline to follow-up care when predicting binary categorical outcomes. Of 562 participants, 146 (26%) had MetS. Individuals with severe VD deficiency (VDD) were more likely to have MetS with elevated blood pressure than those with sufficient (≥75 nmol) VD levels (adjusted odds ratio [AOR], 4.46; 1.08-18.43; p < .05) at follow-up. In the logistic regression model, every unit increase in VD across time decreased the odds of MetS (AOR, 0.98; 95% confidence interval: [0.96, 0.99]; p < .05). Improvement in VD status demonstrated a beneficial metabolic effect in children and adolescents with severe VDD.

Free and bioavailable 25-hydroxyvitamin D thresholds for bone metabolism and their associations with metabolic syndrome in Chinese women of childbearing age

Objective

The free hormone hypothesis suggests that free and bioavailable 25-hydroxyvitamin D [25(OH)D] may better reflect vitamin D bioactivity. This study aimed to determine the free and bioavailable 25(OH)D characteristics, estimate their thresholds based on parathyroid hormone (PTH) and bone turnover markers (BTMs), assess their associations with the risk of metabolic syndrome (MetS), and evaluate their potential advantages.

Methods

A cross-sectional study was conducted using a nationally representative database (n = 1,505, female, 18-45 years). Serum total 25(OH)D, vitamin D-binding protein, albumin, PTH, and BTMs [osteocalcin, β-CrossLaps of type 1 collagen containing cross-linked C-telopeptide (β-CTX), and procollagen type 1 N-terminal propeptide (P1NP)] were measured. Free 25(OH)D and bioavailable 25(OH)D were calculated. The threshold associations of 25(OH)D with PTH and BTMs were analyzed. The relationship between 25(OH)D and MetS risk was examined. An intervention study was then performed in 39 women (18-47 years) to assess the associations of increasing 25(OH)D with PTH and BTMs after vitamin D supplementation.

Results

In the cross-sectional study, the three forms of 25(OH)D were found to have similar distribution characteristics. Free and bioavailable 25(OH)D correlated well with total 25(OH)D. Significant total 25(OH)D cutoffs were observed for PTH (14.19 ng/mL and 18.03 ng/mL), osteocalcin (15.14 ng/mL), β-CTX (14.79 ng/mL), and P1NP (15.08 ng/mL). Free and bioavailable 25(OH)D cutoffs were only found for P1NP (3.47 pg/mL and 1.66 ng/mL, respectively). A total 25(OH)D of <15.14 ng/mL was marginally associated with a higher risk of reduced high-density lipoprotein cholesterol (HDL-C) [odd ratios (OR) = 1.371 (0.991-1.899)]. The ORs of higher versus lower free and bioavailable 25(OH)D levels for reduced HDL-C were 0.770 (0.621-0.956) and 0.772 (0.622-0.958), respectively. The results of the intervention study indicated that PTH and BTMs responded more sensitively to total 25(OH)D than to free or bioavailable 25(OH)D.

Conclusion

Free and bioavailable 25(OH)D only had a threshold effect on P1NP. The active 25(OH)D thresholds could be used for risk assessment of reduced HDL-C. However, no superiority of free or bioavailable 25(OH)D was found based on the response of PTH and BTMs to changes in 25(OH)D in Chinese women of childbearing age following vitamin D supplementation.

Clinical trial registration

http://www.chictr.org.cn, ChiCTR2200058290.

Association between Vitamin D Levels, Puberty Timing, and Age at Menarche

Pubertal development represents the process of physical maturation where an adolescent reaches sexual maturity and attains reproductive function. The effects of vitamin D are mainly mediated by the vitamin D receptor (VDR), which is expressed in almost all body cells, including the ovary and human pituitary gland and animal hypothalamus. Thus, vitamin D has gained great interest as pathogenic factor of pubertal disorders and fertility. This narrative review aimed to provide a broad overview of the available literature regarding the association between vitamin D levels, puberty timing, and age at menarche. A review of the data on the involvement of micronutrient deficiency, as a modifiable cause of pubertal disorders, is important for the prediction and prevention of deficiencies as well as for fertility protection and should be considered a public health priority. Reported data support that vitamin D is a regulator of neuroendocrine and ovarian physiology and, more in detail, a deficiency of vitamin D is involved in altered pubertal timing. Considering the long-term consequences of early pubertal development and early menarche, the detection of modifiable causes is crucial in preventive strategies. Future studies in humans and with an increased scale are needed to elucidate the vitamin D role in sexual maturation and puberty development.

The mediating role of bariatric surgery in the metabolic relationship between parathyroid hormone and 25-hydroxyvitamin D

Vitamin D metabolism is altered in obese individuals. Our findings indicated that in patients with severe obesity, a relatively low 25(OH)D concentration was required to suppress PTH. The PTH inflection point increased following surgery-induced weight loss, highlighting 25(OH)D different regulation mechanisms in patients with obesity.

INTRODUCTION

An optimal and sufficient concentration of 25-hydroxyvitamin D (25(OH)D) has been suggested as the level required to maximally suppress intact parathyroid hormone (iPTH). We evaluated the role of surgery-induced weight loss in determining the threshold(s) of 25(OH)D required to suppress iPTH.

