1.
Vitamin D and Calcium for the Prevention of Fracture: A Systematic Review and Meta-analysis.
Yao, P, Bennett, D, Mafham, M, Lin, X, Chen, Z, Armitage, J, Clarke, R
JAMA network open. 2019;(12):e1917789
Abstract
IMPORTANCE Vitamin D and calcium supplements are recommended for the prevention of fracture, but previous randomized clinical trials (RCTs) have reported conflicting results, with uncertainty about optimal doses and regimens for supplementation and their overall effectiveness. OBJECTIVE To assess the risks of fracture associated with differences in concentrations of 25-hydroxyvitamin D (25[OH]D) in observational studies and the risks of fracture associated with supplementation with vitamin D alone or in combination with calcium in RCTs. DATA SOURCES PubMed, EMBASE, Cochrane Library, and other RCT databases were searched from database inception until December 31, 2018. Searches were performed between July 2018 and December 2018. STUDY SELECTION Observational studies involving at least 200 fracture cases and RCTs enrolling at least 500 participants and reporting at least 10 incident fractures were included. Randomized clinical trials compared vitamin D or vitamin D and calcium with control. DATA EXTRACTION AND SYNTHESIS Two researchers independently extracted data according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines and assessed possible bias. Rate ratios (RRs) were estimated using fixed-effects meta-analysis. Data extraction and synthesis took place between July 2018 and June 2019. MAIN OUTCOMES AND MEASURES Any fracture and hip fracture. RESULTS In a meta-analysis of 11 observational studies (39 141 participants, 6278 fractures, 2367 hip fractures), each increase of 10.0 ng/mL (ie, 25 nmol/L) in 25 (OH)D concentration was associated with an adjusted RR for any fracture of 0.93 (95% CI, 0.89-0.96) and an adjusted RR for hip fracture of 0.80 (95% CI, 0.75-0.86). A meta-analysis of 11 RCTs (34 243 participants, 2843 fractures, 740 hip fractures) of vitamin D supplementation alone (daily or intermittent dose of 400-30 000 IU, yielding a median difference in 25[OH]D concentration of 8.4 ng/mL) did not find a reduced risk of any fracture (RR, 1.06; 95% CI, 0.98-1.14) or hip fracture (RR, 1.14; 95% CI, 0.98-1.32), but these trials were constrained by infrequent intermittent dosing, low daily doses of vitamin D, or an inadequate number of participants. In contrast, a meta-analysis of 6 RCTs (49 282 participants, 5449 fractures, 730 hip fractures) of combined supplementation with vitamin D (daily doses of 400-800 IU, yielding a median difference in 25[OH]D concentration of 9.2 ng/mL) and calcium (daily doses of 1000-1200 mg) found a 6% reduced risk of any fracture (RR, 0.94; 95% CI, 0.89-0.99) and a 16% reduced risk of hip fracture (RR, 0.84; 95% CI, 0.72-0.97). CONCLUSIONS AND RELEVANCE In this systematic review and meta-analysis, neither intermittent nor daily dosing with standard doses of vitamin D alone was associated with reduced risk of fracture, but daily supplementation with both vitamin D and calcium was a more promising strategy.
2.
Ascorbic Acid Supplements and Kidney Stones Incidence Among Men and Women: A systematic review and meta-analysis.
Jiang, K, Tang, K, Liu, H, Xu, H, Ye, Z, Chen, Z
Urology journal. 2019;(2):115-120
Abstract
PURPOSE The relationship of ascorbic acid (AA) supplements and risk of kidney stones among men and women is controversial. This systematic evaluation was performed to obtain comprehensive evidence about the relationship of AA supplements and risk of kidney stones among men and women. MATERIAL AND METHODS A systematic search of Pubmed, the Cochrane Library, Web of Science, Embase was performed to identify studies that exhibited the relationship of AA supplements and risk of kidney stones among men and women were published up to Mar 2017. Outcomes of interest included kidney stones incidence and risk factors. RESULTS Four studies estimating the association between AA supplements and risk of kidney stones were included for meta-analysis. The kidney stones incidence was significantly higher in men than women with AA supplements (OR= 1.62; 95% CI: 1.09 to 2.42; P=0.02). AA supplements (250-499mg/d, 1000-1499mg/d) was remarkably correlated with the risk of renal stones among men (OR= 1.14, 95% CI: 1.00 to 1.28, P=0.04; OR= 1.12, 95% CI: 1.11 to 1.13, P<0.00001; respectively). However, AA supplements (500-999 mg/d, >1500 mg/d) did not correlate with the risk of renal stones among men (OR= 1.20, 95% CI: 0.99 to 1.46, P=0.06; OR= 1.28, 95% CI: 1.00 to 1.63, P= 0.05; respectively). In addition, AA supplements (250-499mg/d, 500-999mg/d, 1000-1499mg/d, >1500mg/d) did not remarkably correlate with the risk of renal stones among women (OR= 1.00, 95% CI: 0.82 to 1.22, P=0.98; OR= 1.08, 95% CI: 0.99 to 1.18, P=0.09; OR= 0.99, 95% CI: 0.90 to 1.08, P=0.77; OR= 0.99, 95% CI: 0.99 to 1.09, P=0.88; respectively). CONCLUSIONS AA supplements was remarkably correlated with higher risk for kidney stones incidence in men, but not in women. Further multicenter, prospective and long-term follow-up RCTs are required to verify these findings.
3.
Exploration of the safe upper level of iodine intake in euthyroid Chinese adults: a randomized double-blind trial.
Sang, Z, Wang, PP, Yao, Z, Shen, J, Halfyard, B, Tan, L, Zhao, N, Wu, Y, Gao, S, Tan, J, et al
The American journal of clinical nutrition. 2012;(2):367-73
-
-
Free full text
-
Abstract
BACKGROUND The beneficial health effects associated with Universal Salt Iodization are well known. Yet, little is known about the possible adverse health effects in people with high iodine intake and the safe daily intake upper limit in the Chinese population. OBJECTIVE The objective of this study was to explore the safe upper level of total daily iodine intake among adults in China. DESIGN A 4-wk, double-blind, placebo-controlled, randomized controlled trial was conducted in 256 euthyroid adults. Participants were randomly assigned to 12 intervention groups with various iodine supplement doses ranging from 0 to 2000 μg/d. Total iodine intake included iodine from both supplements and diet. Multiple outcome measures were used to evaluate possible adverse effects, including thyroid function, thyroid size, and urinary iodine. RESULTS The mean iodine intake from the diets and salt intake of the participants were 105 ± 25 and 258 ± 101 μg/d, respectively. In comparison with the placebo group, all iodide-supplemented groups responded with significant increases in median urinary iodine concentrations (P < 0.05) and in thyroid-stimulating hormone concentration (P < 0.05). Thyroid volume decreased after 4 wk in the high-iodine intervention groups (1500-2000 μg). Subclinical hypothyroidism appeared in the groups that received 400 μg I (5%) and 500-2000 μg I (15-47%). CONCLUSIONS This study showed that subclinical hypothyroidism appeared in the participants who took the 400-μg I supplement, which provided a total iodine intake of ∼800 μg/d. Thus, we caution against a total daily iodine intake that exceeds 800 μg/d in China and recommend further research to determine a safe daily upper limit.