METHODS

This study was conducted in the framework of the Tehran Obesity Treatment Study (TOTS). We prospectively analyzed 687 patients with severe obesity who participated in the TOTS and underwent bariatric surgery from March 2013 to March 2019. The patients were followed for 1 year after surgery. Anthropometric parameters and serum levels of iPTH, 25OHD, phosphorous, and calcium were measured. Nonlinear and piecewise linear regression was used to evaluate the relationship between 25(OH)D and iPTH and to determine the 25(OH)D-suppression point at which iPTH was maximally suppressed.

RESULTS

Body mass index was 44.6 kg/m² at the baseline and decreased to 29.7 kg/m² 1 year after surgery (P < 0.05). Before the surgery, iPTH and 25(OH)D showed an exponential relationship; iPTH began to decrease rapidly at 25(OH)D concentration of 12 ng/mL, reaching maximal suppression at 30 ng/mL. However, the relationship between 25(OH)D and iPTH was non-exponential 1 year after surgery. The piecewise linear regression model revealed the 25(OH)D concentration of 21 ng/mL as the inflection point following surgery-induced weight loss.

CONCLUSION

In patients with severe obesity, PTH was suppressed at a relatively lower concentration of 25(OH)D; this threshold increased following surgery-induced weight loss. These findings suggest a role for bariatric surgery in regulating 25(OH)D metabolism in patients with obesity.

Association between Suboptimal 25-Hydroxyvitamin D Status and Overweight/Obesity in Infants: A Prospective Cohort Study in China

This study aimed to investigate whether 25-hydroxyvitamin D (25(OH)D) concentrations are correlated to overweight/obesity in infants and to explore a threshold of 25(OH)D. A total of 1205 six-month-old infants from two community hospitals in Shanghai were randomly recruited, and 925 of them were followed up at 12 months. Concentration of 25(OH)D, weight, and length were measured at two time points. Overweight/obesity was defined as a weight-for-length Z-score >97th percentile. The prevalence of overweight/obesity at 6 and 12 months was 6.88% and 5.26%, respectively. The occurrence of vitamin D (VitD) deficiency (<20 ng/mL) at 6 and 12 months was 6.56% and 2.05%, respectively. Concentration of 25(OH)D at the corresponding age was negatively associated with weight-for-length percentile (WLP) at both 6 (adjusted β: −0.14; 95% CI: −0.27, −0.02; p = 0.02) and 12 months (adjusted β: −0.22; 95% CI: −0.41, −0.02; p = 0.03), while the relationship between 25(OH)D at 6 months and WLP at 12 months was nonlinear, where 35 ng/mL was identified as an inflection point. Those with a concentration of 25(OH)D <35 ng/mL at 6 months had a higher risk of overweight/obesity (adjusted OR: 1.42; 95% CI: 1.06, 1.91; p = 0.02) compared to the group with a concentration of 25(OH)D ≥35 ng/mL. Moreover, a concentration of 25(OH)D <35 ng/mL at two time points significantly increased the risk of overweight/obesity at 12 months compared to the group with 25(OH)D concentration ≥35 ng/mL at two time points (adjusted OR: 2.91; 95% CI: 1.13, 7.46; p = 0.03). A suboptimal 25(OH)D concentration <35 ng/mL significantly increases the risk of overweight/obesity in infants.

Vitamin D in pediatric patients with obesity and arterial hypertension

The purpose of this study was to find potential differences in vitamin D levels between different groups: overweight children with hypertension, normal-weight children with hypertension, overweight children with normal blood pressure and normal-weight children without hypertension, representing the control group. We also wanted to determine whether there are correlations between vitamin D levels and other clinical laboratory parameters, to evaluate the potential need for substitution. We measured vitamin D, homocysteine, total cholesterol, HDL, LDL, triglycerides, uric acid, glucose, apolipoprotein A1, apolipoprotein B, alkaline phosphatase, calcium, phosphate and magnesium serum levels in all groups. We also took anthropometric measurements (body weight, height, body mass index (BMI)) and observed patients' blood pressure. The results were analyzed with SPSS statistic tool with basic statistical methods. The study included 175 children between 5 and 18 years of age. Fiftyseven were healthy (group A-control group), 41 normal-weight with hypertension (group B), 44 overweight with hypertension (group C) and 33 overweight with normal blood pressure (group D). The results showed statistically significant differences in values of vitamin D between all groups-A and B (p = 0.003), A and C (p < 0.001), A and D (p < 0.001), B and D (p = 0.043), B and C (0.030), except for groups C and D (p = 0.830). There were statistically significant correlations between vitamin D and BMI (r = - 0.196, p = 0.010), systolic pressure (r = - 0.190, p = 0.002), diastolic pressure (r = - 0.149, p = 0.050), homocysteine (r = - 0.208, p = 0.007), triglycerides (r = - 0.196, p = 0.011) and apolipoprotein A1 (r = 0.222, p = 0.007), confirmed in multivariate model. For the blood pressure, the higher the systolic blood pressure, the lower the average vitamin D was. The pilot study shows significant differences in serum vitamin D levels between all groups of children, apart from groups C and D. These results, combined with statistically significant correlations between vitamin D and systolic and diastolic blood pressure suggest the need for monitoring and potential substitution of vitamin D in in pediatric patients with hypertension.